std:: vprint_unicode, std:: vprint_unicode_buffered

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< cpp ‎ | io
C++
Input/output library
Print functions
Print functions
(C++23)
(C++23)
vprint_unicode vprint_unicode_buffered
(C++23) (C++23)
(C++23) (C++23)
Defined in header <print>
void vprint_unicode ( std:: FILE * stream,
std:: string_view fmt, std:: format_args args ) ;
(1) (since C++23)
void vprint_unicode_buffered ( std:: FILE * stream,
std:: string_view fmt, std:: format_args args ) ;
(2) (since C++23)
void vprint_unicode_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) Performs the following operations in order:
  1. Locks stream .
  2. Let out denote the character representation of formatting arguments provided by args formatted according to specifications given in fmt .
  3. Writes out to stream :
Unconditionally unlocks stream on function exit.
If any of the following conditions is satisfied, the behavior is undefined:
  • stream is not a valid pointer to an output C stream.
  • out contains invalid Unicode code units if the native Unicode API is used.
2) Equivalent to std:: string out = std:: vformat ( fmt, args ) ;
std :: vprint_unicode ( stream, "{}" , std:: make_format_args ( out ) ) ; .
3) Equivalent to std :: vprint_unicode_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)
(since C++26)
  • For other formattable types, the format specification is determined by user-defined formatter specializations.
args - arguments to be formatted

Exceptions

Notes

The C++ standard encourages the implementers to produce a diagnostic message if out contains invalid Unicode code units.

On POSIX, the stream refers to a terminal if the expression isatty ( fileno ( stream ) ) ! = 0 holds true (see POSIX documentation for isatty , and fileno ).

On Windows, the stream refers to a terminal if the expression GetConsoleMode ( _get_osfhandle ( _fileno ( stream ) ) ) returns nonzero (see Windows documentation for GetConsoleMode , _get_osfhandle , and _fileno ). The native Unicode API on Windows is WriteConsoleW .

If invoking the native Unicode API requires transcoding, the invalid code units are substituted with U+FFFD REPLACEMENT CHARACTER (see "The Unicode Standard Version 14.0 - Core Specification", Chapter 3.9 ).

Feature-test macro Value Std Feature
__cpp_lib_print 202207L (C++23) Formatted output
202403L (C++26)
(DR23) 		Formatted output with stream locking
202406L (C++26)
(DR23) 		Enabling nonlocking formatter optimization for more formattable types
__cpp_lib_format 202207L (C++23) Exposing std::basic_format_string

Example

This section is incomplete
Reason: no example

See also

(C++23)
prints to stdout or a file stream using type-erased argument representation
(function)
(C++23)
performs Unicode aware output using type-erased argument representation
(function)
(C++23)
prints to stdout or a file stream using formatted representation of the arguments
(function template)
(C++20)
stores formatted representation of the arguments in a new string
(function template)

External links

1. Unicode
2. The Unicode Standard Version 14.0 - Core Specification
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