NAME¶

std::vformat - std::vformat

Synopsis¶

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 (2) (since C++20)
args );
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 (4) (since C++20)
args );

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¶

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

specifies the index of the argument in args whose value is to
be used for formatting; if it is omitted, the arguments are
arg-id - 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.
fmt - the format specification defined by the std::formatter
format-spec - 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. (since C++23)
* 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.

* 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

See also¶