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<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/features/json_view/" rel="canonical"><link href=../types/template_parameters/ rel=prev><link href=../../integration/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>Zero-copy JSON views - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.ab4e12ef.min.css><link rel=stylesheet href=../../css/custom.css><link rel=stylesheet href=../../css/brand.css><link rel=stylesheet href=../../css/fig-sax.css><link rel=stylesheet href=../../css/fig-jsonview.css><link 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v3.7.0 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v3.6.1/ class=md-nav__link> <span class=md-ellipsis> v3.6.1 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v3.6.0/ class=md-nav__link> <span class=md-ellipsis> v3.6.0 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v3.5.0/ class=md-nav__link> <span class=md-ellipsis> v3.5.0 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v3.4.0/ class=md-nav__link> <span class=md-ellipsis> v3.4.0 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v3.3.0/ class=md-nav__link> <span class=md-ellipsis> v3.3.0 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v3.2.0/ class=md-nav__link> <span class=md-ellipsis> v3.2.0 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v3.1.2/ class=md-nav__link> <span class=md-ellipsis> v3.1.2 </span> </a> </li> <li class=md-nav__item> <a 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v2.0.9 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v2.0.8/ class=md-nav__link> <span class=md-ellipsis> v2.0.8 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v2.0.7/ class=md-nav__link> <span class=md-ellipsis> v2.0.7 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v2.0.6/ class=md-nav__link> <span class=md-ellipsis> v2.0.6 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v2.0.5/ class=md-nav__link> <span class=md-ellipsis> v2.0.5 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v2.0.4/ class=md-nav__link> <span class=md-ellipsis> v2.0.4 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v2.0.3/ class=md-nav__link> <span class=md-ellipsis> v2.0.3 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v2.0.2/ class=md-nav__link> <span class=md-ellipsis> v2.0.2 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v2.0.1/ class=md-nav__link> <span class=md-ellipsis> v2.0.1 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v2.0.0/ class=md-nav__link> <span class=md-ellipsis> v2.0.0 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v1.1.0/ class=md-nav__link> <span class=md-ellipsis> v1.1.0 </span> </a> </li> <li class=md-nav__item> <a href=../../home/releases/v1.0.0/ class=md-nav__link> <span class=md-ellipsis> v1.0.0 </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../../home/design_goals/ class=md-nav__link> <span class=md-ellipsis> Design goals </span> </a> </li> <li class=md-nav__item> <a href=../../home/architecture/ class=md-nav__link> <span class=md-ellipsis> Architecture </span> </a> </li> <li class=md-nav__item> <a href=../../home/customers/ class=md-nav__link> <span class=md-ellipsis> Customers </span> </a> </li> <li class=md-nav__item> <a href=../../home/sponsors/ class=md-nav__link> <span class=md-ellipsis> Sponsors </span> </a> </li> <li class=md-nav__item> <a href=../../home/debugging/ class=md-nav__link> <span class=md-ellipsis> Debugging </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--active md-nav__item--section md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2 checked> <div class="md-nav__link md-nav__container"> <a href=../ class="md-nav__link "> <span class=md-ellipsis> Features </span> </a> <label class="md-nav__link " for=__nav_2 id=__nav_2_label tabindex> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_2_label aria-expanded=true> <label class=md-nav__title for=__nav_2> <span class="md-nav__icon md-icon"></span> Features </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../arbitrary_types/ class=md-nav__link> <span class=md-ellipsis> Arbitrary Type Conversions </span> </a> </li> <li class=md-nav__item> <a href=../type_recipes/ class=md-nav__link> <span class=md-ellipsis> Recipes for Common Types </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2_4> <div class="md-nav__link md-nav__container"> <a href=../binary_formats/ class="md-nav__link "> <span class=md-ellipsis> Binary Formats </span> </a> <label class="md-nav__link " for=__nav_2_4 id=__nav_2_4_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_2_4_label aria-expanded=false> <label class=md-nav__title for=__nav_2_4> <span class="md-nav__icon md-icon"></span> Binary Formats </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../binary_formats/bjdata/ class=md-nav__link> <span class=md-ellipsis> BJData </span> </a> </li> <li class=md-nav__item> <a href=../binary_formats/bon8/ class=md-nav__link> <span class=md-ellipsis> BON8 </span> </a> </li> <li class=md-nav__item> <a href=../binary_formats/bson/ class=md-nav__link> <span class=md-ellipsis> BSON </span> </a> </li> <li class=md-nav__item> <a href=../binary_formats/cbor/ class=md-nav__link> <span class=md-ellipsis> CBOR </span> </a> </li> <li class=md-nav__item> <a href=../binary_formats/messagepack/ class=md-nav__link> <span class=md-ellipsis> MessagePack </span> </a> </li> <li class=md-nav__item> <a href=../binary_formats/ubjson/ class=md-nav__link> <span class=md-ellipsis> UBJSON </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../binary_values/ class=md-nav__link> <span class=md-ellipsis> Binary Values </span> </a> </li> <li class=md-nav__item> <a href=../comments/ class=md-nav__link> <span class=md-ellipsis> Comments </span> </a> </li> <li class=md-nav__item> <a href=../conversions/ class=md-nav__link> <span class=md-ellipsis> Converting values </span> </a> </li> <li class=md-nav__item> <a href=../creating_values/ class=md-nav__link> <span class=md-ellipsis> Creating JSON values </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2_9> <div class="md-nav__link md-nav__container"> <a href=../element_access/ class="md-nav__link "> <span class=md-ellipsis> Element Access </span> </a> <label class="md-nav__link " for=__nav_2_9 id=__nav_2_9_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_2_9_label aria-expanded=false> <label class=md-nav__title for=__nav_2_9> <span class="md-nav__icon md-icon"></span> Element Access </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../element_access/unchecked_access/ class=md-nav__link> <span class=md-ellipsis> Unchecked access: operator[] </span> </a> </li> <li class=md-nav__item> <a href=../element_access/checked_access/ class=md-nav__link> <span class=md-ellipsis> Checked access: at </span> </a> </li> <li class=md-nav__item> <a href=../element_access/default_value/ class=md-nav__link> <span class=md-ellipsis> Access with default value: value </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../iterators/ class=md-nav__link> <span class=md-ellipsis> Iterators </span> </a> </li> <li class=md-nav__item> <a href=../merge_patch/ class=md-nav__link> <span class=md-ellipsis> JSON Merge Patch </span> </a> </li> <li class=md-nav__item> <a href=../json_patch/ class=md-nav__link> <span class=md-ellipsis> JSON Patch and Diff </span> </a> </li> <li class=md-nav__item> <a href=../json_pointer/ class=md-nav__link> <span class=md-ellipsis> JSON Pointer </span> </a> </li> <li class=md-nav__item> <a href=../modifying_values/ class=md-nav__link> <span class=md-ellipsis> Modifying values </span> </a> </li> <li class=md-nav__item> <a href=../modules/ class=md-nav__link> <span class=md-ellipsis> Modules </span> </a> </li> <li class=md-nav__item> <a href=../namespace/ class=md-nav__link> <span class=md-ellipsis> nlohmann Namespace </span> </a> </li> <li class=md-nav__item> <a href=../no_exceptions/ class=md-nav__link> <span class=md-ellipsis> Working Without Exceptions </span> </a> </li> <li class=md-nav__item> <a href=../object_order/ class=md-nav__link> <span class=md-ellipsis> Object Order </span> </a> </li> <li class=md-nav__item> <a href=../performance/ class=md-nav__link> <span class=md-ellipsis> Performance </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2_20> <div class="md-nav__link md-nav__container"> <a href=../parsing/ class="md-nav__link "> <span class=md-ellipsis> Parsing </span> </a> <label class="md-nav__link " for=__nav_2_20 id=__nav_2_20_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_2_20_label aria-expanded=false> <label class=md-nav__title for=__nav_2_20> <span class="md-nav__icon md-icon"></span> Parsing </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../parsing/json_lines/ class=md-nav__link> <span class=md-ellipsis> JSON Lines </span> </a> </li> <li class=md-nav__item> <a href=../parsing/large_and_partial_input/ class=md-nav__link> <span class=md-ellipsis> Large, Streamed, and Partial Input </span> </a> </li> <li class=md-nav__item> <a href=../parsing/parse_exceptions/ class=md-nav__link> <span class=md-ellipsis> Parsing and Exceptions </span> </a> </li> <li class=md-nav__item> <a href=../parsing/parser_callbacks/ class=md-nav__link> <span class=md-ellipsis> Parser Callbacks </span> </a> </li> <li class=md-nav__item> <a href=../parsing/sax_interface/ class=md-nav__link> <span class=md-ellipsis> SAX Interface </span> </a> </li> <li class=md-nav__item> <a href=../parsing/untrusted_input/ class=md-nav__link> <span class=md-ellipsis> Parsing Untrusted Input </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../assertions/ class=md-nav__link> <span class=md-ellipsis> Runtime Assertions </span> </a> </li> <li class=md-nav__item> <a href=../serialization/ class=md-nav__link> <span class=md-ellipsis> Serialization </span> </a> </li> <li class=md-nav__item> <a href=../enum_conversion/ class=md-nav__link> <span class=md-ellipsis> Specializing enum conversion </span> </a> </li> <li class=md-nav__item> <a href=../macros/ class=md-nav__link> <span class=md-ellipsis> Supported Macros </span> </a> </li> <li class=md-nav__item> <a href=../trailing_commas/ class=md-nav__link> <span class=md-ellipsis> Trailing Commas </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_2_26> <div class="md-nav__link md-nav__container"> <a href=../types/ class="md-nav__link "> <span class=md-ellipsis> Types </span> </a> <label class="md-nav__link " for=__nav_2_26 id=__nav_2_26_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_2_26_label aria-expanded=false> <label class=md-nav__title for=__nav_2_26> <span class="md-nav__icon md-icon"></span> Types </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../types/number_handling/ class=md-nav__link> <span class=md-ellipsis> Number Handling </span> </a> </li> <li class=md-nav__item> <a href=../types/template_parameters/ class=md-nav__link> <span class=md-ellipsis> Template Parameter Requirements </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--active"> <input class="md-nav__toggle md-toggle" type=checkbox id=__toc> <label class="md-nav__link md-nav__link--active" for=__toc> <span class=md-ellipsis> Zero-copy JSON views </span> <span class="md-nav__icon md-icon"></span> </label> <a href=./ class="md-nav__link md-nav__link--active"> <span class=md-ellipsis> Zero-copy JSON views </span> </a> <nav class="md-nav md-nav--secondary" aria-label="Table of contents"> <label class=md-nav__title for=__toc> <span class="md-nav__icon md-icon"></span> Table of contents </label> <ul class=md-nav__list data-md-component=toc data-md-scrollfix> <li class=md-nav__item> <a href=#the-problem class=md-nav__link> <span class=md-ellipsis> The problem </span> </a> </li> <li class=md-nav__item> <a href=#the-idea class=md-nav__link> <span class=md-ellipsis> The idea </span> </a> </li> <li class=md-nav__item> <a href=#how-to-use-it class=md-nav__link> <span class=md-ellipsis> How to use it </span> </a> </li> <li class=md-nav__item> <a href=#ownership-and-lifetime class=md-nav__link> <span class=md-ellipsis> Ownership and lifetime </span> </a> </li> <li class=md-nav__item> <a href=#what-is-the-same-as-parse class=md-nav__link> <span class=md-ellipsis> What is the same as parse() </span> </a> </li> <li class=md-nav__item> <a href=#what-is-different class=md-nav__link> <span class=md-ellipsis> What is different </span> </a> </li> <li class=md-nav__item> <a href=#duplicate-keys class=md-nav__link> <span class=md-ellipsis> Duplicate keys </span> </a> </li> <li class=md-nav__item> <a href=#getting-values-out-without-copying class=md-nav__link> <span class=md-ellipsis> Getting values out without copying </span> </a> </li> <li class=md-nav__item> <a href=#writing-generic-code class=md-nav__link> <span class=md-ellipsis> Writing generic code </span> </a> <nav class=md-nav aria-label="Writing generic code"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#a-from_json-that-reads-views class=md-nav__link> <span class=md-ellipsis> A from_json() that reads views </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#writing-a-view-back class=md-nav__link> <span class=md-ellipsis> Writing a view back </span> </a> </li> <li class=md-nav__item> <a href=#editing-a-document class=md-nav__link> <span class=md-ellipsis> Editing a document </span> </a> <nav class=md-nav aria-label="Editing a document"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#why-editing-without-reformatting class=md-nav__link> <span class=md-ellipsis> Why: editing without reformatting </span> </a> </li> <li class=md-nav__item> <a href=#what-stays-valid-and-what-an-edit-costs class=md-nav__link> <span class=md-ellipsis> What stays valid, and what an edit costs </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#images class=md-nav__link> <span class=md-ellipsis> Images </span> </a> </li> <li class=md-nav__item> <a href=#choosing-between-json-ordered_json-the-sax-interface-and-json_view class=md-nav__link> <span class=md-ellipsis> Choosing between json, ordered_json, the SAX interface, and json_view </span> </a> </li> <li class=md-nav__item> <a href=#see-also class=md-nav__link> <span class=md-ellipsis> See also </span> </a> </li> <li class=md-nav__item> <a href=#version-history class=md-nav__link> <span class=md-ellipsis> Version history </span> </a> </li> </ul> </nav> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_3> <div class="md-nav__link md-nav__container"> <a href=../../integration/ class="md-nav__link "> <span class=md-ellipsis> Integration </span> </a> <label class="md-nav__link " for=__nav_3 id=__nav_3_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_3_label aria-expanded=false> <label class=md-nav__title for=__nav_3> <span class="md-nav__icon md-icon"></span> Integration </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../integration/migration_guide/ class=md-nav__link> <span class=md-ellipsis> Migration Guide </span> </a> </li> <li class=md-nav__item> <a href=../../integration/cmake/ class=md-nav__link> <span class=md-ellipsis> CMake </span> </a> </li> <li class=md-nav__item> <a href=../../integration/package_managers/ class=md-nav__link> <span class=md-ellipsis> Package Managers </span> </a> </li> <li class=md-nav__item> <a href=../../integration/pkg-config/ class=md-nav__link> <span class=md-ellipsis> Pkg-config </span> </a> </li> <li class=md-nav__item> <a href=../../integration/compile_times/ class=md-nav__link> <span class=md-ellipsis> Compile times </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4> <label class=md-nav__link for=__nav_4 id=__nav_4_label tabindex=0> <span class=md-ellipsis> API Documentation </span> <span class="md-nav__icon md-icon"></span> </label> <nav class=md-nav data-md-level=1 aria-labelledby=__nav_4_label aria-expanded=false> <label class=md-nav__title for=__nav_4> <span class="md-nav__icon md-icon"></span> API Documentation </label> <ul class=md-nav__list data-md-scrollfix> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4_1> <div class="md-nav__link md-nav__container"> <a href=../../api/basic_json/ class="md-nav__link "> <span class=md-ellipsis> basic_json </span> </a> <label class="md-nav__link " for=__nav_4_1 id=__nav_4_1_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_4_1_label aria-expanded=false> <label class=md-nav__title for=__nav_4_1> <span class="md-nav__icon md-icon"></span> basic_json </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../api/basic_json/basic_json/ class=md-nav__link> <span class=md-ellipsis> (Constructor) </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/~basic_json/ class=md-nav__link> <span class=md-ellipsis> (Destructor) </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/accept/ class=md-nav__link> <span class=md-ellipsis> accept </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/array/ class=md-nav__link> <span class=md-ellipsis> array </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/array_t/ class=md-nav__link> <span class=md-ellipsis> array_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/as_base_class/ class=md-nav__link> <span class=md-ellipsis> as_base_class </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/at/ class=md-nav__link> <span class=md-ellipsis> at </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/back/ class=md-nav__link> <span class=md-ellipsis> back </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/begin/ class=md-nav__link> <span class=md-ellipsis> begin </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/binary/ class=md-nav__link> <span class=md-ellipsis> binary </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/binary_t/ class=md-nav__link> <span class=md-ellipsis> binary_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/bjdata_version_t/ class=md-nav__link> <span class=md-ellipsis> bjdata_version_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/boolean_t/ class=md-nav__link> <span class=md-ellipsis> boolean_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/cbegin/ class=md-nav__link> <span class=md-ellipsis> cbegin </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/cbor_tag_handler_t/ class=md-nav__link> <span class=md-ellipsis> cbor_tag_handler_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/cend/ class=md-nav__link> <span class=md-ellipsis> cend </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/clear/ class=md-nav__link> <span class=md-ellipsis> clear </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/contains/ class=md-nav__link> <span class=md-ellipsis> contains </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/count/ class=md-nav__link> <span class=md-ellipsis> count </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/crbegin/ class=md-nav__link> <span class=md-ellipsis> crbegin </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/crend/ class=md-nav__link> <span class=md-ellipsis> crend </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/default_object_comparator_t/ class=md-nav__link> <span class=md-ellipsis> default_object_comparator_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/diff/ class=md-nav__link> <span class=md-ellipsis> diff </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/dump/ class=md-nav__link> <span class=md-ellipsis> dump </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/emplace/ class=md-nav__link> <span class=md-ellipsis> emplace </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/emplace_back/ class=md-nav__link> <span class=md-ellipsis> emplace_back </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/empty/ class=md-nav__link> <span class=md-ellipsis> empty </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/end/ class=md-nav__link> <span class=md-ellipsis> end </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/end_pos/ class=md-nav__link> <span class=md-ellipsis> end_pos </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/erase/ class=md-nav__link> <span class=md-ellipsis> erase </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/error_handler_t/ class=md-nav__link> <span class=md-ellipsis> error_handler_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/exception/ class=md-nav__link> <span class=md-ellipsis> exception </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/find/ class=md-nav__link> <span class=md-ellipsis> find </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/flatten/ class=md-nav__link> <span class=md-ellipsis> flatten </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/format_as/ class=md-nav__link> <span class=md-ellipsis> format_as </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/from_bjdata/ class=md-nav__link> <span class=md-ellipsis> from_bjdata </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/from_bon8/ class=md-nav__link> <span class=md-ellipsis> from_bon8 </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/from_bson/ class=md-nav__link> <span class=md-ellipsis> from_bson </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/from_cbor/ class=md-nav__link> <span class=md-ellipsis> from_cbor </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/from_msgpack/ class=md-nav__link> <span class=md-ellipsis> from_msgpack </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/from_ubjson/ class=md-nav__link> <span class=md-ellipsis> from_ubjson </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/front/ class=md-nav__link> <span class=md-ellipsis> front </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/get/ class=md-nav__link> <span class=md-ellipsis> get </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/get_allocator/ class=md-nav__link> <span class=md-ellipsis> get_allocator </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/get_binary/ class=md-nav__link> <span class=md-ellipsis> get_binary </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/get_ptr/ class=md-nav__link> <span class=md-ellipsis> get_ptr </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/get_ref/ class=md-nav__link> <span class=md-ellipsis> get_ref </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/get_to/ class=md-nav__link> <span class=md-ellipsis> get_to </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/std_formatter/ class=md-nav__link> <span class=md-ellipsis> std::formatter&lt;basic_json&gt; </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/std_hash/ class=md-nav__link> <span class=md-ellipsis> std::hash&lt;basic_json&gt; </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/input_format_t/ class=md-nav__link> <span class=md-ellipsis> input_format_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/insert/ class=md-nav__link> <span class=md-ellipsis> insert </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/invalid_iterator/ class=md-nav__link> <span class=md-ellipsis> invalid_iterator </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_array/ class=md-nav__link> <span class=md-ellipsis> is_array </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_binary/ class=md-nav__link> <span class=md-ellipsis> is_binary </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_boolean/ class=md-nav__link> <span class=md-ellipsis> is_boolean </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_discarded/ class=md-nav__link> <span class=md-ellipsis> is_discarded </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_null/ class=md-nav__link> <span class=md-ellipsis> is_null </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_number/ class=md-nav__link> <span class=md-ellipsis> is_number </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_number_float/ class=md-nav__link> <span class=md-ellipsis> is_number_float </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_number_integer/ class=md-nav__link> <span class=md-ellipsis> is_number_integer </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_number_unsigned/ class=md-nav__link> <span class=md-ellipsis> is_number_unsigned </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_object/ class=md-nav__link> <span class=md-ellipsis> is_object </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_primitive/ class=md-nav__link> <span class=md-ellipsis> is_primitive </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_string/ class=md-nav__link> <span class=md-ellipsis> is_string </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/is_structured/ class=md-nav__link> <span class=md-ellipsis> is_structured </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/items/ class=md-nav__link> <span class=md-ellipsis> items </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/json_base_class_t/ class=md-nav__link> <span class=md-ellipsis> json_base_class_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/json_serializer/ class=md-nav__link> <span class=md-ellipsis> json_serializer </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/max_size/ class=md-nav__link> <span class=md-ellipsis> max_size </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/meta/ class=md-nav__link> <span class=md-ellipsis> meta </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/merge_diff/ class=md-nav__link> <span class=md-ellipsis> merge_diff </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/merge_patch/ class=md-nav__link> <span class=md-ellipsis> merge_patch </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/number_float_t/ class=md-nav__link> <span class=md-ellipsis> number_float_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/number_integer_t/ class=md-nav__link> <span class=md-ellipsis> number_integer_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/number_unsigned_t/ class=md-nav__link> <span class=md-ellipsis> number_unsigned_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/object/ class=md-nav__link> <span class=md-ellipsis> object </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/object_comparator_t/ class=md-nav__link> <span class=md-ellipsis> object_comparator_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/object_t/ class=md-nav__link> <span class=md-ellipsis> object_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator_ValueType/ class=md-nav__link> <span class=md-ellipsis> operator ValueType </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator_value_t/ class=md-nav__link> <span class=md-ellipsis> operator value_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator%5B%5D/ class=md-nav__link> <span class=md-ellipsis> operator[] </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator%3D/ class=md-nav__link> <span class=md-ellipsis> operator= </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator%2B%3D/ class=md-nav__link> <span class=md-ellipsis> operator+= </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator_eq/ class=md-nav__link> <span class=md-ellipsis> operator== </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator_ne/ class=md-nav__link> <span class=md-ellipsis> operator!= </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator_lt/ class=md-nav__link> <span class=md-ellipsis> operator< </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator_gt/ class=md-nav__link> <span class=md-ellipsis> operator> </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator_le/ class=md-nav__link> <span class=md-ellipsis> operator<= </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator_ge/ class=md-nav__link> <span class=md-ellipsis> operator>= </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/operator_spaceship/ class=md-nav__link> <span class=md-ellipsis> operator<=> </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/out_of_range/ class=md-nav__link> <span class=md-ellipsis> out_of_range </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/other_error/ class=md-nav__link> <span class=md-ellipsis> other_error </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/parse/ class=md-nav__link> <span class=md-ellipsis> parse </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/parse_error/ class=md-nav__link> <span class=md-ellipsis> parse_error </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/parse_event_t/ class=md-nav__link> <span class=md-ellipsis> parse_event_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/parser_callback_t/ class=md-nav__link> <span class=md-ellipsis> parser_callback_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/patch/ class=md-nav__link> <span class=md-ellipsis> patch </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/patch_inplace/ class=md-nav__link> <span class=md-ellipsis> patch_inplace </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/push_back/ class=md-nav__link> <span class=md-ellipsis> push_back </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/rbegin/ class=md-nav__link> <span class=md-ellipsis> rbegin </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/rend/ class=md-nav__link> <span class=md-ellipsis> rend </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/sax_parse/ class=md-nav__link> <span class=md-ellipsis> sax_parse </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/size/ class=md-nav__link> <span class=md-ellipsis> size </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/start_pos/ class=md-nav__link> <span class=md-ellipsis> start_pos </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/string_t/ class=md-nav__link> <span class=md-ellipsis> string_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/swap/ class=md-nav__link> <span class=md-ellipsis> swap </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/std_swap/ class=md-nav__link> <span class=md-ellipsis> std::swap&lt;basic_json&gt; </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/to_bjdata/ class=md-nav__link> <span class=md-ellipsis> to_bjdata </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/to_bon8/ class=md-nav__link> <span class=md-ellipsis> to_bon8 </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/to_bson/ class=md-nav__link> <span class=md-ellipsis> to_bson </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/to_cbor/ class=md-nav__link> <span class=md-ellipsis> to_cbor </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/to_msgpack/ class=md-nav__link> <span class=md-ellipsis> to_msgpack </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/to_string/ class=md-nav__link> <span class=md-ellipsis> to_string </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/to_ubjson/ class=md-nav__link> <span class=md-ellipsis> to_ubjson </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/type/ class=md-nav__link> <span class=md-ellipsis> type </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/type_error/ class=md-nav__link> <span class=md-ellipsis> type_error </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/type_name/ class=md-nav__link> <span class=md-ellipsis> type_name </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/unflatten/ class=md-nav__link> <span class=md-ellipsis> unflatten </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/update/ class=md-nav__link> <span class=md-ellipsis> update </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/value/ class=md-nav__link> <span class=md-ellipsis> value </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/value_t/ class=md-nav__link> <span class=md-ellipsis> value_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json/with_t/ class=md-nav__link> <span class=md-ellipsis> with_t </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4_2> <div class="md-nav__link md-nav__container"> <a href=../../api/basic_json_document/ class="md-nav__link "> <span class=md-ellipsis> basic_json_document </span> </a> <label class="md-nav__link " for=__nav_4_2 id=__nav_4_2_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_4_2_label aria-expanded=false> <label class=md-nav__title for=__nav_4_2> <span class="md-nav__icon md-icon"></span> basic_json_document </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../api/basic_json_document/basic_json_document/ class=md-nav__link> <span class=md-ellipsis> (Constructor) </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/accept/ class=md-nav__link> <span class=md-ellipsis> accept </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/erase/ class=md-nav__link> <span class=md-ellipsis> erase </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/insert/ class=md-nav__link> <span class=md-ellipsis> insert </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/is_discarded/ class=md-nav__link> <span class=md-ellipsis> is_discarded </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/load/ class=md-nav__link> <span class=md-ellipsis> load </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/memory_usage/ class=md-nav__link> <span class=md-ellipsis> memory_usage </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/node_count/ class=md-nav__link> <span class=md-ellipsis> node_count </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/owns_source/ class=md-nav__link> <span class=md-ellipsis> owns_source </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/parse/ class=md-nav__link> <span class=md-ellipsis> parse </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/parse_copy/ class=md-nav__link> <span class=md-ellipsis> parse_copy </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/push_back/ class=md-nav__link> <span class=md-ellipsis> push_back </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/read/ class=md-nav__link> <span class=md-ellipsis> read </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/root/ class=md-nav__link> <span class=md-ellipsis> root </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/save/ class=md-nav__link> <span class=md-ellipsis> save </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/set/ class=md-nav__link> <span class=md-ellipsis> set </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/shrink_to_fit/ class=md-nav__link> <span class=md-ellipsis> shrink_to_fit </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_document/source/ class=md-nav__link> <span class=md-ellipsis> source </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4_3> <div class="md-nav__link md-nav__container"> <a href=../../api/basic_json_view/ class="md-nav__link "> <span class=md-ellipsis> basic_json_view </span> </a> <label class="md-nav__link " for=__nav_4_3 id=__nav_4_3_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_4_3_label aria-expanded=false> <label class=md-nav__title for=__nav_4_3> <span class="md-nav__icon md-icon"></span> basic_json_view </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../api/basic_json_view/basic_json_view/ class=md-nav__link> <span class=md-ellipsis> (Constructor) </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/at/ class=md-nav__link> <span class=md-ellipsis> at </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/back/ class=md-nav__link> <span class=md-ellipsis> back </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/begin/ class=md-nav__link> <span class=md-ellipsis> begin </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/cbegin/ class=md-nav__link> <span class=md-ellipsis> cbegin </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/cend/ class=md-nav__link> <span class=md-ellipsis> cend </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/contains/ class=md-nav__link> <span class=md-ellipsis> contains </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/count/ class=md-nav__link> <span class=md-ellipsis> count </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/dump/ class=md-nav__link> <span class=md-ellipsis> dump </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/empty/ class=md-nav__link> <span class=md-ellipsis> empty </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/end/ class=md-nav__link> <span class=md-ellipsis> end </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/find/ class=md-nav__link> <span class=md-ellipsis> find </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/front/ class=md-nav__link> <span class=md-ellipsis> front </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/get/ class=md-nav__link> <span class=md-ellipsis> get </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/get_string/ class=md-nav__link> <span class=md-ellipsis> get_string </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/get_to/ class=md-nav__link> <span class=md-ellipsis> get_to </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_array/ class=md-nav__link> <span class=md-ellipsis> is_array </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_binary/ class=md-nav__link> <span class=md-ellipsis> is_binary </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_boolean/ class=md-nav__link> <span class=md-ellipsis> is_boolean </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_discarded/ class=md-nav__link> <span class=md-ellipsis> is_discarded </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_null/ class=md-nav__link> <span class=md-ellipsis> is_null </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_number/ class=md-nav__link> <span class=md-ellipsis> is_number </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_number_float/ class=md-nav__link> <span class=md-ellipsis> is_number_float </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_number_integer/ class=md-nav__link> <span class=md-ellipsis> is_number_integer </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_number_unsigned/ class=md-nav__link> <span class=md-ellipsis> is_number_unsigned </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_object/ class=md-nav__link> <span class=md-ellipsis> is_object </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_primitive/ class=md-nav__link> <span class=md-ellipsis> is_primitive </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_string/ class=md-nav__link> <span class=md-ellipsis> is_string </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/is_structured/ class=md-nav__link> <span class=md-ellipsis> is_structured </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/items/ class=md-nav__link> <span class=md-ellipsis> items </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/materialize/ class=md-nav__link> <span class=md-ellipsis> materialize </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/number_format/ class=md-nav__link> <span class=md-ellipsis> number_format </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/number_token/ class=md-nav__link> <span class=md-ellipsis> number_token </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/operator_ltlt/ class=md-nav__link> <span class=md-ellipsis> operator<< </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/operator%5B%5D/ class=md-nav__link> <span class=md-ellipsis> operator[] </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/operator_eq/ class=md-nav__link> <span class=md-ellipsis> operator== </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/operator_ne/ class=md-nav__link> <span class=md-ellipsis> operator!= </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/size/ class=md-nav__link> <span class=md-ellipsis> size </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/source_offset/ class=md-nav__link> <span class=md-ellipsis> source_offset </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/type/ class=md-nav__link> <span class=md-ellipsis> type </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/type_name/ class=md-nav__link> <span class=md-ellipsis> type_name </span> </a> </li> <li class=md-nav__item> <a href=../../api/basic_json_view/value/ class=md-nav__link> <span class=md-ellipsis> value </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4_4> <div class="md-nav__link md-nav__container"> <a href=../../api/byte_container_with_subtype/ class="md-nav__link "> <span class=md-ellipsis> byte_container_with_subtype </span> </a> <label class="md-nav__link " for=__nav_4_4 id=__nav_4_4_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_4_4_label aria-expanded=false> <label class=md-nav__title for=__nav_4_4> <span class="md-nav__icon md-icon"></span> byte_container_with_subtype </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../api/byte_container_with_subtype/byte_container_with_subtype/ class=md-nav__link> <span class=md-ellipsis> (constructor) </span> </a> </li> <li class=md-nav__item> <a href=../../api/byte_container_with_subtype/clear_subtype/ class=md-nav__link> <span class=md-ellipsis> clear_subtype </span> </a> </li> <li class=md-nav__item> <a href=../../api/byte_container_with_subtype/has_subtype/ class=md-nav__link> <span class=md-ellipsis> has_subtype </span> </a> </li> <li class=md-nav__item> <a href=../../api/byte_container_with_subtype/operator_eq/ class=md-nav__link> <span class=md-ellipsis> operator== </span> </a> </li> <li class=md-nav__item> <a href=../../api/byte_container_with_subtype/operator_ne/ class=md-nav__link> <span class=md-ellipsis> operator!= </span> </a> </li> <li class=md-nav__item> <a href=../../api/byte_container_with_subtype/set_subtype/ class=md-nav__link> <span class=md-ellipsis> set_subtype </span> </a> </li> <li class=md-nav__item> <a href=../../api/byte_container_with_subtype/subtype/ class=md-nav__link> <span class=md-ellipsis> subtype </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4_5> <div class="md-nav__link md-nav__container"> <a href=../../api/adl_serializer/ class="md-nav__link "> <span class=md-ellipsis> adl_serializer </span> </a> <label class="md-nav__link " for=__nav_4_5 id=__nav_4_5_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_4_5_label aria-expanded=false> <label class=md-nav__title for=__nav_4_5> <span class="md-nav__icon md-icon"></span> adl_serializer </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../api/adl_serializer/from_json/ class=md-nav__link> <span class=md-ellipsis> from_json </span> </a> </li> <li class=md-nav__item> <a href=../../api/adl_serializer/to_json/ class=md-nav__link> <span class=md-ellipsis> to_json </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../../api/is_json_view/ class=md-nav__link> <span class=md-ellipsis> is_json_view </span> </a> </li> <li class=md-nav__item> <a href=../../api/json/ class=md-nav__link> <span class=md-ellipsis> json </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_document/ class=md-nav__link> <span class=md-ellipsis> json_document </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_editable_document/ class=md-nav__link> <span class=md-ellipsis> json_editable_document </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_editable_view/ class=md-nav__link> <span class=md-ellipsis> json_editable_view </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4_11> <div class="md-nav__link md-nav__container"> <a href=../../api/json_pointer/ class="md-nav__link "> <span class=md-ellipsis> json_pointer </span> </a> <label class="md-nav__link " for=__nav_4_11 id=__nav_4_11_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_4_11_label aria-expanded=false> <label class=md-nav__title for=__nav_4_11> <span class="md-nav__icon md-icon"></span> json_pointer </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../api/json_pointer/json_pointer/ class=md-nav__link> <span class=md-ellipsis> (Constructor) </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/back/ class=md-nav__link> <span class=md-ellipsis> back </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/empty/ class=md-nav__link> <span class=md-ellipsis> empty </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/front/ class=md-nav__link> <span class=md-ellipsis> front </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/operator_string_t/ class=md-nav__link> <span class=md-ellipsis> operator string_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/operator_eq/ class=md-nav__link> <span class=md-ellipsis> operator== </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/operator_ne/ class=md-nav__link> <span class=md-ellipsis> operator!