std::vformat_to

From cppreference.com
< cpp‎ | utility‎ | format
 
 
Utilities library
General utilities
Date and time
Function objects
Formatting library (C++20)
(C++11)
Relational operators (deprecated in C++20)
Integer comparison functions
(C++20)(C++20)(C++20)   
(C++20)
Swap and type operations
(C++14)
(C++11)
(C++11)
(C++11)
(C++17)
Common vocabulary types
(C++11)
(C++17)
(C++17)
(C++17)
(C++11)
(C++17)
(C++23)
Elementary string conversions
(C++17)
(C++17)
 
Formatting library
Formatting functions
(C++20)
(C++20)
(C++20)
vformat_to
(C++20)
Formatter
(C++20)
Formatting arguments
Format error
 
Defined in header <format>
template< class OutputIt >
OutputIt vformat_to( OutputIt out, std::string_view fmt, std::format_args args );
(1) (since C++20)
template< class OutputIt >
OutputIt vformat_to( OutputIt out, std::wstring_view fmt, std::wformat_args args );
(2) (since C++20)
template< class OutputIt >

OutputIt vformat_to( OutputIt out, const std::locale& loc,

                     std::string_view fmt, std::format_args args );
(3) (since C++20)
template< class OutputIt >

OutputIt vformat_to( OutputIt out, 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 write the result to the output iterator out. If present, loc is used for locale-specific formatting.

Let CharT be decltype(fmt)::char_type (char for overloads (1,3), wchar_t for overloads (2,4)).

These overloads participate in overload resolution only if OutputIt satisfies the concept std::output_iterator<const CharT&>.

The behavior is undefined if OutputIt does not model (meet the semantic requirements of) the concept std::output_iterator<const CharT&>, or if std::formatter<Ti, CharT> does not meet the Formatter requirements for any Ti in the type of arguments.

Parameters

out - iterator to the output buffer
fmt - string view representing 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.
  • 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 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

Iterator past the end of the output range.

Exceptions

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

Example

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P2216R3 C++20 type of args is parameterized on OutputIt not parameterized

See also