std::println
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(C++23)
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Print functions
(C++23)
println
(C++23)
(C++23)(C++23)
(C++23)(C++23)
Defined in header
<print>
template< class... Args >
void println( std::format_string <Args...> fmt, Args&&... args );
(1)
(since C++23)
void println( std::format_string <Args...> fmt, Args&&... args );
template< class... Args >
(2)
(since C++23)
void println( std::FILE * stream,
void println();
(3)
(since C++26)
void println( std::FILE * stream );
(4)
(since C++26)
Format args according to the format string fmt with appended '\n' (which means that each output ends with a new-line), and print the result to a stream.
1) Equivalent to std::println(stdout, fmt, std::forward <Args>(args)...).
2) Equivalent to performing the following operations:
std::print (stream, "{}\n", std::format (fmt, std::forward <Args>(args)...));
(until C++26)std::print (stream, std::runtime_format (std::string (fmt.get()) + '\n'),
std::forward <Args>(args)...)
3) Equivalent to std::println(stdout).
4) Equivalent to std::print (stream, "\n").
If std::formatter <Ti, char> does not meet the BasicFormatter requirements for any Ti in Args (as required by std::make_format_args ), the behavior is undefined.
Contents
[edit] Parameters
stream
-
output file stream to write to
fmt
-
an object that represents the format string. The format string consists of
args...
-
arguments to be formatted
prints to stdout or a file stream using formatted representation of the arguments
(function template) [edit]
outputs formatted representation of the arguments with appended '\n'
(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.
- std::system_error , if writing to the stream fails.
- Propagates any exception thrown by used formatters, e.g. std::format_error .
[edit] Notes
Although overloads (3,4) are added in C++26, all known implementations make them available in C++23 mode.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_print |
202207L |
(C++23) | Formatted output |
202403L |
(C++26) | Unbuffered formatted output[1] | |
__cpp_lib_format |
202207L |
(C++23) | Exposing std::basic_format_string |
- ↑ Although P3107R5 is accepted as a DR, std::runtime_format is only available since C++26. As a result, the resolution cannot be applied in C++23.
[edit] Example
Run this code
#include <print> int main() { // Each call to std::println ends with new-line std::println("Please"); // overload (1) std::println("enter"); // (1) std::print ("pass"); std::print ("word"); std::println(); // (3); valid since C++26; same effect as std::print("\n"); }
Output:
Please enter password
[edit] See also
(C++23)
(function template) [edit]
(C++23)
(function template) [edit]