NAME¶

std::vprint_unicode,std::vprint_unicode_locking - std::vprint_unicode,std::vprint_unicode_locking

Synopsis¶

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, (3) (since C++23)
std::format_args args );

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:

* If stream refers to a terminal capable of displaying Unicode, flushes stream and
writes out to the terminal using the native Unicode API.
* Otherwise, writes unmodified out to the 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.

Parameters¶

stream - output file stream to write to

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

specifies the index of the argument in args whose value is to
be used for formatting; if it is omitted, the arguments are
arg-id - 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.
fmt - the format specification defined by the std::formatter
format-spec - specialization for the corresponding argument. Cannot start
with }.

* 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 range types, the format specification is interpreted
as range format specification.
* For std::pair and std::tuple, the format specification is
interpreted as tuple format specification.
* For std::thread::id and std::stacktrace_entry, see thread (since C++23)
id format specification and stacktrace entry format
specification.
* For std::basic_stacktrace, no format specifier is
allowed.

* For std::filesystem::path, see path format specification. (since C++26)

* 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¶

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
202207L (C++23) Formatted output
__cpp_lib_print 202403L (C++26) Formatted output with stream locking
(DR23)
__cpp_lib_format 202207L (C++23) Exposing std::basic_format_string

Example¶

This section is incomplete
Reason: no example

See also¶

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

External links¶

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

Category:¶

* Todo no example