= </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/operator_spaceship/ class=md-nav__link> <span class=md-ellipsis> operator<=> </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/operator_slash/ class=md-nav__link> <span class=md-ellipsis> operator/ </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/operator_slasheq/ class=md-nav__link> <span class=md-ellipsis> operator/= </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/parent_pointer/ class=md-nav__link> <span class=md-ellipsis> parent_pointer </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/pop_back/ class=md-nav__link> <span class=md-ellipsis> pop_back </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/pop_front/ class=md-nav__link> <span class=md-ellipsis> pop_front </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/push_back/ class=md-nav__link> <span class=md-ellipsis> push_back </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/push_front/ class=md-nav__link> <span class=md-ellipsis> push_front </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/string_t/ class=md-nav__link> <span class=md-ellipsis> string_t </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_pointer/to_string/ class=md-nav__link> <span class=md-ellipsis> to_string </span> </a> </li> </ul> </nav> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4_12> <div class="md-nav__link md-nav__container"> <a href=../../api/json_sax/ class="md-nav__link "> <span class=md-ellipsis> json_sax </span> </a> <label class="md-nav__link " for=__nav_4_12 id=__nav_4_12_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_4_12_label aria-expanded=false> <label class=md-nav__title for=__nav_4_12> <span class="md-nav__icon md-icon"></span> json_sax </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../api/json_sax/binary/ class=md-nav__link> <span class=md-ellipsis> binary </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/boolean/ class=md-nav__link> <span class=md-ellipsis> boolean </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/end_array/ class=md-nav__link> <span class=md-ellipsis> end_array </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/end_object/ class=md-nav__link> <span class=md-ellipsis> end_object </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/key/ class=md-nav__link> <span class=md-ellipsis> key </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/null/ class=md-nav__link> <span class=md-ellipsis> null </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/number_float/ class=md-nav__link> <span class=md-ellipsis> number_float </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/number_integer/ class=md-nav__link> <span class=md-ellipsis> number_integer </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/number_unsigned/ class=md-nav__link> <span class=md-ellipsis> number_unsigned </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/parse_error/ class=md-nav__link> <span class=md-ellipsis> parse_error </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/start_array/ class=md-nav__link> <span class=md-ellipsis> start_array </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/start_object/ class=md-nav__link> <span class=md-ellipsis> start_object </span> </a> </li> <li class=md-nav__item> <a href=../../api/json_sax/string/ class=md-nav__link> <span class=md-ellipsis> string </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=../../api/json_view/ class=md-nav__link> <span class=md-ellipsis> json_view </span> </a> </li> <li class=md-nav__item> <a href=../../api/operator_ltlt/ class=md-nav__link> <span class=md-ellipsis> operator<<(basic_json), operator<<(json_pointer) </span> </a> </li> <li class=md-nav__item> <a href=../../api/operator_gtgt/ class=md-nav__link> <span class=md-ellipsis> operator>>(basic_json) </span> </a> </li> <li class=md-nav__item> <a href=../../api/operator_literal_json/ class=md-nav__link> <span class=md-ellipsis> operator""_json </span> </a> </li> <li class=md-nav__item> <a href=../../api/operator_literal_json_pointer/ class=md-nav__link> <span class=md-ellipsis> operator""_json_pointer </span> </a> </li> <li class=md-nav__item> <a href=../../api/ordered_json/ class=md-nav__link> <span class=md-ellipsis> ordered_json </span> </a> </li> <li class=md-nav__item> <a href=../../api/ordered_json_document/ class=md-nav__link> <span class=md-ellipsis> ordered_json_document </span> </a> </li> <li class=md-nav__item> <a href=../../api/ordered_json_editable_document/ class=md-nav__link> <span class=md-ellipsis> ordered_json_editable_document </span> </a> </li> <li class=md-nav__item> <a href=../../api/ordered_json_editable_view/ class=md-nav__link> <span class=md-ellipsis> ordered_json_editable_view </span> </a> </li> <li class=md-nav__item> <a href=../../api/ordered_json_view/ class=md-nav__link> <span class=md-ellipsis> ordered_json_view </span> </a> </li> <li class=md-nav__item> <a href=../../api/ordered_map/ class=md-nav__link> <span class=md-ellipsis> ordered_map </span> </a> </li> <li class=md-nav__item> <a href=../../api/view_mode/ class=md-nav__link> <span class=md-ellipsis> view_mode </span> </a> </li> <li class="md-nav__item md-nav__item--nested"> <input class="md-nav__toggle md-toggle " type=checkbox id=__nav_4_25> <div class="md-nav__link md-nav__container"> <a href=../../api/macros/ class="md-nav__link "> <span class=md-ellipsis> macros </span> </a> <label class="md-nav__link " for=__nav_4_25 id=__nav_4_25_label tabindex=0> <span class="md-nav__icon md-icon"></span> </label> </div> <nav class=md-nav data-md-level=2 aria-labelledby=__nav_4_25_label aria-expanded=false> <label class=md-nav__title for=__nav_4_25> <span class="md-nav__icon md-icon"></span> macros </label> <ul class=md-nav__list data-md-scrollfix> <li class=md-nav__item> <a href=../../api/macros/json_assert/ class=md-nav__link> <span class=md-ellipsis> JSON_ASSERT </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_brace_init_copy_semantics/ class=md-nav__link> <span class=md-ellipsis> JSON_BRACE_INIT_COPY_SEMANTICS </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_throw_user/ class=md-nav__link> <span class=md-ellipsis> JSON_CATCH_USER, JSON_THROW_USER, JSON_TRY_USER </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_diagnostics/ class=md-nav__link> <span class=md-ellipsis> JSON_DIAGNOSTICS </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_delete_deprecated_functions/ 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class=md-nav__item> <a href=../../api/macros/json_has_cpp_11/ class=md-nav__link> <span class=md-ellipsis> JSON_HAS_CPP_11, JSON_HAS_CPP_14, JSON_HAS_CPP_17, JSON_HAS_CPP_20, JSON_HAS_CPP_23, JSON_HAS_CPP_26 </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_has_filesystem/ class=md-nav__link> <span class=md-ellipsis> JSON_HAS_EXPERIMENTAL_FILESYSTEM, JSON_HAS_FILESYSTEM </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_has_range_view_conversion/ class=md-nav__link> <span class=md-ellipsis> JSON_HAS_RANGE_VIEW_CONVERSION </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_has_ranges/ class=md-nav__link> <span class=md-ellipsis> JSON_HAS_RANGES </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_has_static_rtti/ class=md-nav__link> <span class=md-ellipsis> JSON_HAS_STATIC_RTTI </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_has_std_format/ class=md-nav__link> <span class=md-ellipsis> JSON_HAS_STD_FORMAT </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_has_three_way_comparison/ class=md-nav__link> <span class=md-ellipsis> JSON_HAS_THREE_WAY_COMPARISON </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_no_automatic_udls/ class=md-nav__link> <span class=md-ellipsis> JSON_NO_AUTOMATIC_UDLS </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_noexception/ class=md-nav__link> <span class=md-ellipsis> JSON_NOEXCEPTION </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_no_io/ class=md-nav__link> <span class=md-ellipsis> JSON_NO_IO </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_no_simd/ class=md-nav__link> <span class=md-ellipsis> JSON_NO_SIMD </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_no_thread_local/ class=md-nav__link> <span class=md-ellipsis> JSON_NO_THREAD_LOCAL </span> </a> </li> <li class=md-nav__item> <a 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class=md-nav__item> <a href=../../api/macros/json_use_implicit_conversions/ class=md-nav__link> <span class=md-ellipsis> JSON_USE_IMPLICIT_CONVERSIONS </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_use_legacy_discarded_value_comparison/ class=md-nav__link> <span class=md-ellipsis> JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_use_objects_for_enum_keyed_maps/ class=md-nav__link> <span class=md-ellipsis> JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/json_use_simdutf/ class=md-nav__link> <span class=md-ellipsis> JSON_USE_SIMDUTF </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/nlohmann_define_derived_type/ class=md-nav__link> <span class=md-ellipsis> NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/nlohmann_define_type_intrusive/ class=md-nav__link> <span class=md-ellipsis> NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/nlohmann_define_type_non_intrusive/ class=md-nav__link> <span class=md-ellipsis> NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/nlohmann_define_type_with_names/ class=md-nav__link> <span class=md-ellipsis> NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/nlohmann_json_namespace/ class=md-nav__link> <span class=md-ellipsis> NLOHMANN_JSON_NAMESPACE </span> </a> </li> <li class=md-nav__item> <a href=../../api/macros/nlohmann_json_namespace_begin/ class=md-nav__link> <span class=md-ellipsis> NLOHMANN_JSON_NAMESPACE_BEGIN, NLOHMANN_JSON_NAMESPACE_END </span> </a> </li> <li 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data-md-component=toc data-md-scrollfix> <li class=md-nav__item> <a href=#the-problem class=md-nav__link> <span class=md-ellipsis> The problem </span> </a> </li> <li class=md-nav__item> <a href=#the-idea class=md-nav__link> <span class=md-ellipsis> The idea </span> </a> </li> <li class=md-nav__item> <a href=#how-to-use-it class=md-nav__link> <span class=md-ellipsis> How to use it </span> </a> </li> <li class=md-nav__item> <a href=#ownership-and-lifetime class=md-nav__link> <span class=md-ellipsis> Ownership and lifetime </span> </a> </li> <li class=md-nav__item> <a href=#what-is-the-same-as-parse class=md-nav__link> <span class=md-ellipsis> What is the same as parse() </span> </a> </li> <li class=md-nav__item> <a href=#what-is-different class=md-nav__link> <span class=md-ellipsis> What is different </span> </a> </li> <li class=md-nav__item> <a href=#duplicate-keys class=md-nav__link> <span class=md-ellipsis> Duplicate keys </span> </a> </li> <li class=md-nav__item> <a href=#getting-values-out-without-copying class=md-nav__link> <span class=md-ellipsis> Getting values out without copying </span> </a> </li> <li class=md-nav__item> <a href=#writing-generic-code class=md-nav__link> <span class=md-ellipsis> Writing generic code </span> </a> <nav class=md-nav aria-label="Writing generic code"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#a-from_json-that-reads-views class=md-nav__link> <span class=md-ellipsis> A from_json() that reads views </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#writing-a-view-back class=md-nav__link> <span class=md-ellipsis> Writing a view back </span> </a> </li> <li class=md-nav__item> <a href=#editing-a-document class=md-nav__link> <span class=md-ellipsis> Editing a document </span> </a> <nav class=md-nav aria-label="Editing a document"> <ul class=md-nav__list> <li class=md-nav__item> <a href=#why-editing-without-reformatting class=md-nav__link> <span class=md-ellipsis> Why: editing without reformatting </span> </a> </li> <li class=md-nav__item> <a href=#what-stays-valid-and-what-an-edit-costs class=md-nav__link> <span class=md-ellipsis> What stays valid, and what an edit costs </span> </a> </li> </ul> </nav> </li> <li class=md-nav__item> <a href=#images class=md-nav__link> <span class=md-ellipsis> Images </span> </a> </li> <li class=md-nav__item> <a href=#choosing-between-json-ordered_json-the-sax-interface-and-json_view class=md-nav__link> <span class=md-ellipsis> Choosing between json, ordered_json, the SAX interface, and json_view </span> </a> </li> <li class=md-nav__item> <a href=#see-also class=md-nav__link> <span class=md-ellipsis> See also </span> </a> </li> <li class=md-nav__item> <a href=#version-history class=md-nav__link> <span class=md-ellipsis> Version history </span> </a> </li> </ul> </nav> </div> </div> </div> <div class=md-content data-md-component=content> <article class="md-content__inner md-typeset"> <a 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<h1 id=zero-copy-json-views>Zero-copy <abbr title="JavaScript Object Notation">JSON</abbr> views<a class=headerlink href=#zero-copy-json-views title="Permanent link">&para;</a></h1> <p><code class=highlight><span class=o>&lt;</span><span class=n>nlohmann</span><span class=o>/</span><span class=n>json_view</span><span class=p>.</span><span class=n>hpp</span><span class=o>&gt;</span></code> adds a read-only, non-owning way to look at a parsed <abbr title="JavaScript Object Notation">JSON</abbr> text, as an alternative to building a <a href=../../api/basic_json/ ><code>basic_json</code></a> tree with <a href=../../api/basic_json/parse/ ><code>parse()</code></a>.</p> <h2 id=the-problem>The problem<a class=headerlink href=#the-problem title="Permanent link">&para;</a></h2> <p><a href=../../api/basic_json/parse/ ><code>basic_json::parse()</code></a> builds a tree of <code>basic_json</code> values: one allocation for every array and object, and every string copied into its own <code>std::string</code>. That is the right trade-off when the program goes on to read and write the value freely, but it does more work than necessary when only a small part of a large <abbr title="JavaScript Object Notation">JSON</abbr> text is actually needed, or when the same text is parsed over and over (many small messages, for instance) and most of the resulting tree is thrown away almost immediately.</p> <h2 id=the-idea>The idea<a class=headerlink href=#the-idea title="Permanent link">&para;</a></h2> <p><a href=../../api/basic_json_document/parse/ ><code>basic_json_document::parse()</code></a> parses the same <abbr title="JavaScript Object Notation">JSON</abbr> grammar, with the same options, but instead of a tree it builds a flat index of the values it found: one <a href=../../home/architecture/#node-index-of-json-views>16-byte entry</a> per value (and one per object key), in document order. Integers are converted while parsing and stored in their entry. Floating-point numbers and strings are referenced in place in the source text: a float is converted when it is read, and only strings that contain escape sequences are decoded, into one shared buffer owned by the document.</p> <p><a href=../../api/basic_json_view/ ><code>basic_json_view</code></a> is a small, trivially copyable handle (two pointers) into that index. It gives you the read-only, type-inspection part of the <code>basic_json</code> interface — <a href=../../api/basic_json_view/type/ ><code>type()</code></a> and the <code>is_*()</code> predicates, <a href=../../api/basic_json_view/size/ ><code>size()</code></a>/<a href=../../api/basic_json_view/empty/ ><code>empty()</code></a> — as well as element access (<a href=../../api/basic_json_view/operator%5B%5D/ ><code>operator[]</code></a>, <a href=../../api/basic_json_view/at/ ><code>at</code></a>, <a href=../../api/basic_json_view/front/ ><code>front</code></a>/<a href=../../api/basic_json_view/back/ ><code>back</code></a>), lookup (<a href=../../api/basic_json_view/find/ ><code>find</code></a>, <a href=../../api/basic_json_view/contains/ ><code>contains</code></a>, <a href=../../api/basic_json_view/count/ ><code>count</code></a>), and iteration (<a href=../../api/basic_json_view/begin/ ><code>begin</code></a>/<a href=../../api/basic_json_view/end/ ><code>end</code></a>, <a href=../../api/basic_json_view/items/ ><code>items</code></a>) — without ever allocating a <code>basic_json</code> value. When you do need an actual <code>basic_json</code> value for a subtree, <a href=../../api/basic_json_view/materialize/ ><code>materialize()</code></a> builds exactly the one <a href=../../api/basic_json/parse/ ><code>parse()</code></a> would have produced for it.</p> <p>The same small text, parsed both ways:</p> <div class=nj-fig-wrap> <p><svg class="nj-fig nj-jsonview " viewbox="0 0 840 692" role=img aria-labelledby="fig-jvl-title fig-jvl-title-d" xmlns=http://www.w3.org/2000/svg> <title id=fig-jvl-title>The same J&#8203;SON text parsed by basic_json::parse() and by json_document::parse()</title> <desc id=fig-jvl-title-d>The text {&quot;port&quot;: 6379, &quot;price&quot;: 19.90, &quot;tags&quot;: [&quot;eu&quot;, &quot;a\&quot;b&quot;]}. Top: basic_json::parse() builds a tree: the root json value points to a std::map whose three nodes are separate heap allocations; the price is stored as the double 19.9; the tags array is a std::vector of two json values, each pointing to its own std::string. Bottom: json_document::parse() keeps the 54 bytes of source text and builds a flat index of nine 16-byte nodes in document order: object, key port, unsigned integer 6379 (the converted value is in the node), key price, float, key tags, array, string eu, and an escaped string. Keys, the float, and the plain string point back into the source text; the escaped string points into the document&#x27;s buffer of decoded strings. A json_view is two pointers: one to the document and one to a node, here the array.</desc> <defs> <marker id=jvl-line viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-line nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jvl-str viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-str nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jvl-key viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-key nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jvl-num viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-num nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jvl-dec viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-dec nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jvl-own viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-own nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jvl-struct viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-struct nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jvl-bad viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-bad nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> </defs> <text class=nj-jsonview-h x=16 y=26 xml:space=preserve>basic_json::parse(): a tree, every array, object, and string in its own heap allocation</text> <rect class=nj-jsonview-box x=16 y=98 width=60 height=34 rx=5 /> <text class=nj-jsonview-mono x=46 y=120 text-anchor=middle xml:space=preserve>json</text> <path class="nj-jsonview-arr nj-jsonview-c-line" marker-end=url(#jvl-line) d="M76 115 L106 115"/> <rect class=nj-jsonview-heap x=108 y=98 width=84 height=34 rx=5 /> <text class=nj-jsonview-mono x=150 y=120 text-anchor=middle xml:space=preserve>std::map</text> <path class="nj-jsonview-arr nj-jsonview-c-line" marker-end=url(#jvl-line) d="M192 115 C192 115 226 67 226 67"/> <rect class=nj-jsonview-heap x=228 y=50 width=180 height=34 rx=5 /> <text class="nj-jsonview-mono nj-jsonview-c-key" x=240 y=72 xml:space=preserve>&quot;port&quot;</text> <text class="nj-jsonview-mono nj-jsonview-c-num" x=396 y=72 text-anchor=end xml:space=preserve>6379</text> <path class="nj-jsonview-arr nj-jsonview-c-line" marker-end=url(#jvl-line) d="M192 115 C192 115 226 115 226 115"/> <rect class=nj-jsonview-heap x=228 y=98 width=180 height=34 rx=5 /> <text class="nj-jsonview-mono nj-jsonview-c-key" x=240 y=120 xml:space=preserve>&quot;price&quot;</text> <text class="nj-jsonview-mono nj-jsonview-c-num" x=396 y=120 text-anchor=end xml:space=preserve>19.9</text> <text class=nj-jsonview-note x=418 y=120 xml:space=preserve>double: 19.90 is gone</text> <path class="nj-jsonview-arr nj-jsonview-c-line" marker-end=url(#jvl-line) d="M192 115 C192 115 226 163 226 163"/> <rect class=nj-jsonview-heap x=228 y=146 width=180 height=34 rx=5 /> <text class="nj-jsonview-mono nj-jsonview-c-key" x=240 y=168 xml:space=preserve>&quot;tags&quot;</text> <text class="nj-jsonview-mono nj-jsonview-c-line" x=396 y=168 text-anchor=end xml:space=preserve>•</text> <path class="nj-jsonview-arr nj-jsonview-c-line" marker-end=url(#jvl-line) d="M408 163 L442 163"/> <rect class=nj-jsonview-heap x=444 y=146 width=104 height=34 rx=5 /> <text class=nj-jsonview-mono x=496 y=168 text-anchor=middle xml:space=preserve>std::vector</text> <path class="nj-jsonview-arr nj-jsonview-c-line" marker-end=url(#jvl-line) d="M548 163 L576 163"/> <rect class=nj-jsonview-heap x=578 y=146 width=92 height=34 rx=5 /> <path class=nj-jsonview-sep d="M624 146 V180"/> <text class=nj-jsonview-mono x=601 y=168 text-anchor=middle xml:space=preserve>json</text> <text class=nj-jsonview-mono x=647 y=168 text-anchor=middle xml:space=preserve>json</text> <path class="nj-jsonview-arr nj-jsonview-c-line" marker-end=url(#jvl-line) d="M601 146 C601 126 706 150 706 130"/> <path class="nj-jsonview-arr nj-jsonview-c-line" marker-end=url(#jvl-line) d="M647 180 C647 200 706 176 706 196"/> <rect class=nj-jsonview-heap x=708 y=113 width=126 height=34 rx=5 /> <text class="nj-jsonview-mono nj-jsonview-sm nj-jsonview-c-str" x=771 y=135 text-anchor=middle xml:space=preserve>std::string eu</text> <rect class=nj-jsonview-heap x=708 y=179 width=126 height=34 rx=5 /> <text class="nj-jsonview-mono nj-jsonview-sm nj-jsonview-c-str" x=771 y=201 text-anchor=middle xml:space=preserve>std::string a&quot;b</text> <rect class=nj-jsonview-heap x=16 y=186 width=18 height=14 rx=3 /> <text class=nj-jsonview-note x=42 y=198 xml:space=preserve>a separate heap allocation</text> <path class=nj-jsonview-sep d="M16 234 H824"/> <text class=nj-jsonview-h x=16 y=262 xml:space=preserve>json_document::parse(): the source text stays where it is; one flat index of 16-byte nodes</text> <text class=nj-jsonview-note x=16 y=290 xml:space=preserve>source text, 54 bytes (borrowed, or owned by the document)</text> <rect class=nj-jsonview-ribbon x=42 y=300 width=756 height=26 rx=4 /> <rect x=71 y=302 width=54 height=22 rx=3 class="nj-jsonview-span nj-jsonview-c-key"/> <rect x=169 y=302 width=54 height=22 rx=3 class="nj-jsonview-span nj-jsonview-c-num"/> <rect x=267 y=302 width=68 height=22 rx=3 class="nj-jsonview-span nj-jsonview-c-key"/> <rect x=379 y=302 width=68 height=22 rx=3 class="nj-jsonview-span nj-jsonview-c-num"/> <rect x=491 y=302 width=54 height=22 rx=3 class="nj-jsonview-span nj-jsonview-c-key"/> <rect x=617 y=302 width=26 height=22 rx=3 class="nj-jsonview-span nj-jsonview-c-str"/> <rect x=701 y=302 width=54 height=22 rx=3 class="nj-jsonview-span nj-jsonview-c-dec"/> <text class="nj-jsonview-mono nj-jsonview-byte" x=49 y=317.5 text-anchor=middle xml:space=preserve>{</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=63 y=317.5 text-anchor=middle xml:space=preserve>&quot;</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=77 y=317.5 text-anchor=middle xml:space=preserve>p</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=91 y=317.5 text-anchor=middle xml:space=preserve>o</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=105 y=317.5 text-anchor=middle xml:space=preserve>r</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=119 y=317.5 text-anchor=middle xml:space=preserve>t</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=133 y=317.5 text-anchor=middle xml:space=preserve>&quot;</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=147 y=317.5 text-anchor=middle xml:space=preserve>:</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=175 y=317.5 text-anchor=middle xml:space=preserve>6</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=189 y=317.5 text-anchor=middle xml:space=preserve>3</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=203 y=317.5 text-anchor=middle xml:space=preserve>7</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=217 y=317.5 text-anchor=middle xml:space=preserve>9</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=231 y=317.5 text-anchor=middle xml:space=preserve>,</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=259 y=317.5 text-anchor=middle xml:space=preserve>&quot;</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=273 y=317.5 text-anchor=middle xml:space=preserve>p</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=287 y=317.5 text-anchor=middle xml:space=preserve>r</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=301 y=317.5 text-anchor=middle xml:space=preserve>i</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=315 y=317.5 text-anchor=middle xml:space=preserve>c</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=329 y=317.5 text-anchor=middle xml:space=preserve>e</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=343 y=317.5 text-anchor=middle xml:space=preserve>&quot;</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=357 y=317.5 text-anchor=middle xml:space=preserve>:</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=385 y=317.5 text-anchor=middle xml:space=preserve>1</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=399 y=317.5 text-anchor=middle xml:space=preserve>9</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=413 y=317.5 text-anchor=middle xml:space=preserve>.