namespace std { template <> struct formatter<nlohmann::basic_json, char>; }
Specialization to make JSON values formattable with std::format (and the other members of C++20's <format> header, such as std::format_to).
A subset of the standard format spec grammar is supported, repurposed for JSON pretty-printing; any other spec component (sign, the 0 flag, precision, L, a dynamic width such as #!cpp "{:{}}", or a trailing type character) throws std::format_error:
#!cpp "{}" serializes the value the same way as dump() (compact, no whitespace).#!cpp "{:#}" (“alternate form”) serializes the value the same way as #!cpp dump(4) (pretty-printed with an indent of 4).#!cpp "#" (e.g. #!cpp "{:2}" or #!cpp "{:#2}"), serializes the value the same way as #!cpp dump(width) — a width on its own implies pretty-printing, since an indent size has no meaning for compact output.fill-and-align (e.g. #!cpp "{:.>#}" or #!cpp "{:.>3}") picks a custom indent character, the same way as #!cpp dump(indent, indent_char). The alignment direction itself (#!cpp '<', #!cpp '>', #!cpp '^') has no separate meaning for JSON values — only the fill character before it is used, and any of the three directions is accepted.This specialization is only available for #!cpp char-based JSON values and only if the standard library provides <format>, controlled by the JSON_HAS_STD_FORMAT macro.
??? example
The example shows how to format JSON values with `std::format`. ```cpp --8<-- "examples/std_formatter.c++20.cpp" ``` Output: ```json --8<-- "examples/std_formatter.c++20.output" ```
fmt::format (fmtlib)