JSON_USE_GLOBAL_UDLS¶
#define JSON_USE_GLOBAL_UDLS /* value */
When defined to 1, the user-defined string literals (UDLs) are placed into the global namespace instead of nlohmann::literals::json_literals.
Default definition¶
The default value is 1.
#define JSON_USE_GLOBAL_UDLS 1
When the macro is not defined, the library will define it to its default value.
Notes¶
Future behavior change
The user-defined string literals will be removed from the global namespace in the next major release of the library.
To prepare existing code, define JSON_USE_GLOBAL_UDLS to 0 and bring the string literals into scope where needed. Refer to any of the string literals for details.
CMake option
The placement of user-defined string literals can also be controlled with the CMake option JSON_GlobalUDLs (ON by default) which defines JSON_USE_GLOBAL_UDLS accordingly.
Examples¶
Example 1: Default behavior
The code below shows the default behavior using the _json UDL.
#include <nlohmann/json.hpp>
#include <iostream>
int main()
{
auto j = "42"_json;
std::cout << j << std::endl;
}
Output:
42
Example 2: Namespaced UDLs
The code below shows how UDLs need to be brought into scope before using _json when JSON_USE_GLOBAL_UDLS is defined to 0.
#define JSON_USE_GLOBAL_UDLS 0
#include <nlohmann/json.hpp>
#include <iostream>
int main()
{
// auto j = "42"_json; // This line would fail to compile,
// because the UDLs are not in the global namespace
// Bring the UDLs into scope
using namespace nlohmann::json_literals;
auto j = "42"_json;
std::cout << j << std::endl;
}
Output:
42
See also¶
Version history¶
- Added in version 3.11.0.