< cpp‎ | utility‎ | format
Utilities library
General utilities
Date and time
Function objects
Formatting library (C++20)
Relational operators (deprecated in C++20)
Integer comparison functions
Swap and type operations
Common vocabulary types
Elementary string conversions
Formatting library
Formatting functions
Formatting arguments
Format error
Defined in header <format>
(1) (since C++20)
(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.


[edit] 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-ids 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.
args - arguments to be formatted
loc - std::locale used for locale-specific formatting

[edit] Return value

A string object holding the formatted result.

[edit] 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.

[edit] Example

[edit] See also