std::println - cppreference.com (original) (raw)
| Defined in header | ||
|---|---|---|
| template< class... Args > void println( std::format_string<Args...> fmt, Args&&... args ); | (1) | (since C++23) |
| template< class... Args > void println( std::FILE* stream, std::format_string<Args...> fmt, Args&&... args ); | (2) | (since C++23) |
| 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.
Equivalent to std::println(stdout, fmt, std::forward<Args>(args)...).
Equivalent to performing the following operations:
Equivalent to std::println(stdout).
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.
[edit] Parameters
| stream | - | output file stream to write to |
|---|---|---|
| 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 }. 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++23) For other formattable types, the format specification is determined by user-defined formatter specializations. |
| args... | - | arguments to be formatted |
[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
#include 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: