std::print
From cppreference.com
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)
Print functions
Print functions
print
(C++23)
(C++23)
(C++23)(C++23)
(C++23)(C++23)
Defined in header
<print>
template< class... Args >
void print( std::format_string <Args...> fmt, Args&&... args );
(1)
(since C++23)
void print( std::format_string <Args...> fmt, Args&&... args );
template< class... Args >
(2)
(since C++23)
void print( std::FILE * stream,
Format args according to the format string fmt, and print the result to an output stream.
1) Equivalent to std::print(stdout, fmt, std::forward <Args>(args)...).
2) If the ordinary literal encoding is UTF-8, equivalent to (std::enable_nonlocking_formatter_optimization<std::remove_cvref_t <Args>> && ...)
? std::vprint_unicode (stream, fmt.str, std::make_format_args (args...))
: std::vprint_unicode_buffered(stream, fmt.str, std::make_format_args (args...));.
? std::vprint_unicode (stream, fmt.str, std::make_format_args (args...))
: std::vprint_unicode_buffered(stream, fmt.str, std::make_format_args (args...));.
Otherwise, equivalent to (std::enable_nonlocking_formatter_optimization<std::remove_cvref_t <Args>> && ...)
? std::vprint_nonunicode (stream, fmt.str, std::make_format_args (args...))
: std::vprint_nonunicode_buffered(stream, fmt.str, std::make_format_args (args...));.
? std::vprint_nonunicode (stream, fmt.str, std::make_format_args (args...))
: std::vprint_nonunicode_buffered(stream, fmt.str, std::make_format_args (args...));.
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.
[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
same as std::print except that each print is terminated by additional new line
(function template) [edit]
writes out formatted representation of its arguments through an output iterator
(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
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_print |
202207L |
(C++23) | Formatted output |
202403L |
(C++26) (DR23) |
Unbuffered formatted output | |
202406L |
(C++26) (DR23) |
Enabling unbuffered formatted output for more formattable types | |
__cpp_lib_format |
202207L |
(C++23) | Exposing std::basic_format_string |
[edit] Example
Run this code
#include <cstdio> #include <filesystem> #include <print> int main() { std::print("{2} {1}{0}!\n", 23, "C++", "Hello"); // overload (1) const auto tmp{std::filesystem::temp_directory_path () / "test.txt"}; if (std::FILE * stream{std::fopen (tmp.c_str(), "w")}) { std::print(stream, "File: {}", tmp.string()); // overload (2) std::fclose (stream); } }
Output:
Hello C++23!
[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 |
|---|---|---|---|
| P3107R5 | C++23 | only buffered printing operations can be performed | can perform unbuffered printing operations |
| P3235R3 | C++23 | the names of the functions added by P3107R5 were misleading |
changed the function names |
[edit] See also
(C++23)
(function template) [edit]
(C++20)
(function template) [edit]