std::vprint_unicode(std::ostream)

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vprint_unicode(std::ostream)

(C++23)

vprint_nonunicode(std::ostream)

(C++23)

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Defined in header`<ostream>`
void vprint_unicode(std::ostream& os, std::string_view fmt,std::format_args args);		(since C++23)

Formatargs according to the format stringfmt, and writes the result to the output streamos. Behaves asFormattedOutputFunction ofos, except that some details of error reportingdiffer.

Performs the following operations in order:

First, the function constructs and checks thesentry object.
Initializes an automatic variable as if bystd::string out=std::vformat(os.getloc(), fmt, args);.
Writesout toos:

Ifos refers to a terminal that is only capable of displaying Unicode via anative Unicode API, flushesos and writesout to the terminal using the native Unicode API.
Otherwise, inserts the character sequence[out.begin(), out.end()) intoos.

If writing to the terminal or inserting intoos fails, callsos.setstate(std::ios_base::badbit).

After writing characters toos, establishes anobservable checkpoint.

(since C++26)

Ifout contains invalid Unicodecode units when the native Unicode API is used, the behavior is undefined.

[edit]Parameters

os - output stream to insert data into

fmt

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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. Thearg-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 thestd::formatter specialization for the corresponding argument. Cannot start with}.

For basic types and standard string types, the format specification is interpreted asstandard format specification.
For chrono types, the format specification is interpreted aschrono format specification.

For range types, the format specification is interpreted asrange format specification.
Forstd::pair andstd::tuple, the format specification is interpreted astuple format specification.
Forstd::thread::id andstd::stacktrace_entry, seethread id format specification andstacktrace entry format specification.
Forstd::basic_stacktrace, no format specifier is allowed.

(since C++23)

Forstd::filesystem::path, seepath format specification.

(since C++26)

For other formattable types, the format specification is determined by user-definedformatter specializations.

args - arguments to be formatted

[edit]Exceptions

std::bad_alloc on allocation failure.
Propagate any exception thrown by anyformatter, e.g.std::format_error, without regard to the value ofos.exceptions() and without turning onios_base::badbit in the error state ofos.
May throwios_base::failure caused byos.setstate(ios_base::badbit) which is called if an insertion intoos fails.

[edit]Notes

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

Feature-test macro	Value	Std	Feature
`__cpp_lib_print`	`202207L`	(C++23)	Formatted output
`__cpp_lib_format`	`202207L`	(C++23)	Exposingstd::basic_format_string

[edit]Example

This section is incomplete
Reason: no example

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 4044	C++23	the native Unicode API was always used if the terminal referred to byos can display Unicode	only used if the terminal can only use the native Unicode API to display Unicode

[edit]See also

vprint_nonunicode(std::ostream) (C++23)	outputs character data usingtype-erased argument representation (function)[edit]
print(std::ostream) (C++23)	outputsformatted representation of the arguments (function template)[edit]
operator<<(std::basic_ostream)	inserts character data or insert into rvalue stream (function template)[edit]
vprint_unicodevprint_unicode_buffered (C++23)	prints to Unicode capablestdout or a file stream usingtype-erased argument representation (function)[edit]
format (C++20)	stores formatted representation of the arguments in a new string (function template)[edit]