json/api/json_editable_view/index.md

nlohmann::json_editable_view

Defined in header <nlohmann/json_view.hpp>

using json_editable_view = basic_json_view<json, view_mode::editable>;

This type is a basic_json_view of a value of a json_editable_document. It offers the same read-only interface as json_view; what is different is what it can be a view of — a value that set and push_back can change, with every view still referring to it seeing the change, see Edits.

Examples

Example

The example below is the same as json_editable_document's: every view read back out of the document — doc.root() and the views nested under it — sees the edits made through set.

#include <iostream>
#include <nlohmann/json_view.hpp>

using nlohmann::json;
using nlohmann::json_editable_document;
using nlohmann::json_editable_view;

int main()
{
    // a configuration file, as it might be read from disk
    const std::string text = R"({"name": "cache", "host": "db1", "port": 6379, "price": 19.90})";
    std::cout << text << "\n\n";

    // patch two fields -- "price" is never touched
    json_editable_document doc = json_editable_document::parse(text);
    doc.set(doc.root(), "host", "db2");
    doc.set(doc.root(), "retries", 3);

    // member order (the new member at the end) and the untouched number's
    // exact spelling survive
    std::cout << doc.root().dump(-1, ' ', false, json_editable_view::number_format::source) << '\n';

    // the same patch on a plain json value: keys are sorted (object_t is a
    // std::map), and "price" is rewritten even though the patch never
    // touched it
    json plain = json::parse(text);
    plain["host"] = "db2";
    plain["retries"] = 3;
    std::cout << plain.dump() << '\n';
}

Output:

{"name": "cache", "host": "db1", "port": 6379, "price": 19.90}

{"name":"cache","host":"db2","port":6379,"price":19.90,"retries":3}
{"host":"db2","name":"cache","port":6379,"price":19.9,"retries":3}

See also

• json_editable_document - the document type this view refers into
• json_view - the corresponding read-only view
• ordered_json_editable_view - the corresponding view for ordered_json_editable_document
• Zero-copy JSON views - editing a document in place and writing it back

Version history

Added in version 3.13.0 unreleased.