</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=427 y=317.5 text-anchor=middle xml:space=preserve>9</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=441 y=317.5 text-anchor=middle xml:space=preserve>0</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=455 y=317.5 text-anchor=middle xml:space=preserve>,</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=483 y=317.5 text-anchor=middle xml:space=preserve>&quot;</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=497 y=317.5 text-anchor=middle xml:space=preserve>t</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=511 y=317.5 text-anchor=middle xml:space=preserve>a</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=525 y=317.5 text-anchor=middle xml:space=preserve>g</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=539 y=317.5 text-anchor=middle xml:space=preserve>s</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=553 y=317.5 text-anchor=middle xml:space=preserve>&quot;</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=567 y=317.5 text-anchor=middle xml:space=preserve>:</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=595 y=317.5 text-anchor=middle xml:space=preserve>[</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=609 y=317.5 text-anchor=middle xml:space=preserve>&quot;</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=623 y=317.5 text-anchor=middle xml:space=preserve>e</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=637 y=317.5 text-anchor=middle xml:space=preserve>u</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=651 y=317.5 text-anchor=middle xml:space=preserve>&quot;</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=665 y=317.5 text-anchor=middle xml:space=preserve>,</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=693 y=317.5 text-anchor=middle xml:space=preserve>&quot;</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=707 y=317.5 text-anchor=middle xml:space=preserve>a</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=721 y=317.5 text-anchor=middle xml:space=preserve>\</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=735 y=317.5 text-anchor=middle xml:space=preserve>&quot;</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=749 y=317.5 text-anchor=middle xml:space=preserve>b</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=763 y=317.5 text-anchor=middle xml:space=preserve>&quot;</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=777 y=317.5 text-anchor=middle xml:space=preserve>]</text> <text class="nj-jsonview-mono nj-jsonview-byte" x=791 y=317.5 text-anchor=middle xml:space=preserve>}</text> <text class=nj-jsonview-tiny x=49 y=340 text-anchor=middle xml:space=preserve>0</text> <text class=nj-jsonview-tiny x=189 y=340 text-anchor=middle xml:space=preserve>10</text> <text class=nj-jsonview-tiny x=329 y=340 text-anchor=middle xml:space=preserve>20</text> <text class=nj-jsonview-tiny x=469 y=340 text-anchor=middle xml:space=preserve>30</text> <text class=nj-jsonview-tiny x=609 y=340 text-anchor=middle xml:space=preserve>40</text> <text class=nj-jsonview-tiny x=749 y=340 text-anchor=middle xml:space=preserve>50</text> <rect class=nj-jsonview-frame x=16 y=366 width=808 height=254 rx=10 /> <text class="nj-jsonview-note nj-jsonview-strong" x=30 y=602 xml:space=preserve>json_document: owns the node index and the buffer of decoded strings</text> <text class=nj-jsonview-note x=30 y=500 xml:space=preserve>node index: 9 nodes × 16 bytes = 144 bytes, in document order</text> <rect x=36 y=406 width=84 height=68 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=42 y=420 xml:space=preserve>0</text> <text class="nj-jsonview-kind nj-jsonview-c-struct" x=78 y=434 text-anchor=middle xml:space=preserve>object</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=78 y=451 text-anchor=middle xml:space=preserve>len 3</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=78 y=465 text-anchor=middle xml:space=preserve>next 9</text> <rect x=124 y=406 width=84 height=68 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=130 y=420 xml:space=preserve>1</text> <text class="nj-jsonview-kind nj-jsonview-c-key" x=166 y=434 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=166 y=451 text-anchor=middle xml:space=preserve>off 2</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=166 y=465 text-anchor=middle xml:space=preserve>len 4</text> <path class="nj-jsonview-arr nj-jsonview-c-key" marker-end=url(#jvl-key) d="M166 406 C166 367 98 367 98 328"/> <rect x=212 y=406 width=84 height=68 rx=5 class="nj-jsonview-node nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=218 y=420 xml:space=preserve>2</text> <text class="nj-jsonview-kind nj-jsonview-c-num" x=254 y=434 text-anchor=middle xml:space=preserve>uint</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=254 y=451 text-anchor=middle xml:space=preserve>6379</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=254 y=465 text-anchor=middle xml:space=preserve>(converted)</text> <rect x=300 y=406 width=84 height=68 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=306 y=420 xml:space=preserve>3</text> <text class="nj-jsonview-kind nj-jsonview-c-key" x=342 y=434 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=342 y=451 text-anchor=middle xml:space=preserve>off 16</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=342 y=465 text-anchor=middle xml:space=preserve>len 5</text> <path class="nj-jsonview-arr nj-jsonview-c-key" marker-end=url(#jvl-key) d="M342 406 C342 367 301 367 301 328"/> <rect x=388 y=406 width=84 height=68 rx=5 class="nj-jsonview-node nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=394 y=420 xml:space=preserve>4</text> <text class="nj-jsonview-kind nj-jsonview-c-num" x=430 y=434 text-anchor=middle xml:space=preserve>float</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=430 y=451 text-anchor=middle xml:space=preserve>off 24</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=430 y=465 text-anchor=middle xml:space=preserve>len 5</text> <path class="nj-jsonview-arr nj-jsonview-c-num" marker-end=url(#jvl-num) d="M430 406 C430 367 413 367 413 328"/> <rect x=476 y=406 width=84 height=68 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=482 y=420 xml:space=preserve>5</text> <text class="nj-jsonview-kind nj-jsonview-c-key" x=518 y=434 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=518 y=451 text-anchor=middle xml:space=preserve>off 32</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=518 y=465 text-anchor=middle xml:space=preserve>len 4</text> <path class="nj-jsonview-arr nj-jsonview-c-key" marker-end=url(#jvl-key) d="M518 406 C518 367 518 367 518 328"/> <rect x=564 y=406 width=84 height=68 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=570 y=420 xml:space=preserve>6</text> <text class="nj-jsonview-kind nj-jsonview-c-struct" x=606 y=434 text-anchor=middle xml:space=preserve>array</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=606 y=451 text-anchor=middle xml:space=preserve>len 2</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=606 y=465 text-anchor=middle xml:space=preserve>next 3</text> <rect x=652 y=406 width=84 height=68 rx=5 class="nj-jsonview-node nj-jsonview-c-str"/> <text class=nj-jsonview-tiny x=658 y=420 xml:space=preserve>7</text> <text class="nj-jsonview-kind nj-jsonview-c-str" x=694 y=434 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=694 y=451 text-anchor=middle xml:space=preserve>off 41</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=694 y=465 text-anchor=middle xml:space=preserve>len 2</text> <path class="nj-jsonview-arr nj-jsonview-c-str" marker-end=url(#jvl-str) d="M694 406 C694 367 630 367 630 328"/> <rect x=740 y=406 width=84 height=68 rx=5 class="nj-jsonview-node nj-jsonview-c-dec"/> <text class=nj-jsonview-tiny x=746 y=420 xml:space=preserve>8</text> <text class="nj-jsonview-kind nj-jsonview-c-dec" x=782 y=434 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=782 y=451 text-anchor=middle xml:space=preserve>escaped</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=782 y=465 text-anchor=middle xml:space=preserve>len 3</text> <text class=nj-jsonview-note x=773 y=568 text-anchor=middle xml:space=preserve>decoded strings</text> <rect x=740 y=518 width=66 height=30 rx=4 class="nj-jsonview-node nj-jsonview-c-dec"/> <text class=nj-jsonview-mono x=751 y=538 text-anchor=middle xml:space=preserve>a</text> <text class=nj-jsonview-mono x=773 y=538 text-anchor=middle xml:space=preserve>&quot;</text> <text class=nj-jsonview-mono x=795 y=538 text-anchor=middle xml:space=preserve>b</text> <path class="nj-jsonview-arr nj-jsonview-c-dec" marker-end=url(#jvl-dec) d="M782 474 C782 496 773 496 773 518"/> <text class="nj-jsonview-mono nj-jsonview-sm" x=470 y=670 text-anchor=end xml:space=preserve>json_view v = doc.root()[&quot;tags&quot;]</text> <rect x=480 y=648 width=140 height=34 rx=6 class="nj-jsonview-node nj-jsonview-c-struct"/> <path class=nj-jsonview-sep d="M550 648 V682"/> <text class=nj-jsonview-mono x=515 y=670 text-anchor=middle xml:space=preserve>doc*</text> <text class=nj-jsonview-mono x=585 y=670 text-anchor=middle xml:space=preserve>node*</text> <path class="nj-jsonview-arr nj-jsonview-c-struct" marker-end=url(#jvl-struct) d="M515 648 L515 622"/> <path class="nj-jsonview-arr nj-jsonview-c-struct" marker-end=url(#jvl-struct) d="M585 648 C585 561 606 561 606 474"/> <text class=nj-jsonview-note x=30 y=524 xml:space=preserve>integers are converted while parsing and kept in their node;</text> <text class=nj-jsonview-note x=30 y=542 xml:space=preserve>floats and strings point back into the text</text> </svg></p> </div> <p class=nj-caption>Top: the tree of separate heap allocations that <code>basic_json::parse()</code> builds. Bottom: <code>json_document::parse()</code> keeps the source text and builds one flat index of 16-byte nodes that point back into it, plus a buffer of decoded strings.</p> <h2 id=how-to-use-it>How to use it<a class=headerlink href=#how-to-use-it title="Permanent link">&para;</a></h2> <p>Include <code>&lt;nlohmann/json_view.hpp&gt;</code> in addition to (or instead of) <code>&lt;nlohmann/json.hpp&gt;</code>. Parse into a <a href=../../api/json_document/ ><code>json_document</code></a>, inspect its <a href=../../api/basic_json_document/root/ ><code>root()</code></a>, and <code>materialize()</code> when you need a real value. <code>materialize()</code> works on any view, not just the root, so you can turn just the subtree you need into a value:</p> <details class=example> <summary>Example: parse a document, inspect its root, and materialize it</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json_document</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=p>;</span>
<span class=w> </span><span class=c1>// json_document is basic_json_document&lt;nlohmann::json&gt;: same value types</span>
<span class=w> </span><span class=c1>// and containers as the ordinary json specialization</span>
<span class=w> </span><span class=n>json_document</span><span class=w> </span><span class=n>doc</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json_document</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"pi": 3.14, "numbers": [1, 2, 3]}</span><span class=dl>)</span><span class=s>"</span><span class=p>);</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>doc</span><span class=p>.</span><span class=n>root</span><span class=p>().</span><span class=n>is_object</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>doc</span><span class=p>.</span><span class=n>root</span><span class=p>().</span><span class=n>materialize</span><span class=p>().</span><span class=n>dump</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
<span class=p>{</span><span class=nt>"numbers"</span><span class=p>:[</span><span class=mi>1</span><span class=p>,</span><span class=mi>2</span><span class=p>,</span><span class=mi>3</span><span class=p>],</span><span class=nt>"pi"</span><span class=p>:</span><span class=mf>3.14</span><span class=p>}</span>
</code></pre></div> </details> <p><a href=../../api/ordered_json_document/ ><code>ordered_json_document</code></a> is the equivalent for <a href=../../api/ordered_json/ ><code>ordered_json</code></a>, just as <a href=../../api/ordered_json/ ><code>ordered_json</code></a> is to <a href=../../api/json/ ><code>json</code></a>.</p> <h2 id=ownership-and-lifetime>Ownership and lifetime<a class=headerlink href=#ownership-and-lifetime title="Permanent link">&para;</a></h2> <p>A document either <strong>borrows</strong> the text it was parsed from, or <strong>owns</strong> its own copy of it; call <a href=../../api/basic_json_document/owns_source/ ><code>owns_source()</code></a> to find out which happened. <a href=../../api/basic_json_document/parse/ ><code>parse()</code></a> decides this from the value category and type of its argument (an lvalue <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> is borrowed; an rvalue <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> is moved in, owned without a copy; a stream is read into an owned buffer; and so on — see <a href=../../api/basic_json_document/parse/#notes><code>parse</code>'s Notes</a> for the full table). <a href=../../api/basic_json_document/parse_copy/ ><code>parse_copy()</code></a> always owns a copy, regardless of the input.</p> <div class="admonition warning"> <p class=admonition-title>A borrowed document depends on your buffer</p> <p>If a document borrows its text, that text <strong>must outlive the document</strong> (and every view taken from it) and must stay <strong>unmodified</strong> for as long as the document exists, since floating-point values and unescaped strings are read from it lazily. Reading or writing through a view after the underlying buffer is gone is undefined behavior, exactly as it would be for a dangling <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string_view</span></code>.</p> </div> <p>A view is valid only while all of the following hold:</p> <ul> <li>the document is alive,</li> <li>the document has not been re-parsed since the view was taken (with <a href=../../api/basic_json_document/read/ ><code>read()</code></a> or <a href=../../api/basic_json_document/parse/ ><code>parse()</code></a> into it),</li> <li>the document has not had <a href=../../api/basic_json_document/shrink_to_fit/ ><code>shrink_to_fit()</code></a> called on it since, and</li> <li>if the document borrows its source text, that text is still alive and unmodified.</li> </ul> <p>Moving the <code>basic_json_document&lt;&gt;</code> itself is fine and does <strong>not</strong> invalidate its views: the index is a separate heap allocation that keeps its address across the move. Take a fresh view from <a href=../../api/basic_json_document/root/ ><code>root()</code></a> whenever any of the other conditions above was not met.</p> <div class=nj-fig-wrap> <p><svg class="nj-fig nj-jsonview " viewbox="0 0 840 572" role=img aria-labelledby="fig-jvt-title fig-jvt-title-d" xmlns=http://www.w3.org/2000/svg> <title id=fig-jvt-title>When a json_view becomes invalid</title> <desc id=fig-jvt-title-d>Four timelines. First: a document borrows a std::string; when the string is destroyed, the document and every view taken from it dangle. Second: doc.read() re-parses the document; views taken before are invalid, a fresh view from root() is valid. Third: doc.shrink_to_fit() has the same effect. Fourth: moving the document does not invalidate its views; destroying the moved-to document does.</desc> <defs> <marker id=jvt-bad viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-bad nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> </defs> <rect x=210 y=12 width=34 height=12 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <text class=nj-jsonview-note x=252 y=23 xml:space=preserve>alive / valid</text> <rect class=nj-jsonview-bad x=370 y=12 width=34 height=12 rx=3 /> <text class=nj-jsonview-note x=412 y=23 xml:space=preserve>dangling: using it is undefined behavior</text> <path class="nj-jsonview-arr nj-jsonview-c-line" d="M210 44 L820 44"/> <text class=nj-jsonview-tiny x=820 y=38 text-anchor=end xml:space=preserve>time →</text> <text class="nj-jsonview-h nj-jsonview-sm2" x=16 y=74 xml:space=preserve>The borrowed text is destroyed</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=99 text-anchor=end xml:space=preserve>std::string text</text> <rect x=210 y=87 width=260 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=127 text-anchor=end xml:space=preserve>json_document doc</text> <rect x=270 y=115 width=200 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <rect class=nj-jsonview-bad x=470 y=115 width=350 height=16 rx=3 /> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=155 text-anchor=end xml:space=preserve>json_view v</text> <rect x=330 y=143 width=140 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <rect class=nj-jsonview-bad x=470 y=143 width=350 height=16 rx=3 /> <path class=nj-jsonview-evt d="M470 82 V168"/> <text class="nj-jsonview-tiny nj-jsonview-c-bad" x=474 y=80 xml:space=preserve>text destroyed</text> <text class="nj-jsonview-note nj-jsonview-onbad" x=476 y=155 xml:space=preserve>every view, and the document itself</text> <text class="nj-jsonview-h nj-jsonview-sm2" x=16 y=202 xml:space=preserve>The document is re-parsed</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=227 text-anchor=end xml:space=preserve>json_document doc</text> <rect x=210 y=215 width=610 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=255 text-anchor=end xml:space=preserve>json_view v</text> <rect x=270 y=243 width=200 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <rect class=nj-jsonview-bad x=470 y=243 width=350 height=16 rx=3 /> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=283 text-anchor=end xml:space=preserve>v = doc.root()</text> <rect x=530 y=271 width=290 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <path class=nj-jsonview-evt d="M470 210 V296"/> <text class="nj-jsonview-tiny nj-jsonview-c-bad" x=474 y=208 xml:space=preserve>doc.read(other)</text> <text class="nj-jsonview-note nj-jsonview-onbad" x=476 y=255 xml:space=preserve>views taken before</text> <text class="nj-jsonview-note nj-jsonview-onok" x=536 y=283 xml:space=preserve>a fresh view is valid again</text> <text class="nj-jsonview-h nj-jsonview-sm2" x=16 y=330 xml:space=preserve>The document is shrunk</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=355 text-anchor=end xml:space=preserve>json_document doc</text> <rect x=210 y=343 width=610 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=383 text-anchor=end xml:space=preserve>json_view v</text> <rect x=270 y=371 width=200 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <rect class=nj-jsonview-bad x=470 y=371 width=350 height=16 rx=3 /> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=411 text-anchor=end xml:space=preserve>v = doc.root()</text> <rect x=530 y=399 width=290 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <path class=nj-jsonview-evt d="M470 338 V424"/> <text class="nj-jsonview-tiny nj-jsonview-c-bad" x=474 y=336 xml:space=preserve>doc.shrink_to_fit()</text> <text class="nj-jsonview-note nj-jsonview-onbad" x=476 y=383 xml:space=preserve>views taken before</text> <text class="nj-jsonview-note nj-jsonview-onok" x=536 y=411 xml:space=preserve>a fresh view is valid again</text> <text class="nj-jsonview-h nj-jsonview-sm2" x=16 y=458 xml:space=preserve>The document is moved, then destroyed</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=483 text-anchor=end xml:space=preserve>json_document doc</text> <rect x=210 y=471 width=210 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=511 text-anchor=end xml:space=preserve>moved = std::move(doc)</text> <rect x=420 y=499 width=260 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <text class="nj-jsonview-mono nj-jsonview-sm" x=198 y=539 text-anchor=end xml:space=preserve>json_view v</text> <rect x=270 y=527 width=410 height=16 rx=3 class="nj-jsonview-bar nj-jsonview-c-struct"/> <rect class=nj-jsonview-bad x=680 y=527 width=140 height=16 rx=3 /> <path class="nj-jsonview-evt nj-jsonview-evt--ok" d="M420 466 V552"/> <text class=nj-jsonview-tiny x=424 y=464 xml:space=preserve>std::move: views stay valid</text> <path class=nj-jsonview-evt d="M680 466 V552"/> <text class="nj-jsonview-tiny nj-jsonview-c-bad" x=684 y=464 xml:space=preserve>moved is destroyed</text> </svg></p> </div> <p class=nj-caption>Four timelines of a document and its views, each bar showing when an object is alive or valid and when it dangles. Destroying the borrowed text, re-parsing, or shrinking the document invalidates the views taken before; moving the document does not.</p> <p>A view can dangle, exactly like a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string_view</span></code>: nothing stops you from using it after its document is gone. This is deliberate. A view is two pointers and trivially copyable; making it safe (a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>shared_ptr</span></code> in the document and a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>weak_ptr</span></code> in each view) would make it larger, add reference counting to every copy, and a <code>lock()</code> to every access — exactly the costs the view exists to avoid. What is caught is the obvious case: because a view dies with its document, <a href=../../api/basic_json_document/root/ ><code>root()</code></a> is not callable on a temporary document: <code class=highlight><span class=k>auto</span><span class=w> </span><span class=n>v</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json_document</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>text</span><span class=p>).</span><span class=n>root</span><span class=p>();</span></code> does not compile. Give the document a name first.</p> <details class=example> <summary>Example: borrowed and owned documents, and when views become invalid</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;string&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;utility&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json_document</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=p>;</span>
<span class=w> </span><span class=c1>// BORROWED: doc only points into `text`; `text` must outlive `doc`</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=w> </span><span class=n>text</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"a": 1}</span><span class=dl>)</span><span class=s>"</span><span class=p>;</span>
<span class=w> </span><span class=n>json_document</span><span class=w> </span><span class=n>doc</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json_document</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>text</span><span class=p>);</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>doc</span><span class=p>.</span><span class=n>owns_source</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span><span class=w> </span><span class=c1>// false</span>
<span class=w> </span><span class=c1>// a view is valid as long as the document is alive, has not been</span>
<span class=w> </span><span class=c1>// re-parsed (read()) or shrunk (shrink_to_fit()), and -- if borrowed --</span>
<span class=w> </span><span class=c1>// the source text is alive</span>
