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Niels Lohmann
6fc0d501f3
* Add JSON_NO_UDLS to leave out the user-defined string literals The bodies of operator""_json and operator""_json_pointer call the parser, so every translation unit including the library instantiates it, even if it never parses anything. Defining JSON_NO_UDLS leaves the literals out entirely, which saves 15-35% compile time for such translation units (#5294). Nothing changes if the macro is not defined. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Mention JSON_NO_UDLS in the list of exported module symbols Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Move the user-defined string literals to <nlohmann/json_literals.hpp> Following the review in #5294, the literals now live in their own header instead of being removed entirely: <nlohmann/json.hpp> includes it at the end unless JSON_NO_AUTOMATIC_UDLS (renamed from JSON_NO_UDLS) is defined, so a project can opt out globally and include the header only where the literals are used. The header only uses public and standard macros, because the library's internal macros are undefined at the end of json.hpp and the amalgamation inlines macro_scope.hpp only once. For the same reason, the library no longer defines and undefines JSON_USE_GLOBAL_UDLS, so a user's definition is still visible to the header. The single-header copy is identical to the multi-header one, as it only includes <nlohmann/json.hpp>. The module always exports the literals. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Fix CI: include cycle, GCC 4.8 literal operator spacing, and global UDLs off in the JSON_NO_AUTOMATIC_UDLS test - Suppress clang-tidy misc-header-include-cycle on the intentional mutual include of json.hpp and json_literals.hpp. - Use operator"" _json with a space for GCC 4.8 in the test's detection aliases, as the header does. - Only test the global literal operators when JSON_USE_GLOBAL_UDLS is on. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Declare the literal operators through a local macro The GCC 4.8 spacing condition was repeated for both operator definitions and the global using-declarations. NLOHMANN_JSON_LITERAL_OPERATOR(suffix) now selects operator""##suffix or operator"" suffix in one place and is undefined at the end of json_literals.hpp. Suggested by gregmarr in review. Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
1.9 KiB
1.9 KiB
nlohmann::operator""_json
json operator ""_json(const char* s, std::size_t n);
json operator ""_json(const char8_t* s, std::size_t n); // since C++20
This operator implements a user-defined string literal for JSON objects. It can be used by adding #!cpp _json to a
string literal and returns a json object if no parse error occurred.
It is recommended to bring the operator into scope using any of the following lines:
using nlohmann::literals::operator ""_json;
using namespace nlohmann::literals;
using namespace nlohmann::json_literals;
using namespace nlohmann::literals::json_literals;
using namespace nlohmann;
This is suggested to ease migration to the next major version release of the library. See
JSON_USE_GLOBAL_UDLS for details. The operator is declared in header
<nlohmann/json_literals.hpp>, which <nlohmann/json.hpp> includes unless
JSON_NO_AUTOMATIC_UDLS is defined.
Parameters
s(in)- a string representation of a JSON object
n(in)- length of string
s
Return value
json value parsed from s
Exceptions
The function can throw anything that parse(s, s+n) would throw.
Complexity
Linear.
Examples
??? example
The following code shows how to create JSON values from string literals.
```cpp
--8<-- "examples/operator_literal_json.cpp"
```
Output:
```json
--8<-- "examples/operator_literal_json.output"
```
See also
- Creating JSON values - the article on creating JSON values
- JSON_NO_AUTOMATIC_UDLS - do not include the user-defined string literals automatically
Version history
- Added in version 1.0.0.
- Moved to namespace
nlohmann::literals::json_literalsin 3.11.0. - Added
char8_t*overload in 3.13.0.