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std::vprint_unicode, std::vprint_unicode_locking

From cppreference.com
< cpp‎ | io
Defined in header <print>
void vprint_unicode( std::string_view fmt, std::format_args args );
(1) (since C++23)
void vprint_unicode( std::FILE* stream,
                     std::string_view fmt, std::format_args args );
(2) (since C++23)
void vprint_unicode_locking( std::FILE* stream,
                             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) Equivalent to std::vprint_unicode(stdout, fmt, args).
2) Equivalent to std::string out = std::vformat(fmt, args);
std::vprint_unicode_locking(stream, "{}", std::make_format_args(out));
.
3) 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 condition 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.

Contents

[edit] 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

[edit] Exceptions

[edit] 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
__cpp_lib_format 202207L (C++23) Exposing std::basic_format_string

[edit] Example

[edit] See also

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

[edit] External links

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