Defined in header <ostream>
template< class... Args >
  void print( std::ostream& os, std::format_string<Args...> fmt, Args&&... args );
(since C++23)

Formats args according to the format string fmt, and inserts the result into os stream.

If ordinary literal encoding of fmt or any parameter in args... is UTF-8 (where applicable), equivalent to:

std::vprint_unicode(os, fmt.get(), std::make_format_args(std::forward<Args>(args)...));

Otherwise, equivalent to:

std::vprint_nonunicode(os, fmt.get(), std::make_format_args(std::forward<Args>(args)...));

The behavior is undefined if std::formatter<Ti, char> does not model std::formattable for any Ti in Args (as required by std::make_format_args).


os - output stream to insert data into
fmt - an object that represents the format string. The format string consists of
  • ordinary characters (except { and }), which are copied unchanged to the output,
  • escape sequences {{ and }}, which are replaced with { and } respectively in the output, and
  • replacement fields.

Each replacement field has the following format:

{ arg-id (optional) } (1)
{ arg-id (optional) : format-spec } (2)
1) replacement field without a format specification 2) replacement field with a format specification
arg-id - specifies the index of the argument in args whose value is to be used for formatting; if it is omitted, the arguments are used in order.

The arg-ids in a format string must all be present or all be omitted. Mixing manual and automatic indexing is an error.

format-spec - the format specification defined by the std::formatter specialization for the corresponding argument.
  • For basic types and standard string types, the format specification is interpreted as standard format specification.
  • For chrono types, the format specification is interpreted as chrono format specification.
  • For other formattable types, the format specification is determined by user-defined formatter specializations.
args... - arguments to be formatted

Return value




Feature-test macro Value Std
__cpp_lib_print 202207L (C++23)
__cpp_lib_format 202207L (C++23)


See also

outputs formatted representation of the arguments with appended '\n'
(function template)
prints to stdout or a file stream using formatted representation of the arguments
(function template)
stores formatted representation of the arguments in a new string
(function template)

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