<span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json_view</span><span class=w> </span><span class=n>v</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>doc</span><span class=p>.</span><span class=n>root</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>v</span><span class=p>.</span><span class=n>is_object</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// re-parsing the SAME document invalidates views taken before the call;</span>
<span class=w> </span><span class=c1>// `v` above must not be used after this line</span>
<span class=w> </span><span class=n>doc</span><span class=p>.</span><span class=n>read</span><span class=p>(</span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>[1, 2, 3]</span><span class=dl>)</span><span class=s>"</span><span class=p>);</span>
<span class=w> </span><span class=n>v</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>doc</span><span class=p>.</span><span class=n>root</span><span class=p>();</span><span class=w> </span><span class=c1>// take a fresh view instead</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>v</span><span class=p>.</span><span class=n>is_array</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// moving the document does not invalidate views: the node index is</span>
<span class=w> </span><span class=c1>// heap-allocated and does not move with the document object</span>
<span class=w> </span><span class=n>json_document</span><span class=w> </span><span class=n>moved</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>move</span><span class=p>(</span><span class=n>doc</span><span class=p>);</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>v</span><span class=p>.</span><span class=n>is_array</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>false</span>
<span class=kc>true</span>
<span class=kc>true</span>
<span class=kc>true</span>
</code></pre></div> </details> <h2 id=what-is-the-same-as-parse>What is the same as <code>parse()</code><a class=headerlink href=#what-is-the-same-as-parse title="Permanent link">&para;</a></h2> <ul> <li><strong>Accept/reject.</strong> <a href=../../api/basic_json_document/accept/ ><code>accept()</code></a> and <a href=../../api/basic_json_document/parse/ ><code>parse()</code></a> accept and reject exactly the same inputs as <a href=../../api/basic_json/accept/ ><code>basic_json::accept()</code></a>/<a href=../../api/basic_json/parse/ ><code>basic_json::parse()</code></a>, with the same <code>ignore_comments</code> and <code>ignore_trailing_commas</code> options.</li> <li><strong>Errors.</strong> A failing parse throws the same exception — the same id, message, and position — because on failure the library's own parser is run on the same bytes to produce the diagnostic. Valid input never pays for this, and the replay builds no values: it costs about a lexing pass up to the error. <code class=highlight><span class=n>allow_exceptions</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=nb>false</span></code> skips the replay and gives a <a href=../../api/basic_json_document/is_discarded/ >discarded</a> document instead of throwing, just as it gives a discarded value for <code class=highlight><span class=n>basic_json</span><span class=o>::</span><span class=n>parse</span><span class=p>()</span></code>.</li> <li><strong>Number classification.</strong> An integer literal that does not fit into the 64-bit integer type becomes a floating-point value, exactly as it does for <code class=highlight><span class=n>basic_json</span><span class=o>::</span><span class=n>parse</span><span class=p>()</span></code>.</li> <li><strong>Macros.</strong> <a href=../../api/macros/json_strict_nul_handling/ ><code>JSON_STRICT_NUL_HANDLING</code></a> and <a href=../../api/macros/json_noexception/ ><code>JSON_NOEXCEPTION</code></a>/<a href=../../api/macros/json_throw_user/ ><code>JSON_THROW_USER</code></a> behave the same way they do for <code>&lt;nlohmann/json.hpp&gt;</code>. These are the macros that change what the parser accepts or how it reports errors. The others either do not apply (<a href=../../api/macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a> needs parent pointers in <code>basic_json</code> values) or only affect the values <code>materialize()</code> produces, through <code>BasicJsonType</code>.</li> </ul> <h2 id=what-is-different>What is different<a class=headerlink href=#what-is-different title="Permanent link">&para;</a></h2> <ul> <li><strong>Only 64-bit integers.</strong> <code>basic_json_document&lt;BasicJsonType&gt;</code> requires <code>BasicJsonType::number_integer_t</code> and <code>number_unsigned_t</code> to both be 64 bits wide; this is a compile-time <code class=highlight><span class=k>static_assert</span></code>.</li> <li><strong>A 4 <abbr title="Gibibyte (2^30 bytes)">GiB</abbr> input limit.</strong> An input of 4294967280 bytes (4 <abbr title="Gibibyte (2^30 bytes)">GiB</abbr> minus 16 bytes) or more throws <a href=../../home/exceptions/#jsonexceptionout_of_range416><code>out_of_range.416</code></a>, a limit <code class=highlight><span class=n>basic_json</span><span class=o>::</span><span class=n>parse</span><span class=p>()</span></code> does not have. It keeps an index entry at 16 bytes: offsets and counts are 32 bits wide. The limit is 16 bytes below 2^32, because the parser reads in 16-byte steps, and a position one step past the end must still fit.</li> <li><strong>A stream is always read to its end.</strong> There is no partial/streaming read of an <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>istream</span></code>: the stream is read to its end into a buffer the document owns, and parsing starts after that.</li> <li><strong>No source positions on <code>materialize()</code>.</strong> Even with <a href=../../api/macros/json_diagnostic_positions/ ><code>JSON_DIAGNOSTIC_POSITIONS</code></a> enabled, <a href=../../api/basic_json_view/materialize/ ><code>materialize()</code></a> does not set them. The index has the start offset of every value, but not the end of arrays, objects, and escaped strings, which the positions also need.</li> <li><strong>Objects iterate in document order.</strong> <a href=../../api/basic_json_view/begin/ ><code>begin()</code></a>/ <a href=../../api/basic_json_view/end/ ><code>end()</code></a> and <a href=../../api/basic_json_view/items/ ><code>items()</code></a> visit an object's members in the order they appear in the source text. <code>basic_json</code>'s default <code>object_t</code> is a <code>std::map</code>, which sorts by key, so iterating a <a href=../../api/basic_json_view/materialize/ ><code>materialize()</code></a>d value can print members in a different order than iterating the view they came from.</li> <li><strong>Chained access is safe.</strong> <a href=../../api/basic_json_view/operator%5B%5D/ ><code>operator[]</code></a> with a missing key, an index out of range, or an unresolvable <abbr title="JavaScript Object Notation">JSON</abbr> pointer returns a <a href=../../api/basic_json_view/is_discarded/ >discarded</a> view, and <code>operator[]</code> on a discarded view returns a discarded view without throwing: <code class=highlight><span class=n>v</span><span class=p>[</span><span class=s>"a"</span><span class=p>][</span><span class=s>"b"</span><span class=p>][</span><span class=mi>0</span><span class=p>]</span></code> can be tested once at the end. Type errors on values that exist (a key on an array, an index on an object) still throw, and <a href=../../api/basic_json_view/at/ ><code>at</code></a> throws for every missing value.</li> <li><strong>Duplicate keys: lookups find the first member, <code>parse()</code> keeps the last.</strong> See <a href=#duplicate-keys>Duplicate keys</a> below.</li> <li><strong>No <a href=../../api/macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a> path.</strong> Exceptions thrown by <code>basic_json_view</code>'s own element access and lookup functions never carry the <abbr title="JavaScript Object Notation">JSON</abbr> Pointer path <code>JSON_DIAGNOSTICS</code> would otherwise add: the view has no <code>basic_json</code> value to point at, so the exception is created without one, regardless of how <code>BasicJsonType</code> was built.</li> <li><strong>Ordering comparisons are not provided</strong> by <code>basic_json_view</code> — there is no <code class=highlight><span class=k>operator</span><span class=o>&lt;</span></code>. <a href=../../api/basic_json_view/operator_eq/ ><code>operator==</code></a> and <a href=../../api/basic_json_view/operator_ne/ ><code>operator!=</code></a> are provided, though: two views, or a view and a <code>BasicJsonType</code> value, compare equal exactly when <a href=../../api/basic_json_view/materialize/ ><code>materialize()</code></a> or <a href=../../api/basic_json/parse/ ><code>parse()</code></a> would produce equal values for them, without ever building a tree to do it. For ordering, too, <a href=../../api/basic_json_view/materialize/ ><code>materialize()</code></a> is the way to get a value you can compare.</li> </ul> <h2 id=duplicate-keys>Duplicate keys<a class=headerlink href=#duplicate-keys title="Permanent link">&para;</a></h2> <div class="admonition warning"> <p class=admonition-title>A lookup in a view and in the parsed value can give different answers</p> <p>If an object in the source text repeats a key, <a href=../../api/basic_json_view/operator%5B%5D/ ><code>operator[]</code></a>, <a href=../../api/basic_json_view/at/ ><code>at</code></a>, <a href=../../api/basic_json_view/find/ ><code>find</code></a>, <a href=../../api/basic_json_view/value/ ><code>value</code></a>, <a href=../../api/basic_json_view/contains/ ><code>contains</code></a>, and <abbr title="JavaScript Object Notation">JSON</abbr> pointer resolution all return the <strong>first</strong> member with that key. <code>basic_json::parse()</code> instead keeps the <strong>last</strong> value of a repeated key, so for <code class=highlight><span class=p>{</span><span class=s>"a"</span><span class=o>:</span><span class=mi>1</span><span class=p>,</span><span class=s>"a"</span><span class=o>:</span><span class=mi>2</span><span class=p>}</span></code>, <code class=highlight><span class=n>view</span><span class=p>[</span><span class=s>"a"</span><span class=p>]</span></code> is <code class=highlight><span class=mi>1</span></code> while <code class=highlight><span class=n>parse</span><span class=p>(</span><span class=n>text</span><span class=p>)[</span><span class=s>"a"</span><span class=p>]</span></code> is <code class=highlight><span class=mi>2</span></code>. <a href=../../api/basic_json_view/count/ ><code>count</code></a> counts every member with the key, so it is <code class=highlight><span class=mi>2</span></code> here.</p> </div> <p><a href=../../api/basic_json_view/begin/ ><code>begin()</code></a>/<a href=../../api/basic_json_view/end/ ><code>end()</code></a> and <a href=../../api/basic_json_view/items/ ><code>items()</code></a> visit <em>every</em> occurrence, in document order, and <a href=../../api/basic_json_view/size/ ><code>size()</code></a> counts all of them, so <code class=highlight><span class=n>view</span><span class=p>.</span><span class=n>size</span><span class=p>()</span></code> can be larger than <code class=highlight><span class=n>view</span><span class=p>.</span><span class=n>materialize</span><span class=p>().</span><span class=n>size</span><span class=p>()</span></code>.</p> <p><strong>Why the first?</strong> A lookup can stop as soon as it finds a match. Returning the last member would force every lookup to scan all members of the object, even when the key is found at the very first one: this made lookups in small objects 1.6 to 3.4 times slower. The hash index of the keys of objects with 128 members or more leads to the first member of a key as well. Other zero-copy parsers that index the source text, such as yyjson and simdjson, also return the first member. <abbr title="Request for Comments">RFC</abbr> 8259 only says that names within an object SHOULD be unique and that the behavior of a receiver that sees duplicates is unpredictable, so neither choice is wrong.</p> <p>The same holds for <a href=../../api/basic_json_view/get/ ><code>get&lt;T&gt;()</code></a> of a type whose <code>from_json()</code> reads the view, such as the types of the <code>NLOHMANN_DEFINE_TYPE_*</code> macros: their members are looked up, so <code class=highlight><span class=n>get</span><span class=o>&lt;</span><span class=n>point</span><span class=o>&gt;</span><span class=p>()</span></code> of <code class=highlight><span class=p>{</span><span class=s>"x"</span><span class=o>:</span><span class=mi>1</span><span class=p>,</span><span class=s>"x"</span><span class=o>:</span><span class=mi>2</span><span class=p>}</span></code> reads <code class=highlight><span class=n>x</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=mi>1</span></code>, while <code class=highlight><span class=n>materialize</span><span class=p>().</span><span class=n>get</span><span class=o>&lt;</span><span class=n>point</span><span class=o>&gt;</span><span class=p>()</span></code> reads <code class=highlight><span class=mi>2</span></code>.</p> <p><strong>What stays the same as <code>parse()</code>?</strong> <a href=../../api/basic_json_view/materialize/ ><code>materialize()</code></a> and <a href=../../api/basic_json_view/get/ ><code>get&lt;std::map&lt;...&gt;&gt;()</code></a> replay every member in order, so they keep the <em>last</em> value exactly like <code class=highlight><span class=n>basic_json</span><span class=o>::</span><span class=n>parse</span><span class=p>()</span></code> (at the position of the first occurrence of the key, for an <a href=../../api/ordered_json/ ><code>ordered_json</code></a>).</p> <p><strong>How do I get the value <code>parse()</code> would give?</strong> Either call <code class=highlight><span class=n>view</span><span class=p>.</span><span class=n>materialize</span><span class=p>()</span></code> and look the key up in the result, or iterate the members and keep the last match:</p> <div class=highlight><pre><span></span><code><span class=c1>// the last member with the key "a", as parse() would keep it</span>
<span class=n>json_view</span><span class=w> </span><span class=n>last</span><span class=p>;</span>
<span class=k>for</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>item</span><span class=w> </span><span class=o>:</span><span class=w> </span><span class=n>view</span><span class=p>.</span><span class=n>items</span><span class=p>())</span>
<span class=p>{</span>
<span class=w> </span><span class=k>if</span><span class=w> </span><span class=p>(</span><span class=n>item</span><span class=p>.</span><span class=n>key</span><span class=p>()</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=s>"a"</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>last</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>item</span><span class=p>.</span><span class=n>value</span><span class=p>();</span>
<span class=w> </span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> <p>If you cannot trust the source text to have unique keys, check <a href=../../api/basic_json_view/size/ ><code>size()</code></a> against the number of distinct keys, or reject duplicates when iterating.</p> <h2 id=getting-values-out-without-copying>Getting values out without copying<a class=headerlink href=#getting-values-out-without-copying title="Permanent link">&para;</a></h2> <p><a href=../../api/basic_json_view/get/ ><code>get&lt;T&gt;()</code></a> converts most <code>T</code> directly from the flat index, without ever building a <code>basic_json</code> value for the conversion: <code class=highlight><span class=kt>bool</span></code>, arithmetic types, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>nullptr_t</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>/other <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>basic_string</span></code>s (copied once), <code>basic_json_view</code> itself, the standard containers and other types the library converts (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>map</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>list</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>array</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>pair</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>tuple</span></code>, <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>optional</span></code>, ...), and the types of the <code>NLOHMANN_DEFINE_TYPE_*</code> and <code>NLOHMANN_JSON_SERIALIZE_ENUM</code> macros. Types whose <code>from_json()</code> is written for <code>basic_json</code> only go through <a href=../../api/basic_json_view/materialize/ ><code>materialize()</code></a><code>.get&lt;T&gt;()</code> instead: the subtree is built into a real <code>basic_json</code> value first, exactly as <a href=../../api/basic_json/parse/ ><code>parse()</code></a> would, and converted from there. See <a href=#writing-generic-code>Writing generic code</a> for how to write a <code>from_json()</code> that reads views.</p> <p>Two conversions never copy at all:</p> <ul> <li><a href=../../api/basic_json_view/get_string/ ><code>get_string()</code></a> (equivalently, <code class=highlight><span class=n>get</span><span class=o>&lt;</span><span class=n>string_view_t</span><span class=o>&gt;</span><span class=p>()</span></code>) returns a string as a <code>string_view_t</code> pointing into the document's <a href=../../api/basic_json_document/source/ ><code>source()</code></a> text — or, for a string that contains escape sequences, into the document's own buffer of decoded strings — instead of allocating a new <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code>.</li> <li><a href=../../api/basic_json_view/number_token/ ><code>number_token()</code></a> returns a number exactly as it was written in the source, e.g. <code class=highlight><span class=s>"1.50"</span></code>, <code class=highlight><span class=s>"1E2"</span></code>, or an integer with more digits than any number type holds, instead of rounding it into a <code class=highlight><span class=kt>double</span></code>/<code class=highlight><span class=kt>int64_t</span></code> the way <code class=highlight><span class=n>get</span><span class=o>&lt;</span><span class=n>T</span><span class=o>&gt;</span><span class=p>()</span></code> (and <a href=../../api/basic_json/parse/ ><code>basic_json::parse()</code></a>) would.</li> </ul> <p>Both results are only valid as long as the view — and, for a string with no escapes, the borrowed source text — is.</p> <h2 id=writing-generic-code>Writing generic code<a class=headerlink href=#writing-generic-code title="Permanent link">&para;</a></h2> <p>A view's type names its <code>BasicJsonType</code> and its <a href=../../api/view_mode/ ><code>view_mode</code></a>: <a href=../../api/json_view/ ><code>json_view</code></a> is <code class=highlight><span class=n>basic_json_view</span><span class=o>&lt;</span><span class=n>json</span><span class=p>,</span><span class=w> </span><span class=n>view_mode</span><span class=o>::</span><span class=n>read_only</span><span class=o>&gt;</span></code>, and <a href=../../api/json_editable_view/ ><code>json_editable_view</code></a> is <code class=highlight><span class=n>basic_json_view</span><span class=o>&lt;</span><span class=n>json</span><span class=p>,</span><span class=w> </span><span class=n>view_mode</span><span class=o>::</span><span class=n>editable</span><span class=o>&gt;</span></code>. These are different types. The only conversion between them turns a view of a read-only document into a view of an editable document of the same <code>BasicJsonType</code>, so a function written for one shortcut accepts few other views:</p> <div class=highlight><pre><span></span><code><span class=kt>void</span><span class=w> </span><span class=nf>print_names</span><span class=p>(</span><span class=n>json_view</span><span class=w> </span><span class=n>v</span><span class=p>);</span><span class=w> </span><span class=c1>// accepts neither an ordered_json_view nor a json_editable_view</span>
<span class=kt>void</span><span class=w> </span><span class=nf>print_names</span><span class=p>(</span><span class=n>json_editable_view</span><span class=w> </span><span class=n>v</span><span class=p>);</span><span class=w> </span><span class=c1>// also accepts a json_view, but no ordered_json_view</span>
</code></pre></div> <p>This is the same pitfall as a <code>to_json</code>/<code>from_json</code> written for <code>json</code> instead of any <code>BasicJsonType</code>, which then does not work for <code>ordered_json</code>. The shortcuts are for declaring documents and views; a function that takes a view names the views it accepts with a template:</p> <div class=highlight><pre><span></span><code><span class=c1>// views of editable documents only</span>
<span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=o>&gt;</span>
<span class=kt>void</span><span class=w> </span><span class=n>f</span><span class=p>(</span><span class=n>basic_json_view</span><span class=o>&lt;</span><span class=n>BasicJsonType</span><span class=p>,</span><span class=w> </span><span class=n>view_mode</span><span class=o>::</span><span class=n>editable</span><span class=o>&gt;</span><span class=w> </span><span class=n>v</span><span class=p>);</span>
<span class=c1>// views of read-only documents only</span>
<span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=o>&gt;</span>
<span class=kt>void</span><span class=w> </span><span class=n>f</span><span class=p>(</span><span class=n>basic_json_view</span><span class=o>&lt;</span><span class=n>BasicJsonType</span><span class=p>,</span><span class=w> </span><span class=n>view_mode</span><span class=o>::</span><span class=n>read_only</span><span class=o>&gt;</span><span class=w> </span><span class=n>v</span><span class=p>);</span>
<span class=c1>// views of either document type</span>
<span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=p>,</span><span class=w> </span><span class=n>view_mode</span><span class=w> </span><span class=n>Mode</span><span class=o>&gt;</span>
<span class=kt>void</span><span class=w> </span><span class=n>f</span><span class=p>(</span><span class=n>basic_json_view</span><span class=o>&lt;</span><span class=n>BasicJsonType</span><span class=p>,</span><span class=w> </span><span class=n>Mode</span><span class=o>&gt;</span><span class=w> </span><span class=n>v</span><span class=p>);</span>
