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std::vprint_nonunicode, std::vprint_nonunicode_buffered - cppreference.com

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Defined in header <print>

void vprint_nonunicode( std::FILE* stream, std::string_view fmt, std::format_args args );

 (1) (since C++23)

void vprint_nonunicode_buffered ( std::FILE* stream, std::string_view fmt, std::format_args args );

 (2) (since C++23)

void vprint_nonunicode_buffered ( std::string_view fmt, std::format_args args );

 (3) (since C++23)

Format args according to the format string fmt, and writes the result to the output stream.

1) While holding the lock on stream, writes the character representation of formatting arguments provided by args formatted according to specifications given in fmt to stream.

If stream is not a valid pointer to an output C stream, the behavior is undefined.

2) Equivalent to std::string out = std::vformat(fmt, args);
std::vprint_nonunicode(stream, "{}", std::make_format_args(out));.

3) Equivalent to std::vprint_nonunicode_buffered(stdout, fmt, args).

Parameters

stream - output file stream to write to
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-id s 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. Cannot start with }.
(since C++23)
  • For other formattable types, the format specification is determined by user-defined formatter specializations.
args - arguments to be formatted

Exceptions

  • std::bad_alloc on allocation failure.
  • std::system_error, if writing to the stream fails.
  • Propagates any exception thrown by used formatters, e.g. std::format_error.

Notes

Feature-test macro Value Std Feature
__cpp_lib_print 202207L (C++23) Formatted output
202403L (C++26)
(DR23)		 Unbuffered formatted output
202406L (C++26)
(DR23)		 Enabling unbuffered formatted output for more formattable types
__cpp_lib_format 202207L (C++23) Exposing std::basic_format_string

Example

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P3107R5 C++23 printing operations were always buffered provides unbuffered printing operations
P3235R3 C++23 the names of the functions added
by P3107R5 were misleading 		changed the function names

See also