std::vformat

 

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visit_format_arg (C++20) (deprecated in C++26)

make_format_argsmake_wformat_args (C++20)(C++20)

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format_error (C++20)

 

Defined in header <format>
std::string vformat( std::string_view fmt, std::format_args args );	(1)	(since C++20)
std::wstring vformat( std::wstring_view fmt, std::wformat_args args );	(2)	(since C++20)
std::string vformat( const std::locale& loc,                      std::string_view fmt, std::format_args args );	(3)	(since C++20)
std::wstring vformat( const std::locale& loc,                       std::wstring_view fmt, std::wformat_args args );	(4)	(since C++20)

Format arguments held by args according to the format string fmt, and return the result as a string. If present, loc is used for locale-specific formatting.

Parameters

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 std::filesystem::path, see path format specification. (since C++26) For other formattable types, the format specification is determined by user-defined formatter specializations.
args	-	arguments to be formatted
loc	-	std::locale used for locale-specific formatting

Return value

A string object holding the formatted result.

Exceptions

Throws std::format_error if fmt is not a valid format string for the provided arguments, or std::bad_alloc on allocation failure. Also propagates any exception thrown by formatter or iterator operations.

Example

Run this code

#include <format>
#include <iostream>
 
template<typename... Args>
inline void println(const std::format_string<Args...> fmt, Args&&... args)
{
    std::cout << std::vformat(fmt.get(), std::make_format_args(args...)) << '\n';
}
 
int main()
{
    println("{}{} {}{}", "Hello", ',', "C++", -1 + 2 * 3 * 4);
}

Output:

Hello, C++23