</code></pre></div> <p>Views are passed by value: they are two pointers, cheap to copy, like a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string_view</span></code>. A <code>const&amp;</code> works as well, but a non-<code>const</code> reference does not bind to the views that <a href=../../api/basic_json_document/root/ ><code>root()</code></a>, <a href=../../api/basic_json_view/operator%5B%5D/ ><code>operator[]</code></a>, and <a href=../../api/basic_json_view/at/ ><code>at()</code></a> return, so <code class=highlight><span class=n>f</span><span class=p>(</span><span class=n>doc</span><span class=p>.</span><span class=n>root</span><span class=p>())</span></code> would not compile.</p> <p>There is no conversion from an editable view to a read-only one, by design: the mode decides how a view walks the index. A read-only view reads a container in place, while a view of an editable document follows the links that edits leave behind, so a read-only view of an edited document would read stale values. The other direction is safe: a read-only document has no edits, so a view of it <a href=../../api/basic_json_view/basic_json_view/ >converts</a> to an editable view, which reads it like an editable document before its first edit. A template deduces the mode without conversions, so the template forms above still accept only the modes they name. Views of both modes compare with <a href=../../api/basic_json_view/operator_eq/ ><code>operator==</code></a>.</p> <p><a href=../../api/is_json_view/ ><code>is_json_view&lt;T&gt;</code></a> tells views from other types, for constraints that cannot be written as a <code>basic_json_view&lt;...&gt;</code> parameter.</p> <h3 id=a-from_json-that-reads-views>A <code>from_json()</code> that reads views<a class=headerlink href=#a-from_json-that-reads-views title="Permanent link">&para;</a></h3> <p><a href=../../api/basic_json_view/get/ ><code>get&lt;T&gt;()</code></a> on a view calls <code>T</code>'s <code>from_json()</code> with the view itself if that <code>from_json()</code> accepts views, and with <a href=../../api/basic_json_view/materialize/ ><code>materialize()</code></a> otherwise. The <code>from_json()</code> functions of the <a href=../../api/macros/nlohmann_define_type_intrusive/ ><code>NLOHMANN_DEFINE_TYPE_*</code></a>, <a href=../../api/macros/nlohmann_define_derived_type/ ><code>NLOHMANN_DEFINE_DERIVED_TYPE_*</code></a>, and <a href=../../api/macros/nlohmann_json_serialize_enum/ ><code>NLOHMANN_JSON_SERIALIZE_ENUM</code></a> macros, and those of the library for the standard types, accept views, so these types need nothing else. For decoding the statuses of twitter.json into structs, reading the view is about 5 times faster than <code class=highlight><span class=n>materialize</span><span class=p>().</span><span class=n>get</span><span class=o>&lt;</span><span class=n>T</span><span class=o>&gt;</span><span class=p>()</span></code>.</p> <p>A hand-written <code>from_json()</code> reads views if it is constrained to <code>json</code> values and views:</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=w> </span><span class=o>&lt;</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>J</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>std</span><span class=o>::</span><span class=n>enable_if</span><span class=w> </span><span class=o>&lt;</span>
<span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>is_json_view</span><span class=o>&lt;</span><span class=n>J</span><span class=o>&gt;::</span><span class=n>value</span><span class=w> </span><span class=o>||</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o>&lt;</span><span class=n>J</span><span class=p>,</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=o>&gt;::</span><span class=n>value</span><span class=p>,</span><span class=w> </span><span class=kt>int</span><span class=w> </span><span class=o>&gt;::</span><span class=n>type</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=mi>0</span><span class=w> </span><span class=o>&gt;</span>
<span class=kt>void</span><span class=w> </span><span class=n>from_json</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>J</span><span class=o>&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>person</span><span class=o>&amp;</span><span class=w> </span><span class=n>p</span><span class=p>)</span>
<span class=p>{</span>
<span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>name</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=s>"name"</span><span class=p>).</span><span class=k>template</span><span class=w> </span><span class=n>get</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>age</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>at</span><span class=p>(</span><span class=s>"age"</span><span class=p>).</span><span class=k>template</span><span class=w> </span><span class=n>get</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>();</span>
<span class=p>}</span>
</code></pre></div> <p>Its body may only use what views and <code>basic_json</code> have in common: the type checks, <code>at()</code>, <code>operator[]</code>, <code>contains()</code>, <code>value()</code>, <code>size()</code>, iteration and <code>items()</code>, and <code>get&lt;T&gt;()</code>/<code>get_to()</code>. An unconstrained <code class=highlight><span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=o>&gt;</span><span class=w> </span><span class=kt>void</span><span class=w> </span><span class=n>from_json</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>BasicJsonType</span><span class=o>&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>person</span><span class=o>&amp;</span><span class=w> </span><span class=n>p</span><span class=p>)</span></code>, as in <a href=../arbitrary_types/ >arbitrary type conversions</a>, is never called with a view, as it might use <code>basic_json</code> functions a view does not have; such a type is converted through <code>materialize()</code>. A <code>from_json()</code> for <code>json</code> only is converted through <code>materialize()</code> as well.</p> <p>Two things differ when a <code>from_json()</code> reads the view:</p> <ul> <li><strong>Duplicate keys.</strong> Members looked up by name (<code>at()</code>, <code>value()</code>, ... and thus the macros) find the <strong>first</strong> member with a repeated key, see <a href=#duplicate-keys>Duplicate keys</a>; <code class=highlight><span class=n>materialize</span><span class=p>().</span><span class=n>get</span><span class=o>&lt;</span><span class=n>T</span><span class=o>&gt;</span><span class=p>()</span></code> would see the last one. Containers built from an object, such as <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>map</span></code>, keep the <strong>last</strong> value either way, as <a href=../../api/basic_json/parse/ ><code>parse()</code></a> does.</li> <li><strong><a href=../../api/macros/json_diagnostics/ ><code>JSON_DIAGNOSTICS</code></a>.</strong> Exceptions thrown by the view carry no path to the value.</li> </ul> <p><code>to_json()</code> is unaffected: it writes <code>basic_json</code> values, never views.</p> <h2 id=writing-a-view-back>Writing a view back<a class=headerlink href=#writing-a-view-back title="Permanent link">&para;</a></h2> <p><a href=../../api/basic_json_view/dump/ ><code>dump()</code></a> serializes a view directly from the flat index, without ever building a <code>basic_json</code> value. An object's members are written in document order, not sorted by key, and <em>every</em> occurrence of a repeated key is written, not only the last one — the same two ways <a href=#what-is-different>iteration</a> already differs from a <a href=../../api/basic_json_view/materialize/ ><code>materialize()</code></a>d value, see <a href=#duplicate-keys>Duplicate keys</a>. <code class=highlight><span class=n>materialize</span><span class=p>().</span><span class=n>dump</span><span class=p>()</span></code> gives a different result in both respects for a <code>json_view</code>.</p> <p>By default, numbers are written the way <a href=../../api/basic_json/dump/ ><code>basic_json::dump()</code></a> would. <a href=../../api/basic_json_view/number_format/ ><code>number_format::source</code></a> instead copies every number exactly as it was written in the source text — a price like <code class=highlight><span class=mf>19.90</span></code>, a long order or account ID with more digits than any number type holds, or a high-precision coordinate — something <code>basic_json</code> cannot do at all, since parsing already reduces a number to its parsed <code class=highlight><span class=kt>double</span></code>/<code class=highlight><span class=kt>int64_t</span></code> value.</p> <p><a href=../../api/basic_json_view/operator_ltlt/ ><code>operator&lt;&lt;</code></a> writes a view to a stream the way <code>basic_json</code>'s does, using the stream's <code>width</code>/<code>fill</code> for indentation.</p> <h2 id=editing-a-document>Editing a document<a class=headerlink href=#editing-a-document title="Permanent link">&para;</a></h2> <p>Everything above is read-only: a <code>json_document</code>/<code>json_view</code> lets you look at a parsed text without copying it, but not change it. <a href=../../api/basic_json_document/ ><code>basic_json_document&lt;BasicJsonType, view_mode::editable&gt;</code></a> — more conveniently spelled <a href=../../api/json_editable_document/ ><code>json_editable_document</code></a> or <a href=../../api/ordered_json_editable_document/ ><code>ordered_json_editable_document</code></a> — also lets you <a href=../../api/basic_json_document/set/ ><code>set</code></a> a value, <a href=../../api/basic_json_document/push_back/ ><code>push_back</code></a> onto or <a href=../../api/basic_json_document/insert/ ><code>insert</code></a> into an array, and <a href=../../api/basic_json_document/erase/ ><code>erase</code></a> an object member or an array element, still without ever building a <code>basic_json</code> tree for parts you do not touch.</p> <p>The <a href=../../api/view_mode/ >mode</a> defaults to <code class=highlight><span class=n>view_mode</span><span class=o>::</span><span class=n>read_only</span></code>, so <code>json_document</code>/<code>ordered_json_document</code> are unaffected — they carry none of the bookkeeping edits need, and calling <code>set</code>/<code>push_back</code>/<code>insert</code>/<code>erase</code> on one is a compile error, not a runtime one.</p> <h3 id=why-editing-without-reformatting>Why: editing without reformatting<a class=headerlink href=#why-editing-without-reformatting title="Permanent link">&para;</a></h3> <p>The <code class=highlight><span class=mf>19.90</span></code> price from <a href=#writing-a-view-back>above</a> is exactly the kind of value that makes editing a <code>json</code> or <code>ordered_json</code> value in place lossy. Say you parse a configuration file, patch one field, and write it back:</p> <ul> <li><strong><code>json</code></strong> re-sorts every key on the way in (<code>object_t</code> is a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>map</span></code>) and rewrites every number to its shortest round-trip form on the way out — a one-field patch turns into a diff that reorders the whole file and rewrites <code class=highlight><span class=mf>19.90</span></code> to <code class=highlight><span class=mf>19.9</span></code>.</li> <li><strong><code>ordered_json</code></strong> keeps the key order, but still rewrites every number the same way: parsing has already reduced it to a <code class=highlight><span class=kt>double</span></code>/<code class=highlight><span class=kt>int64_t</span></code>, and there is no way back to how it was spelled in the source text.</li> </ul> <p>The patch of the example below (set <code>"host"</code>, add <code>"retries"</code>) written back by each of them:</p> <div class=nj-jsonview-cmp role=group aria-label="The same patch written back by json, ordered_json, and json_editable_document"> <div><p class=nj-jsonview-cmp-h><code>json</code></p><p class=nj-jsonview-cmp-v>keys sorted, numbers rewritten</p><pre>{<span class=nj-jsonview-bad>"host"</span>:"db2",
"name":"cache",
"port":6379,
"price":<span class=nj-jsonview-bad>19.9</span>,
"retries":3}</pre></div> <div><p class=nj-jsonview-cmp-h><code>ordered_json</code></p><p class=nj-jsonview-cmp-v>key order kept, numbers rewritten</p><pre>{"name":"cache",
"host":"db2",
"port":6379,
"price":<span class=nj-jsonview-bad>19.9</span>,
"retries":3}</pre></div> <div class=nj-jsonview-cmp--best><p class=nj-jsonview-cmp-h><code>json_editable_document</code></p><p class=nj-jsonview-cmp-v>order and spelling kept</p><pre>{"name":"cache",
"host":"db2",
"port":6379,
"price":<span class=nj-jsonview-ok>19.90</span>,
"retries":3}</pre></div> </div> <p>An editable document keeps both. <a href=../../api/basic_json_view/dump/ ><code>dump()</code></a> of an edited document writes members in document order — a member <a href=../../api/basic_json_document/set/ ><code>set</code></a> added goes at the end, exactly where it was inserted, and an <a href=../../api/basic_json_document/erase/ ><code>erase</code></a>d member simply leaves a gap: everything around it keeps its place — and <a href=../../api/basic_json_view/number_format/ ><code>number_format::source</code></a> keeps the exact spelling of every number an edit did not itself touch; a number an edit <em>did</em> touch is written the way <a href=../../api/basic_json/dump/ ><code>BasicJsonType::dump()</code></a> would write it, since there is no source spelling for a brand new value.</p> <details class=example> <summary>Example: patch a configuration, keeping member order and number spellings</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json_editable_document</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json_editable_view</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=c1>// a configuration file, as it might be read from disk</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=w> </span><span class=n>text</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"name": "cache", "host": "db1", "port": 6379, "price": 19.90}</span><span class=dl>)</span><span class=s>"</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>text</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"</span><span class=se>\n\n</span><span class=s>"</span><span class=p>;</span>
<span class=w> </span><span class=c1>// patch two fields -- "price" is never touched</span>
<span class=w> </span><span class=n>json_editable_document</span><span class=w> </span><span class=n>doc</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json_editable_document</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>text</span><span class=p>);</span>
<span class=w> </span><span class=n>doc</span><span class=p>.</span><span class=n>set</span><span class=p>(</span><span class=n>doc</span><span class=p>.</span><span class=n>root</span><span class=p>(),</span><span class=w> </span><span class=s>"host"</span><span class=p>,</span><span class=w> </span><span class=s>"db2"</span><span class=p>);</span>
<span class=w> </span><span class=n>doc</span><span class=p>.</span><span class=n>set</span><span class=p>(</span><span class=n>doc</span><span class=p>.</span><span class=n>root</span><span class=p>(),</span><span class=w> </span><span class=s>"retries"</span><span class=p>,</span><span class=w> </span><span class=mi>3</span><span class=p>);</span>
<span class=w> </span><span class=c1>// member order (the new member at the end) and the untouched number's</span>
<span class=w> </span><span class=c1>// exact spelling survive</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>doc</span><span class=p>.</span><span class=n>root</span><span class=p>().</span><span class=n>dump</span><span class=p>(</span><span class=mi>-1</span><span class=p>,</span><span class=w> </span><span class=sc>' '</span><span class=p>,</span><span class=w> </span><span class=nb>false</span><span class=p>,</span><span class=w> </span><span class=n>json_editable_view</span><span class=o>::</span><span class=n>number_format</span><span class=o>::</span><span class=n>source</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// the same patch on a plain json value: keys are sorted (object_t is a</span>
<span class=w> </span><span class=c1>// std::map), and "price" is rewritten even though the patch never</span>
<span class=w> </span><span class=c1>// touched it</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>plain</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>text</span><span class=p>);</span>
<span class=w> </span><span class=n>plain</span><span class=p>[</span><span class=s>"host"</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>"db2"</span><span class=p>;</span>
<span class=w> </span><span class=n>plain</span><span class=p>[</span><span class=s>"retries"</span><span class=p>]</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=mi>3</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>plain</span><span class=p>.</span><span class=n>dump</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>{</span><span class=nt>"name"</span><span class=p>:</span><span class=w> </span><span class=s2>"cache"</span><span class=p>,</span><span class=w> </span><span class=nt>"host"</span><span class=p>:</span><span class=w> </span><span class=s2>"db1"</span><span class=p>,</span><span class=w> </span><span class=nt>"port"</span><span class=p>:</span><span class=w> </span><span class=mi>6379</span><span class=p>,</span><span class=w> </span><span class=nt>"price"</span><span class=p>:</span><span class=w> </span><span class=mf>19.90</span><span class=p>}</span>
<span class=p>{</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"cache"</span><span class=p>,</span><span class=nt>"host"</span><span class=p>:</span><span class=s2>"db2"</span><span class=p>,</span><span class=nt>"port"</span><span class=p>:</span><span class=mi>6379</span><span class=p>,</span><span class=nt>"price"</span><span class=p>:</span><span class=mf>19.90</span><span class=p>,</span><span class=nt>"retries"</span><span class=p>:</span><span class=mi>3</span><span class=p>}</span>
<span class=p>{</span><span class=nt>"host"</span><span class=p>:</span><span class=s2>"db2"</span><span class=p>,</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"cache"</span><span class=p>,</span><span class=nt>"port"</span><span class=p>:</span><span class=mi>6379</span><span class=p>,</span><span class=nt>"price"</span><span class=p>:</span><span class=mf>19.9</span><span class=p>,</span><span class=nt>"retries"</span><span class=p>:</span><span class=mi>3</span><span class=p>}</span>
</code></pre></div> </details> <h3 id=what-stays-valid-and-what-an-edit-costs>What stays valid, and what an edit costs<a class=headerlink href=#what-stays-valid-and-what-an-edit-costs title="Permanent link">&para;</a></h3> <p>The source text itself is <strong>never written</strong>, and the parsed index never moves — a value keeps the node it was parsed into for as long as it is not itself replaced. So every <a href=../../api/basic_json_view/ >view</a> taken before an edit, including a previously obtained <a href=../../api/basic_json_document/root/ ><code>root()</code></a>, stays valid and, if it still refers to the edited value, sees the edit; a view of a value a later edit drops or replaces just keeps showing what it last held. New values go to storage the document allocates and owns on demand. The one thing an edit does invalidate is the <strong>iterators</strong> taken over an edited array or object: the first time an element is added to it, inserted into it, erased from it, or replaced by a value that spans a different number of nodes, its elements move from the parsed, fixed layout to a growable block of links so that <a href=../../api/basic_json_document/push_back/ ><code>push_back</code></a> can later grow it in amortized constant time — existing elements are not touched, but an iterator that was walking the old layout no longer matches. A string obtained with <a href=../../api/basic_json_view/get_string/ ><code>get_string()</code></a> is unaffected either way and stays valid across further edits. See <a href=../../api/basic_json_document/#edits><code>basic_json_document</code>'s Edits</a> for the details, and <a href=../../api/basic_json_document/set/#exception-safety><code>set</code>'s Exception safety</a> for what an edit guarantees if it throws (the <em>basic</em> guarantee, not the strong one <code>dump()</code> and the read-only functions provide). How edits are kept in the index is described in the <a href=../../home/architecture/#node-index-of-json-views>architecture overview</a>.</p> <p>Step through the edits of a small document (the node fields follow the <a href=../../home/architecture/#node-index-of-json-views>architecture overview</a>):</p> <div class=nj-jsonview-steps data-nj-jsonview-steps> <figure class=nj-jsonview-step data-label="After parsing"> <div class=nj-jsonview-scroll> <svg class="nj-fig nj-jsonview nj-jsonview-editfig" viewbox="0 0 840 372" role=img aria-labelledby="fig-jve0-title fig-jve0-title-d" xmlns=http://www.w3.org/2000/svg> <title id=fig-jve0-title>Step 1 of 5: parsed</title> <desc id=fig-jve0-title-d>After parse: nine nodes, nothing owned yet. The dump with number_format::source is {&quot;port&quot;:6379,&quot;price&quot;:19.90,&quot;tags&quot;:[&quot;eu&quot;,&quot;a\&quot;b&quot;]}.</desc> <defs> <marker id=jve0-line viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-line nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve0-own viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-own nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve0-struct viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-struct nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve0-bad viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-bad nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> </defs> <text class="nj-jsonview-note nj-jsonview-strong" x=16 y=22 xml:space=preserve>parsed index: fixed, never moves</text> <text class=nj-jsonview-note x=824 y=22 text-anchor=end xml:space=preserve>the source text is never written</text> <rect x=36 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=42 y=47 xml:space=preserve>0</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=78 y=61 text-anchor=middle xml:space=preserve>object</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=78 y=77 text-anchor=middle xml:space=preserve>{ } 3</text> <rect x=124 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=130 y=47 xml:space=preserve>1</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=166 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=166 y=77 text-anchor=middle xml:space=preserve>port</text> <rect x=212 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=218 y=47 xml:space=preserve>2</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-num" x=254 y=61 text-anchor=middle xml:space=preserve>uint</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=254 y=77 text-anchor=middle xml:space=preserve>6379</text> <rect x=300 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=306 y=47 xml:space=preserve>3</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=342 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=342 y=77 text-anchor=middle xml:space=preserve>price</text> <rect x=388 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=394 y=47 xml:space=preserve>4</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-num" x=430 y=61 text-anchor=middle xml:space=preserve>float</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=430 y=77 text-anchor=middle xml:space=preserve>19.90</text> <rect x=476 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=482 y=47 xml:space=preserve>5</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=518 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=518 y=77 text-anchor=middle xml:space=preserve>tags</text> <rect x=564 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=570 y=47 xml:space=preserve>6</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=606 y=61 text-anchor=middle xml:space=preserve>array</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=606 y=77 text-anchor=middle xml:space=preserve>[ ] 2</text> <rect x=652 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-str"/> <text class=nj-jsonview-tiny x=658 y=47 xml:space=preserve>7</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-str" x=694 y=61 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=694 y=77 text-anchor=middle xml:space=preserve>&quot;eu&quot;</text> <rect x=740 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-dec"/> <text class=nj-jsonview-tiny x=746 y=47 xml:space=preserve>8</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-dec" x=782 y=61 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=782 y=77 text-anchor=middle xml:space=preserve>a&quot;b</text> <text class="nj-jsonview-note nj-jsonview-strong nj-jsonview-c-own" x=16 y=288 xml:space=preserve>owned storage: allocated on demand, never moves</text> <rect class=nj-jsonview-store x=10 y=192 width=820 height=54 rx=8 /> <text class=nj-jsonview-note x=26 y=224 xml:space=preserve>empty: a read-only json_document has none of this</text> <path class=nj-jsonview-sep d="M16 300 H824"/> <text class="nj-jsonview-mono nj-jsonview-xs" x=16 y=318 xml:space=preserve>view v = root()[&quot;tags&quot;] (taken after parse):</text> <text class="nj-jsonview-note nj-jsonview-c-struct nj-jsonview-strong" x=320 y=318 xml:space=preserve>valid, sees every edit</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=16 y=338 xml:space=preserve>iterator over tags (taken after parse):</text> <text class="nj-jsonview-note nj-jsonview-c-struct nj-jsonview-strong" x=320 y=338 xml:space=preserve>valid</text> <text class="nj-jsonview-mono nj-jsonview-xs nj-jsonview-muted" x=16 y=360 xml:space=preserve>dump(): {&quot;port&quot;:6379,&quot;price&quot;:19.90,&quot;tags&quot;:[&quot;eu&quot;,&quot;a\&quot;b&quot;]}</text> </svg> </div> <figcaption>Step 1 of 5. After parsing: nine nodes in the parsed index, no owned storage yet.