std::vprint_unicode

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Input/output library

I/O manipulators

Print functions (C++23)

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (deprecated in C++98)

basic_syncbuf (C++20)

Streams

Abstractions

ios_base

basic_ios

basic_istream

basic_ostream

basic_iostream

File I/O

basic_ifstream

basic_ofstream

basic_fstream

String I/O

basic_istringstream

basic_ostringstream

basic_stringstream

Array I/O

basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (deprecated in C++98)

ostrstream (deprecated in C++98)

strstream (deprecated in C++98)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

Print functions

Print functions

print (C++23)

println (C++23)

vprint_unicode (C++23)

vprint_nonunicode (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( 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

See also

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)

External links

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