json/api/macros/json_has_std_format.md

JSON_HAS_STD_FORMAT

#define JSON_HAS_STD_FORMAT /* value */

This macro indicates whether the standard library has support for std::format/std::formatter (that is, the <format> header). Possible values are 1 when supported or 0 when unsupported.

Default definition

The default value is detected based on the preprocessor macros #!cpp JSON_HAS_CPP_20 and #!cpp __cpp_lib_format.

When the macro is not defined, the library will define it to its default value.

Notes

!!! info "Enabled functionality"

When this macro evaluates to `1`, the library provides a
[`std::formatter<basic_json>`](../basic_json/std_formatter.md) specialization so JSON values can be
used directly with `std::format`.

Examples

??? example

The code below forces the library to disable support for `std::format`, even if the standard library
would otherwise support it:

```cpp
#define JSON_HAS_STD_FORMAT 0
#include <nlohmann/json.hpp>

...
```

Version history

• Added in version 3.12.x.