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std::vprint_unicode(std::ostream)

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< cpp‎ | io‎ | basic ostream
 
C++
 
Input/output library
 
std::basic_ostream
 
Defined in header <ostream>
void vprint_unicode( std::ostream& os,
                     std::string_view fmt, std::format_args args );
 (since C++23)

Format args according to the format string fmt, and writes the result to the output stream os. Behaves as FormattedOutputFunction of os, except that some details of error reporting differ.

Performs the following operations in order:

  1. First, the function constructs and checks the sentry object.
  2. Initializes an automatic variable as if by std::string out = std::vformat(os.getloc(), fmt, args);.
  3. Writes out to os:
  • If os refers to a terminal that is only capable of displaying Unicode via a native Unicode API, flushes os and writes out to the terminal using the native Unicode API.
  • Otherwise, inserts the character sequence [out.begin(), out.end()) into os.

If writing to the terminal or inserting into os fails, calls os.setstate(std::ios_base::badbit).

After writing characters to os, establishes an observable checkpoint.

(since C++26)

If out contains invalid Unicode code units when the native Unicode API is used, the behavior is undefined.

Contents

[edit] Parameters

os - output stream to insert data into
fmt -
[edit]
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

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

Feature-test macro Value Std Feature