78 lines
2.8 KiB
Markdown
78 lines
2.8 KiB
Markdown
# <small>nlohmann::</small>json_editable_document
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<small>Defined in header `<nlohmann/json_view.hpp>`</small>
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```cpp
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using json_editable_document = basic_json_document<json, true>;
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```
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This type is an **editable** [`basic_json_document`](basic_json_document/index.md) of the default
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[`json`](json.md) specialization: in addition to everything [`json_document`](json_document.md) offers,
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[`set`](basic_json_document/set.md) and [`push_back`](basic_json_document/push_back.md) change values after
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parsing, without ever rewriting the source text -- see [Edits](basic_json_document/index.md#edits) and
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[Editing a document](../features/json_view.md#editing-a-document).
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## Examples
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??? example
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The example below patches two fields of a small configuration document -- changing one and adding another --
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and dumps it back out with the member order and the spelling of the untouched number preserved, something a
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plain [`json`](json.md) value cannot do.
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```cpp
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#include <iostream>
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#include <nlohmann/json_view.hpp>
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using json = nlohmann::json;
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using json_editable_document = nlohmann::json_editable_document;
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using json_editable_view = nlohmann::json_editable_view;
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int main()
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{
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// a configuration file, as it might be read from disk
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const std::string text = R"({"name": "cache", "host": "db1", "port": 6379, "price": 19.90})";
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std::cout << text << "\n\n";
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// patch two fields -- "price" is never touched
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json_editable_document doc = json_editable_document::parse(text);
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doc.set(doc.root(), "host", "db2");
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doc.set(doc.root(), "retries", 3);
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// member order (the new member at the end) and the untouched number's
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// exact spelling survive
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std::cout << doc.root().dump(-1, ' ', false, json_editable_view::number_format::source) << '\n';
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// the same patch on a plain json value: keys are sorted (object_t is a
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// std::map), and "price" is rewritten even though the patch never
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// touched it
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json plain = json::parse(text);
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plain["host"] = "db2";
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plain["retries"] = 3;
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std::cout << plain.dump() << '\n';
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}
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```
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Output:
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```json
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{"name": "cache", "host": "db1", "port": 6379, "price": 19.90}
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{"name":"cache","host":"db2","port":6379,"price":19.90,"retries":3}
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{"host":"db2","name":"cache","port":6379,"price":19.9,"retries":3}
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```
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## See also
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- [json_editable_view](json_editable_view.md) - a view of a value of a `json_editable_document`
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- [json_document](json_document.md) - the read-only document this type adds edits to
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- [ordered_json_editable_document](ordered_json_editable_document.md) - the corresponding editable document for
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`ordered_json`
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- [Edits](basic_json_document/index.md#edits) - what an edit guarantees
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## Version history
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Since version 3.13.0.
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