</figcaption> </figure> <figure class=nj-jsonview-step data-label="set an existing member"> <div class=nj-jsonview-scroll> <svg class="nj-fig nj-jsonview nj-jsonview-editfig" viewbox="0 0 840 372" role=img aria-labelledby="fig-jve1-title fig-jve1-title-d" xmlns=http://www.w3.org/2000/svg> <title id=fig-jve1-title>Step 2 of 5: doc.set(doc.root(), &quot;port&quot;, 6380)</title> <desc id=fig-jve1-title-d>set: the node of the integer is overwritten in place. The dump with number_format::source is {&quot;port&quot;:6380,&quot;price&quot;:19.90,&quot;tags&quot;:[&quot;eu&quot;,&quot;a\&quot;b&quot;]}.</desc> <defs> <marker id=jve1-line viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-line nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve1-own viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-own nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve1-struct viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-struct nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve1-bad viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-bad nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> </defs> <text class="nj-jsonview-note nj-jsonview-strong" x=16 y=22 xml:space=preserve>parsed index: fixed, never moves</text> <text class=nj-jsonview-note x=824 y=22 text-anchor=end xml:space=preserve>the source text is never written</text> <rect x=36 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=42 y=47 xml:space=preserve>0</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=78 y=61 text-anchor=middle xml:space=preserve>object</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=78 y=77 text-anchor=middle xml:space=preserve>{ } 3</text> <rect x=124 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=130 y=47 xml:space=preserve>1</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=166 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=166 y=77 text-anchor=middle xml:space=preserve>port</text> <rect x=212 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=218 y=47 xml:space=preserve>2</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-num" x=254 y=61 text-anchor=middle xml:space=preserve>uint</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=254 y=77 text-anchor=middle xml:space=preserve>6380</text> <rect x=300 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=306 y=47 xml:space=preserve>3</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=342 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=342 y=77 text-anchor=middle xml:space=preserve>price</text> <rect x=388 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=394 y=47 xml:space=preserve>4</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-num" x=430 y=61 text-anchor=middle xml:space=preserve>float</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=430 y=77 text-anchor=middle xml:space=preserve>19.90</text> <rect x=476 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=482 y=47 xml:space=preserve>5</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=518 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=518 y=77 text-anchor=middle xml:space=preserve>tags</text> <rect x=564 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=570 y=47 xml:space=preserve>6</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=606 y=61 text-anchor=middle xml:space=preserve>array</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=606 y=77 text-anchor=middle xml:space=preserve>[ ] 2</text> <rect x=652 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-str"/> <text class=nj-jsonview-tiny x=658 y=47 xml:space=preserve>7</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-str" x=694 y=61 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=694 y=77 text-anchor=middle xml:space=preserve>&quot;eu&quot;</text> <rect x=740 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-dec"/> <text class=nj-jsonview-tiny x=746 y=47 xml:space=preserve>8</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-dec" x=782 y=61 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=782 y=77 text-anchor=middle xml:space=preserve>a&quot;b</text> <text class="nj-jsonview-note nj-jsonview-strong nj-jsonview-c-own" x=16 y=288 xml:space=preserve>owned storage: allocated on demand, never moves</text> <rect class=nj-jsonview-store x=10 y=192 width=820 height=54 rx=8 /> <text class=nj-jsonview-note x=26 y=224 xml:space=preserve>empty: a read-only json_document has none of this</text> <path class=nj-jsonview-sep d="M16 300 H824"/> <text class="nj-jsonview-mono nj-jsonview-xs" x=16 y=318 xml:space=preserve>view v = root()[&quot;tags&quot;] (taken after parse):</text> <text class="nj-jsonview-note nj-jsonview-c-struct nj-jsonview-strong" x=320 y=318 xml:space=preserve>valid, sees every edit</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=16 y=338 xml:space=preserve>iterator over tags (taken after parse):</text> <text class="nj-jsonview-note nj-jsonview-c-struct nj-jsonview-strong" x=320 y=338 xml:space=preserve>valid</text> <text class="nj-jsonview-mono nj-jsonview-xs nj-jsonview-muted" x=16 y=360 xml:space=preserve>dump(): {&quot;port&quot;:6380,&quot;price&quot;:19.90,&quot;tags&quot;:[&quot;eu&quot;,&quot;a\&quot;b&quot;]}</text> </svg> </div> <figcaption>Step 2 of 5. <code>doc.set(doc.root(), "port", 6380)</code> overwrites the node of the integer in place; no member is added or removed, so the object keeps its parsed layout.</figcaption> </figure> <figure class=nj-jsonview-step data-label="erase an array element"> <div class=nj-jsonview-scroll> <svg class="nj-fig nj-jsonview nj-jsonview-editfig" viewbox="0 0 840 372" role=img aria-labelledby="fig-jve2-title fig-jve2-title-d" xmlns=http://www.w3.org/2000/svg> <title id=fig-jve2-title>Step 3 of 5: doc.erase(doc.root()[&quot;tags&quot;], 0)</title> <desc id=fig-jve2-title-d>erase: the array moves to a block of links in owned storage. The dump with number_format::source is {&quot;port&quot;:6380,&quot;price&quot;:19.90,&quot;tags&quot;:[&quot;a\&quot;b&quot;]}.</desc> <defs> <marker id=jve2-line viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-line nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve2-own viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-own nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve2-struct viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-struct nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve2-bad viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-bad nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> </defs> <text class="nj-jsonview-note nj-jsonview-strong" x=16 y=22 xml:space=preserve>parsed index: fixed, never moves</text> <text class=nj-jsonview-note x=824 y=22 text-anchor=end xml:space=preserve>the source text is never written</text> <rect x=36 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=42 y=47 xml:space=preserve>0</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=78 y=61 text-anchor=middle xml:space=preserve>object</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=78 y=77 text-anchor=middle xml:space=preserve>{ } 3</text> <rect x=124 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=130 y=47 xml:space=preserve>1</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=166 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=166 y=77 text-anchor=middle xml:space=preserve>port</text> <rect x=212 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=218 y=47 xml:space=preserve>2</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-num" x=254 y=61 text-anchor=middle xml:space=preserve>uint</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=254 y=77 text-anchor=middle xml:space=preserve>6380</text> <rect x=300 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=306 y=47 xml:space=preserve>3</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=342 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=342 y=77 text-anchor=middle xml:space=preserve>price</text> <rect x=388 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=394 y=47 xml:space=preserve>4</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-num" x=430 y=61 text-anchor=middle xml:space=preserve>float</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=430 y=77 text-anchor=middle xml:space=preserve>19.90</text> <rect x=476 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=482 y=47 xml:space=preserve>5</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=518 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=518 y=77 text-anchor=middle xml:space=preserve>tags</text> <rect x=564 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=570 y=47 xml:space=preserve>6</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=606 y=61 text-anchor=middle xml:space=preserve>array</text> <text class="nj-jsonview-tiny nj-jsonview-c-struct nj-jsonview-strong" x=643 y=47 text-anchor=end xml:space=preserve>moved</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=606 y=77 text-anchor=middle xml:space=preserve>[ ] 2</text> <rect x=652 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-gap nj-jsonview-c-str"/> <text class=nj-jsonview-tiny x=658 y=47 xml:space=preserve>7</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-str" x=694 y=61 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=694 y=77 text-anchor=middle xml:space=preserve>&quot;eu&quot;</text> <text class="nj-jsonview-tiny nj-jsonview-c-bad" x=694 y=98 text-anchor=middle xml:space=preserve>unreferenced</text> <rect x=740 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-dec"/> <text class=nj-jsonview-tiny x=746 y=47 xml:space=preserve>8</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-dec" x=782 y=61 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=782 y=77 text-anchor=middle xml:space=preserve>a&quot;b</text> <text class="nj-jsonview-note nj-jsonview-strong nj-jsonview-c-own" x=16 y=288 xml:space=preserve>owned storage: allocated on demand, never moves</text> <rect class=nj-jsonview-store x=10 y=192 width=820 height=54 rx=8 /> <rect x=16 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=66 y=207 text-anchor=end xml:space=preserve>0&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=43 y=220 text-anchor=middle xml:space=preserve>header</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=43 y=235 text-anchor=middle xml:space=preserve>[ ] 1</text> <rect x=73 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-own"/> <text class=nj-jsonview-tiny x=123 y=207 text-anchor=end xml:space=preserve>1&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-own" x=100 y=220 text-anchor=middle xml:space=preserve>link</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=100 y=235 text-anchor=middle xml:space=preserve>→ 8</text> <path class="nj-jsonview-arr nj-jsonview-c-own" marker-end=url(#jve2-own) d="M100 196 C100 140 782 140 782 84"/> <rect x=130 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-free nj-jsonview-c-own"/> <text class=nj-jsonview-tiny x=157 y=224 text-anchor=middle xml:space=preserve>free</text> <path class="nj-jsonview-arr nj-jsonview-c-struct nj-jsonview-dash" marker-end=url(#jve2-struct) d="M598 84 C598 140 43 140 43 196"/> <path class=nj-jsonview-sep d="M16 300 H824"/> <text class="nj-jsonview-mono nj-jsonview-xs" x=16 y=318 xml:space=preserve>view v = root()[&quot;tags&quot;] (taken after parse):</text> <text class="nj-jsonview-note nj-jsonview-c-struct nj-jsonview-strong" x=320 y=318 xml:space=preserve>valid, sees every edit</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=16 y=338 xml:space=preserve>iterator over tags (taken after parse):</text> <text class="nj-jsonview-note nj-jsonview-c-bad nj-jsonview-strong" x=320 y=338 xml:space=preserve>invalid: tags no longer uses the parsed layout</text> <text class="nj-jsonview-mono nj-jsonview-xs nj-jsonview-muted" x=16 y=360 xml:space=preserve>dump(): {&quot;port&quot;:6380,&quot;price&quot;:19.90,&quot;tags&quot;:[&quot;a\&quot;b&quot;]}</text> </svg> </div> <figcaption>Step 3 of 5. <code>doc.erase(doc.root()["tags"], 0)</code>: the array is edited for the first time, so its elements move to a block of links in owned storage. The node of <code>"eu"</code> stays in the index, but nothing refers to it any more; iterators over the array taken before are invalid.</figcaption> </figure> <figure class=nj-jsonview-step data-label="push_back onto the array"> <div class=nj-jsonview-scroll> <svg class="nj-fig nj-jsonview nj-jsonview-editfig" viewbox="0 0 840 372" role=img aria-labelledby="fig-jve3-title fig-jve3-title-d" xmlns=http://www.w3.org/2000/svg> <title id=fig-jve3-title>Step 4 of 5: doc.push_back(doc.root()[&quot;tags&quot;], &quot;new&quot;)</title> <desc id=fig-jve3-title-d>push_back: a new node, and a link appended to the block. The dump with number_format::source is {&quot;port&quot;:6380,&quot;price&quot;:19.90,&quot;tags&quot;:[&quot;a\&quot;b&quot;,&quot;new&quot;]}.</desc> <defs> <marker id=jve3-line viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-line nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve3-own viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-own nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve3-struct viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-struct nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve3-bad viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-bad nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> </defs> <text class="nj-jsonview-note nj-jsonview-strong" x=16 y=22 xml:space=preserve>parsed index: fixed, never moves</text> <text class=nj-jsonview-note x=824 y=22 text-anchor=end xml:space=preserve>the source text is never written</text> <rect x=36 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=42 y=47 xml:space=preserve>0</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=78 y=61 text-anchor=middle xml:space=preserve>object</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=78 y=77 text-anchor=middle xml:space=preserve>{ } 3</text> <rect x=124 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=130 y=47 xml:space=preserve>1</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=166 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=166 y=77 text-anchor=middle xml:space=preserve>port</text> <rect x=212 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=218 y=47 xml:space=preserve>2</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-num" x=254 y=61 text-anchor=middle xml:space=preserve>uint</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=254 y=77 text-anchor=middle xml:space=preserve>6380</text> <rect x=300 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=306 y=47 xml:space=preserve>3</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=342 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=342 y=77 text-anchor=middle xml:space=preserve>price</text> <rect x=388 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=394 y=47 xml:space=preserve>4</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-num" x=430 y=61 text-anchor=middle xml:space=preserve>float</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=430 y=77 text-anchor=middle xml:space=preserve>19.90</text> <rect x=476 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=482 y=47 xml:space=preserve>5</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=518 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=518 y=77 text-anchor=middle xml:space=preserve>tags</text> <rect x=564 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=570 y=47 xml:space=preserve>6</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=606 y=61 text-anchor=middle xml:space=preserve>array</text> <text class="nj-jsonview-tiny nj-jsonview-c-struct nj-jsonview-strong" x=643 y=47 text-anchor=end xml:space=preserve>moved</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=606 y=77 text-anchor=middle xml:space=preserve>[ ] 2</text> <rect x=652 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-gap nj-jsonview-c-str"/> <text class=nj-jsonview-tiny x=658 y=47 xml:space=preserve>7</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-str" x=694 y=61 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=694 y=77 text-anchor=middle xml:space=preserve>&quot;eu&quot;</text> <text class="nj-jsonview-tiny nj-jsonview-c-bad" x=694 y=98 text-anchor=middle xml:space=preserve>unreferenced</text> <rect x=740 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-dec"/> <text class=nj-jsonview-tiny x=746 y=47 xml:space=preserve>8</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-dec" x=782 y=61 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=782 y=77 text-anchor=middle xml:space=preserve>a&quot;b</text> <text class="nj-jsonview-note nj-jsonview-strong nj-jsonview-c-own" x=16 y=288 xml:space=preserve>owned storage: allocated on demand, never moves</text> <rect class=nj-jsonview-store x=10 y=192 width=820 height=54 rx=8 /> <rect x=16 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=66 y=207 text-anchor=end xml:space=preserve>0&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=43 y=220 text-anchor=middle xml:space=preserve>header</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=43 y=235 text-anchor=middle xml:space=preserve>[ ] 2</text> <rect x=73 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-c-own"/> <text class=nj-jsonview-tiny x=123 y=207 text-anchor=end xml:space=preserve>1&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-own" x=100 y=220 text-anchor=middle xml:space=preserve>link</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=100 y=235 text-anchor=middle xml:space=preserve>→ 8</text> <path class="nj-jsonview-arr nj-jsonview-c-own" marker-end=url(#jve3-own) d="M100 196 C100 140 782 140 782 84"/> <rect x=130 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-own"/> <text class=nj-jsonview-tiny x=180 y=207 text-anchor=end xml:space=preserve>2&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-own" x=157 y=220 text-anchor=middle xml:space=preserve>link</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=157 y=235 text-anchor=middle xml:space=preserve>→ 3&#x27;</text> <path class="nj-jsonview-arr nj-jsonview-c-own" marker-end=url(#jve3-own) d="M157 242 C157 268 214 268 214 244"/> <rect x=187 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-str"/> <text class=nj-jsonview-tiny x=237 y=207 text-anchor=end xml:space=preserve>3&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-str" x=214 y=220 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=214 y=235 text-anchor=middle xml:space=preserve>&quot;new&quot;</text> <path class="nj-jsonview-arr nj-jsonview-c-struct nj-jsonview-dash" marker-end=url(#jve3-struct) d="M598 84 C598 140 43 140 43 196"/> <text class=nj-jsonview-note x=588 y=282 text-anchor=end xml:space=preserve>edited text</text> <rect x=596 y=264 width=42 height=26 rx=4 class="nj-jsonview-node nj-jsonview-c-str"/> <text class="nj-jsonview-mono nj-jsonview-sm" x=602 y=282 xml:space=preserve>new</text> <path class=nj-jsonview-sep d="M16 300 H824"/> <text class="nj-jsonview-mono nj-jsonview-xs" x=16 y=318 xml:space=preserve>view v = root()[&quot;tags&quot;] (taken after parse):</text> <text class="nj-jsonview-note nj-jsonview-c-struct nj-jsonview-strong" x=320 y=318 xml:space=preserve>valid, sees every edit</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=16 y=338 xml:space=preserve>iterator over tags (taken after parse):</text> <text class="nj-jsonview-note nj-jsonview-c-bad nj-jsonview-strong" x=320 y=338 xml:space=preserve>invalid: tags no longer uses the parsed layout</text> <text class="nj-jsonview-mono nj-jsonview-xs nj-jsonview-muted" x=16 y=360 xml:space=preserve>dump(): {&quot;port&quot;:6380,&quot;price&quot;:19.90,&quot;tags&quot;:[&quot;a\&quot;b&quot;,&quot;new&quot;]}</text> </svg> </div> <figcaption>Step 4 of 5. <code>doc.push_back(doc.root()["tags"], "new")</code>: the new string gets its own node, its text goes to the buffer of edited text, and a link to it is appended to the block of the array.</figcaption> </figure> <figure class=nj-jsonview-step data-label="set a new member"> <div class=nj-jsonview-scroll> <svg class="nj-fig nj-jsonview nj-jsonview-editfig" viewbox="0 0 840 372" role=img aria-labelledby="fig-jve4-title fig-jve4-title-d" xmlns=http://www.w3.org/2000/svg> <title id=fig-jve4-title>Step 5 of 5: doc.set(doc.root(), &quot;retries&quot;, 3)</title> <desc id=fig-jve4-title-d>set of a new member: the object moves to a block as well. The dump with number_format::source is {&quot;port&quot;:6380,&quot;price&quot;:19.90,&quot;tags&quot;:[&quot;a\&quot;b&quot;,&quot;new&quot;],&quot;retries&quot;:3}.