std::println(std::ostream)
From cppreference.com
< cpp | io | basic ostream
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Input/output library
Print functions (C++23)
Buffers
(C++23)
(C++98/26*)
(C++20)
Streams
Abstractions
File I/O
String I/O
Array I/O
(C++23)
(C++23)
(C++23)
(C++98/26*)
(C++98/26*)
(C++98/26*)
Synchronized Output
(C++20)
Types
Error category interface
(C++11)
(C++11)
std::basic_ostream
Member functions Formatted output Unformatted output Positioning Miscellaneous Member classes Non-member functions
Global objects
(C++11)
(C++11)
(C++23)
println(std::ostream)
(C++23)
(C++23)
(C++23)
Defined in header
<ostream>
template< class... Args >
void println( std::ostream & os, std::format_string <Args...> fmt, Args&&... args );
(1)
(since C++23)
void println( std::ostream & os, std::format_string <Args...> fmt, Args&&... args );
void println( std::ostream & os );
(2)
(since C++26)
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.
1) Equivalent to:
std::print (os, "{}\n", std::format (os.getloc(), fmt, args...));
2) Equivalent to:
std::print (os, "\n");
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 ).
[edit] Parameters
os
-
output stream to insert data into
fmt
-
an object that represents the format string. The format string consists of
args...
-
arguments to be formatted
same as std::print except that each print is terminated by additional new line
(function template) [edit]
- 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 }.
- 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 id format specification and stacktrace entry format specification.
- For std::basic_stacktrace, no format specifier is allowed.
(since C++26)
- For other formattable types, the format specification is determined by user-defined
formatterspecializations.
[edit] Exceptions
- std::bad_alloc on allocation failure.
- Propagate any exception thrown by any formatter, e.g. std::format_error , without regard to the value of os.exceptions() and without turning on ios_base::badbit in the error state of os.
- May throw ios_base::failure caused by os.setstate(ios_base::badbit) which is called if an insertion into os fails.
[edit] Notes
Although overload (2) is added in C++26, all known implementations make it available in C++23 mode.
| 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 |
[edit] Example
This section is incomplete
Reason: no example
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 4088 | C++23 | (1) ignored the locale imbued in os in formatting arguments | such locale is used |
[edit] See also
(C++23)
(function template) [edit]