std::vprint_unicode

< cpp‎ | io

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( std::string_view fmt, std::format_args args );	(2)	(since C++23)

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

Let out be a temporary string produced by formatting the arguments in args with std::vformat(fmt, args).

1) If stream refers to a terminal capable of displaying Unicode, writes out to this terminal using the native Unicode API. Otherwise, writes unmodified out to the stream.

2) same as (1) when stream is equal to the standard C output stream stdout, i.e.

std::vprint_unicode(stdout, fmt, args);

The behavior is undefined if:

stream is not a valid pointer to a C stream;
out contains invalid Unicode code units.

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-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 std::thread::id, the format specification is interpreted as thread id format specification.
For other formattable types, the format specification is determined by user-defined formatter specializations.

args - arguments to be formatted

Return value

(none)

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

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	Comment
`__cpp_lib_print`	202207L	(C++23)	Formatted output
`__cpp_lib_format`	202207L	(C++23)	Exposing std::basic_format_string

Example

This section is incomplete
Reason: no example

External links

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

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