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Difference between revisions of "cpp/io/basic ostream/println"

From cppreference.com
< cpp‎ | io‎ | basic ostream
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===Notes===
 
===Notes===
{{ftm begin|std=1|value=1}}
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{{ftm begin|std=1|value=1|comment=1}}
{{ftm|std=C++23|value=202207L|__cpp_lib_print}}
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{{ftm|std=C++23|value=202207L|__cpp_lib_print|Formatted output}}
{{ftm|std=C++23|value=202207L|__cpp_lib_format}}
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{{ftm|std=C++23|value=202207L|__cpp_lib_format|Exposing {{lc|std::basic_format_string}}}}
 
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Revision as of 05:04, 4 October 2022

 
 
 
 
Defined in header <ostream>
template< class... Args >
  void println( std::ostream& os, std::format_string<Args...> fmt, Args&&... args );
(since C++23)

Formats args according to the format string fmt with appended '\n' (which means that each output ends with a new-line), and inserts the result into os stream.

Equivalent to: std::print(os, "{}\n", std::format(fmt, std::forward<Args>(args)...));

The behavior is undefined if std::formatter<Ti, char> does not meet the BasicFormatter requirements for any Ti in Args (as required by std::make_format_args).

Contents

Parameters

os - output stream to insert data into
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-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

Return value

(none)

Exceptions

Notes

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

Example

See also

outputs formatted representation of the arguments
(function template) [edit]
(C++23)
same as std::print except that each print is terminated by additional new line
(function template) [edit]
(C++20)
stores formatted representation of the arguments in a new string
(function template) [edit]