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nlohmann
80 lines
1.9 KiB
Markdown
80 lines
1.9 KiB
Markdown
# nlohmann::operator""\_json
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```
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json operator ""_json(const char* s, std::size_t n);
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json operator ""_json(const char8_t* s, std::size_t n); // since C++20
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```
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This operator implements a user-defined string literal for JSON objects. It can be used by adding `_json` to a string literal and returns a [`json`](https://json.nlohmann.me/api/json/index.md) object if no parse error occurred.
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It is recommended to bring the operator into scope using any of the following lines:
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```
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using nlohmann::literals::operator ""_json;
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using namespace nlohmann::literals;
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using namespace nlohmann::json_literals;
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using namespace nlohmann::literals::json_literals;
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using namespace nlohmann;
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```
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This is suggested to ease migration to the next major version release of the library. See [`JSON_USE_GLOBAL_UDLS`](https://json.nlohmann.me/api/macros/json_use_global_udls/#notes) for details.
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## Parameters
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`s` (in) : a string representation of a JSON object
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`n` (in) : length of string `s`
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## Return value
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[`json`](https://json.nlohmann.me/api/json/index.md) value parsed from `s`
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## Exceptions
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The function can throw anything that [`parse(s, s+n)`](https://json.nlohmann.me/api/basic_json/parse/index.md) would throw.
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## Complexity
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Linear.
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## Examples
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Example
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The following code shows how to create JSON values from string literals.
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```
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#include <iostream>
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#include <iomanip>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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using namespace nlohmann::literals;
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int main()
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{
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json j = R"( {"hello": "world", "answer": 42} )"_json;
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std::cout << std::setw(2) << j << '\n';
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}
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```
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Output:
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```
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{
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"answer": 42,
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"hello": "world"
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}
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```
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## See also
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- [Creating JSON values](https://json.nlohmann.me/features/creating_values/index.md) - the article on creating JSON values
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## Version history
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- Added in version 1.0.0.
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- Moved to namespace `nlohmann::literals::json_literals` in 3.11.0.
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- Added `char8_t*` overload in 3.12.x.
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