</desc> <defs> <marker id=jve4-line viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-line nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve4-own viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-own nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve4-struct viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-struct nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> <marker id=jve4-bad viewbox="0 0 10 10" refx=9 refy=5 markerwidth=6.5 markerheight=6.5 orient=auto-start-reverse><path class="nj-jsonview-c-bad nj-jsonview-head" d="M0 1 L10 5 L0 9 z"/></marker> </defs> <text class="nj-jsonview-note nj-jsonview-strong" x=16 y=22 xml:space=preserve>parsed index: fixed, never moves</text> <text class=nj-jsonview-note x=824 y=22 text-anchor=end xml:space=preserve>the source text is never written</text> <rect x=36 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=42 y=47 xml:space=preserve>0</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=78 y=61 text-anchor=middle xml:space=preserve>object</text> <text class="nj-jsonview-tiny nj-jsonview-c-struct nj-jsonview-strong" x=115 y=47 text-anchor=end xml:space=preserve>moved</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=78 y=77 text-anchor=middle xml:space=preserve>{ } 3</text> <rect x=124 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=130 y=47 xml:space=preserve>1</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=166 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=166 y=77 text-anchor=middle xml:space=preserve>port</text> <rect x=212 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=218 y=47 xml:space=preserve>2</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-num" x=254 y=61 text-anchor=middle xml:space=preserve>uint</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=254 y=77 text-anchor=middle xml:space=preserve>6380</text> <rect x=300 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=306 y=47 xml:space=preserve>3</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=342 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=342 y=77 text-anchor=middle xml:space=preserve>price</text> <rect x=388 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=394 y=47 xml:space=preserve>4</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-num" x=430 y=61 text-anchor=middle xml:space=preserve>float</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=430 y=77 text-anchor=middle xml:space=preserve>19.90</text> <rect x=476 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=482 y=47 xml:space=preserve>5</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=518 y=61 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=518 y=77 text-anchor=middle xml:space=preserve>tags</text> <rect x=564 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=570 y=47 xml:space=preserve>6</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=606 y=61 text-anchor=middle xml:space=preserve>array</text> <text class="nj-jsonview-tiny nj-jsonview-c-struct nj-jsonview-strong" x=643 y=47 text-anchor=end xml:space=preserve>moved</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=606 y=77 text-anchor=middle xml:space=preserve>[ ] 2</text> <rect x=652 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-gap nj-jsonview-c-str"/> <text class=nj-jsonview-tiny x=658 y=47 xml:space=preserve>7</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-str" x=694 y=61 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=694 y=77 text-anchor=middle xml:space=preserve>&quot;eu&quot;</text> <text class="nj-jsonview-tiny nj-jsonview-c-bad" x=694 y=98 text-anchor=middle xml:space=preserve>unreferenced</text> <rect x=740 y=34 width=84 height=50 rx=5 class="nj-jsonview-node nj-jsonview-c-dec"/> <text class=nj-jsonview-tiny x=746 y=47 xml:space=preserve>8</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-dec" x=782 y=61 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-sm" x=782 y=77 text-anchor=middle xml:space=preserve>a&quot;b</text> <text class="nj-jsonview-note nj-jsonview-strong nj-jsonview-c-own" x=16 y=288 xml:space=preserve>owned storage: allocated on demand, never moves</text> <rect class=nj-jsonview-store x=10 y=192 width=820 height=54 rx=8 /> <rect x=16 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=66 y=207 text-anchor=end xml:space=preserve>0&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=43 y=220 text-anchor=middle xml:space=preserve>header</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=43 y=235 text-anchor=middle xml:space=preserve>[ ] 2</text> <rect x=73 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-c-own"/> <text class=nj-jsonview-tiny x=123 y=207 text-anchor=end xml:space=preserve>1&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-own" x=100 y=220 text-anchor=middle xml:space=preserve>link</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=100 y=235 text-anchor=middle xml:space=preserve>→ 8</text> <path class="nj-jsonview-arr nj-jsonview-c-own" marker-end=url(#jve4-own) d="M100 196 C100 140 782 140 782 84"/> <rect x=130 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-c-own"/> <text class=nj-jsonview-tiny x=180 y=207 text-anchor=end xml:space=preserve>2&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-own" x=157 y=220 text-anchor=middle xml:space=preserve>link</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=157 y=235 text-anchor=middle xml:space=preserve>→ 3&#x27;</text> <path class="nj-jsonview-arr nj-jsonview-c-own" marker-end=url(#jve4-own) d="M157 242 C157 268 214 268 214 244"/> <rect x=187 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-c-str"/> <text class=nj-jsonview-tiny x=237 y=207 text-anchor=end xml:space=preserve>3&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-str" x=214 y=220 text-anchor=middle xml:space=preserve>string</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=214 y=235 text-anchor=middle xml:space=preserve>&quot;new&quot;</text> <rect x=244 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-num"/> <text class=nj-jsonview-tiny x=294 y=207 text-anchor=end xml:space=preserve>4&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-num" x=271 y=220 text-anchor=middle xml:space=preserve>uint</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=271 y=235 text-anchor=middle xml:space=preserve>3</text> <rect x=301 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-struct"/> <text class=nj-jsonview-tiny x=351 y=207 text-anchor=end xml:space=preserve>5&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-struct" x=328 y=220 text-anchor=middle xml:space=preserve>header</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=328 y=235 text-anchor=middle xml:space=preserve>{ } 4</text> <rect x=358 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=408 y=207 text-anchor=end xml:space=preserve>6&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=385 y=220 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=385 y=235 text-anchor=middle xml:space=preserve>port</text> <rect x=415 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-own"/> <text class=nj-jsonview-tiny x=465 y=207 text-anchor=end xml:space=preserve>7&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-own" x=442 y=220 text-anchor=middle xml:space=preserve>link</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=442 y=235 text-anchor=middle xml:space=preserve>→ 2</text> <path class="nj-jsonview-arr nj-jsonview-c-own" marker-end=url(#jve4-own) d="M442 196 C442 140 254 140 254 84"/> <rect x=472 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=522 y=207 text-anchor=end xml:space=preserve>8&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=499 y=220 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=499 y=235 text-anchor=middle xml:space=preserve>price</text> <rect x=529 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-own"/> <text class=nj-jsonview-tiny x=579 y=207 text-anchor=end xml:space=preserve>9&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-own" x=556 y=220 text-anchor=middle xml:space=preserve>link</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=556 y=235 text-anchor=middle xml:space=preserve>→ 4</text> <path class="nj-jsonview-arr nj-jsonview-c-own" marker-end=url(#jve4-own) d="M556 196 C556 140 430 140 430 84"/> <rect x=586 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=636 y=207 text-anchor=end xml:space=preserve>10&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=613 y=220 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=613 y=235 text-anchor=middle xml:space=preserve>tags</text> <rect x=643 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-own"/> <text class=nj-jsonview-tiny x=693 y=207 text-anchor=end xml:space=preserve>11&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-own" x=670 y=220 text-anchor=middle xml:space=preserve>link</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=670 y=235 text-anchor=middle xml:space=preserve>→ 6</text> <path class="nj-jsonview-arr nj-jsonview-c-own" marker-end=url(#jve4-own) d="M670 196 C670 140 614 140 614 84"/> <rect x=700 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-key"/> <text class=nj-jsonview-tiny x=750 y=207 text-anchor=end xml:space=preserve>12&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-key" x=727 y=220 text-anchor=middle xml:space=preserve>key</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=727 y=235 text-anchor=middle xml:space=preserve>retries</text> <rect x=757 y=196 width=54 height=46 rx=5 class="nj-jsonview-node nj-jsonview-hot nj-jsonview-c-own"/> <text class=nj-jsonview-tiny x=807 y=207 text-anchor=end xml:space=preserve>13&#x27;</text> <text class="nj-jsonview-kind nj-jsonview-xs nj-jsonview-c-own" x=784 y=220 text-anchor=middle xml:space=preserve>link</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=784 y=235 text-anchor=middle xml:space=preserve>→ 4&#x27;</text> <path class="nj-jsonview-arr nj-jsonview-c-own" marker-end=url(#jve4-own) d="M784 242 C784 268 271 268 271 244"/> <path class="nj-jsonview-arr nj-jsonview-c-struct nj-jsonview-dash" marker-end=url(#jve4-struct) d="M598 84 C598 140 43 140 43 196"/> <path class="nj-jsonview-arr nj-jsonview-c-struct nj-jsonview-dash" marker-end=url(#jve4-struct) d="M70 84 C70 140 328 140 328 196"/> <text class=nj-jsonview-note x=588 y=282 text-anchor=end xml:space=preserve>edited text</text> <rect x=596 y=264 width=112 height=26 rx=4 class="nj-jsonview-node nj-jsonview-c-str"/> <text class="nj-jsonview-mono nj-jsonview-sm" x=602 y=282 xml:space=preserve>newretries</text> <path class=nj-jsonview-sep d="M16 300 H824"/> <text class="nj-jsonview-mono nj-jsonview-xs" x=16 y=318 xml:space=preserve>view v = root()[&quot;tags&quot;] (taken after parse):</text> <text class="nj-jsonview-note nj-jsonview-c-struct nj-jsonview-strong" x=320 y=318 xml:space=preserve>valid, sees every edit</text> <text class="nj-jsonview-mono nj-jsonview-xs" x=16 y=338 xml:space=preserve>iterator over tags (taken after parse):</text> <text class="nj-jsonview-note nj-jsonview-c-bad nj-jsonview-strong" x=320 y=338 xml:space=preserve>invalid: tags no longer uses the parsed layout</text> <text class="nj-jsonview-mono nj-jsonview-xs nj-jsonview-muted" x=16 y=360 xml:space=preserve>dump(): {&quot;port&quot;:6380,&quot;price&quot;:19.90,&quot;tags&quot;:[&quot;a\&quot;b&quot;,&quot;new&quot;],&quot;retries&quot;:3}</text> </svg> </div> <figcaption>Step 5 of 5. <code>doc.set(doc.root(), "retries", 3)</code>: a new member, so the object moves to a block too: copies of its keys, links to the values it already had, then the new key and a link to the new integer.</figcaption> </figure> </div> <p class=nj-caption>The node index and the owned storage of the document after each of five edits. Use <em>Back</em>, <em>Next</em>, or the numbered buttons to switch between the steps; without JavaScript all steps are shown one below the other.</p> <h2 id=images>Images<a class=headerlink href=#images title="Permanent link">&para;</a></h2> <p><a href=../../api/basic_json_document/save/ ><code>save()</code></a> writes a document as an <em>image</em>: a byte buffer that <a href=../../api/basic_json_document/load/ ><code>load()</code></a> reads back into a document without parsing — no lexing, no building the node index, nothing but copying the nodes and pointing the text and the decoded strings at the image. Where <a href=../../api/basic_json_document/parse_copy/ ><code>parse_copy()</code></a> still has to scan the whole input, <a href=../../api/basic_json_document/load/ ><code>load()</code></a> turns that scan into a copy of the node index alone.</p> <p><strong>Why.</strong> A document that is parsed once and then read many times — a configuration loaded at startup, a template rendered on every request, a large reference dataset a worker process needs in memory — pays for parsing once but can amortize <a href=../../api/basic_json_document/save/ ><code>save()</code></a>'s cost across every later load. That makes images useful for a cache: save a document the first time it is parsed (to a file, a shared-memory segment, an in-process cache), and <a href=../../api/basic_json_document/load/ ><code>load()</code></a> it on every later use instead of parsing the source text again. They are just as useful for handing a parsed document to another process (or a forked worker) running the same build of the library, since <a href=../../api/basic_json_document/load/ ><code>load()</code></a> turns the transfer into a copy of the node index plus pointers into the received bytes, not a re-parse.</p> <p><strong>Choosing a check.</strong> <a href=../../api/basic_json_document/load/ ><code>load()</code></a> takes an <a href=../../api/basic_json_document/load/#image_check><code>image_check</code></a> that trades validation against speed: <code>image_check::full</code> (the default) checks everything the parser itself guarantees, so a checked image is exactly as safe to read and serialize as a freshly parsed document — the right choice whenever the image did not come straight from this process's own <a href=../../api/basic_json_document/save/ ><code>save()</code></a>, such as a file or a network peer. <code>image_check::bounds</code> only checks structure and bounds — cheaper, since it skips scanning the text and the decoded strings — and fits a cache the process trusts, one it wrote and reads back itself. <code>image_check::none</code> skips validation entirely, for an image trusted as much as the process's own memory. See <a href=../../api/basic_json_document/load/#notes><code>load()</code>'s Notes</a> for exactly what each level does and does not guarantee.</p> <details class=example> <summary>Example: cache a parsed configuration as an image</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;cstdint&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;string&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;vector&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json_document</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=p>;</span>
<span class=w> </span><span class=c1>// a configuration a service parses once and then caches as an image, so</span>
<span class=w> </span><span class=c1>// that later requests can load() it instead of parsing the text again</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=w> </span><span class=n>text</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span><span class=s>{"name": "cache", "host": "db1", "port": 6379, "replicas": ["db2", "db3"]}</span><span class=dl>)</span><span class=s>"</span><span class=p>;</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>json_document</span><span class=w> </span><span class=n>config</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json_document</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>text</span><span class=p>);</span>
<span class=w> </span><span class=c1>// save() turns the parsed document into a byte buffer: a 64-byte header,</span>
<span class=w> </span><span class=c1>// the node index, the source text, and the decoded strings</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span><span class=w> </span><span class=n>image</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>config</span><span class=p>.</span><span class=n>save</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>image</span><span class=p>.</span><span class=n>size</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// the same document always saves to the same bytes</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=p>(</span><span class=n>image</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>json_document</span><span class=o>::</span><span class=n>parse</span><span class=p>(</span><span class=n>text</span><span class=p>).</span><span class=n>save</span><span class=p>())</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// loading the image back needs no parsing, yet dumps exactly what</span>
<span class=w> </span><span class=c1>// parsing the text produced</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>json_document</span><span class=w> </span><span class=n>reloaded</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json_document</span><span class=o>::</span><span class=n>load</span><span class=p>(</span><span class=n>image</span><span class=p>);</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=p>(</span><span class=n>reloaded</span><span class=p>.</span><span class=n>root</span><span class=p>().</span><span class=n>dump</span><span class=p>()</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>config</span><span class=p>.</span><span class=n>root</span><span class=p>().</span><span class=n>dump</span><span class=p>())</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=mi>316</span>
<span class=kc>true</span>
<span class=kc>true</span>
</code></pre></div> </details> <div class="admonition warning"> <p class=admonition-title>Experimental</p> <p>The image format is versioned but not yet stable, and may change in an incompatible way before it is declared stable. It is little-endian only (on big-endian targets, <code>save()</code> and <code>load()</code> do not exist), and tied to the library build that wrote it — use it to cache a document or to hand one to another process running the <em>same</em> build, not as a long-term storage format; keep the original <abbr title="JavaScript Object Notation">JSON</abbr> text if a saved document needs to be readable by a future library version.</p> </div> <p>The idea of a document you can read without parsing comes from zero-copy formats such as <a href="https://github.com/google/flatbuffers">FlatBuffers</a> and <a href="https://github.com/yandex/yaff">YaFF</a>; the check <a href=../../api/basic_json_document/load/ ><code>load()</code></a> runs follows the idea of FlatBuffers' Verifier. No code is taken from either.</p> <h2 id=choosing-between-json-ordered_json-the-sax-interface-and-json_view>Choosing between <code>json</code>, <code>ordered_json</code>, the <abbr title="Simple API for XML">SAX</abbr> interface, and <code>json_view</code><a class=headerlink href=#choosing-between-json-ordered_json-the-sax-interface-and-json_view title="Permanent link">&para;</a></h2> <table> <thead> <tr> <th></th> <th><a href=../../api/json/ ><code>json</code></a> / <a href=../../api/ordered_json/ ><code>ordered_json</code></a></th> <th><a href=../parsing/sax_interface/ ><abbr title="Simple API for XML">SAX</abbr> interface</a></th> <th><a href=../../api/json_document/ ><code>json_document</code></a> / <a href=../../api/json_view/ ><code>json_view</code></a></th> <th><a href=../../api/json_editable_document/ ><code>json_editable_document</code></a> / <a href=../../api/json_editable_view/ ><code>json_editable_view</code></a></th> </tr> </thead> <tbody> <tr> <td><strong>Ownership</strong></td> <td>owns every value</td> <td>owns nothing; you decide what to keep, in your handler</td> <td>borrows or owns the <em>text</em>; the index is always owned by the document</td> <td>same as <code>json_document</code>; edits go to storage the document owns</td> </tr> <tr> <td><strong>Mutability</strong></td> <td>freely mutable</td> <td>not applicable (a one-shot event stream)</td> <td>read-only</td> <td><a href=../../api/basic_json_document/set/ ><code>set</code></a>/<a href=../../api/basic_json_document/push_back/ ><code>push_back</code></a>/<a href=../../api/basic_json_document/insert/ ><code>insert</code></a>/<a href=../../api/basic_json_document/erase/ ><code>erase</code></a> edit in place; the source text is never rewritten</td> </tr> <tr> <td><strong>What you get</strong></td> <td>a full tree you can read, write, and keep as long as you like</td> <td>a sequence of callbacks; whatever your handler builds from them</td> <td>a flat index plus, on demand, <a href=../../api/basic_json_view/materialize/ ><code>materialize()</code></a>d <code>json</code>/<code>ordered_json</code> values for the parts you actually use</td> <td>the same, plus <a href=../../api/basic_json_view/dump/ ><code>dump()</code></a> of an edited document that keeps the member order and, with <a href=../../api/basic_json_view/number_format/ ><code>number_format::source</code></a>, the spelling of every untouched number</td> </tr> <tr> <td><strong>Typical use</strong></td> <td>general-purpose <abbr title="JavaScript Object Notation">JSON</abbr> handling: config, request/response bodies you build or modify, anything you hold onto</td> <td>validating or projecting a text into your own data structure without ever holding the whole thing as <abbr title="JavaScript Object Notation">JSON</abbr></td> <td>large or high-volume input where you only need part of it, or need it repeatedly, and can keep the source text (or a copy) alive for as long as the document lives</td> <td>a document you read, patch a few fields of, and write back — a configuration file, for instance — where the rest of it should come back exactly as it was</td> </tr> <tr> <td><strong>Caching/reload</strong></td> <td>not applicable — re-parse, or roll your own serialization</td> <td>not applicable</td> <td><a href=../../api/basic_json_document/save/ ><code>save()</code></a>/<a href=../../api/basic_json_document/load/ ><code>load()</code></a>: cache the parsed index as an image and reload it without parsing</td> <td>same, saving the document's current — possibly edited — state</td> </tr> </tbody> </table> <p class=nj-table-caption>Each column is one way to work with <abbr title="JavaScript Object Notation">JSON</abbr> in this library, and each row compares one property of them.</p> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../api/basic_json_document/ ><code>basic_json_document</code></a> - the document that owns the parsed index (parse, access, images, edits)</li> <li><a href=../../api/basic_json_view/ ><code>basic_json_view</code></a> - the non-owning handle to a value in a document</li> <li><a href=../../api/json_document/ ><code>json_document</code></a> - and <a href=../../api/ordered_json_document/ ><code>ordered_json_document</code></a> - the read-only documents</li> <li><a href=../../api/json_editable_document/ ><code>json_editable_document</code></a> - and <a href=../../api/ordered_json_editable_document/ ><code>ordered_json_editable_document</code></a> - the documents that can be edited in place</li> <li><a href=../../home/architecture/#node-index-of-json-views>Architecture</a> - the layout of the node index</li> <li><a href=../parsing/sax_interface/ ><abbr title="Simple API for XML">SAX</abbr> interface</a> - event-based parsing without building a tree</li> <li><a href=../performance/ >Performance</a> - benchmarks and tuning of parsing and serialization</li> <li><a href=../parsing/large_and_partial_input/ >Large, Streamed, and Partial Input</a> - 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