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std::formatter<pair-or-tuple>
Defined in header <format> |
||
---|---|---|
|
(since C++23) |
The template specialization of std::formatter
for the std::pair
and std::tuple
allows users to convert a pair or a tuple to its textual representation as a collection of elements using formatting functions.
The exposition-only name /*pair-or-tuple*/
denotes either class template std::pair
or std::tuple
.
Format specification
The syntax of tuple-format-spec is:
tuple-fill-and-align (optional) width (optional) tuple-type (optional) |
The tuple-fill-and-align is interpreted the same way as a fill-and-align except that the fill in tuple-fill-and-align is any character other than {
, }
, or :
.
The width is described in standard format width specification.
The tuple-type changes the way a tuple is formatted, with certain options only valid with certain argument types.
The available tuple presentation types are:
m
: Indicates that both opening and closing brackets should be""
while the separator should be": "
.- If
m
is chosen as the tuple-type, the program is ill-formed unlesssizeof...(Ts) == 2
istrue
. n
: Indicates that separator, opening and closing brackets should be""
.
Member objects
Member name | Definition |
---|---|
underlying_ (private) |
tuple of underlying formatters of type std::tuple<std::formatter<std::remove_cvref_t<Ts>, CharT>...> (exposition-only member object*) |
separator_ (private) |
a string representing the separator of the tuple formatted result (the default value is ", " )(exposition-only member object*) |
opening-bracket_ (private) |
a string representing the opening bracket of the tuple formatted result (the default value is "(" )(exposition-only member object*) |
closing-bracket_ (private) |
a string representing the closing bracket of the tuple formatted result (the default value is ")" )(exposition-only member object*) |
Member functions
set_separator
|
sets a specified separator for the tuple formatted result (public member function) |
set_brackets
|
sets a specified opening and closing brackets for the tuple formatted result (public member function) |
parse
|
parses the format specifier as specified by tuple-format-spec (public member function) |
format
|
writes the tuple formatted output as specified by tuple-format-spec (public member function) |
std::formatter<pair-or-tuple>::set_separator
|
Assigns sep
to separator_
.
std::formatter<pair-or-tuple>::set_brackets
|
Assigns opening
and closing
to opening-bracket_
and closing-bracket_
, respectively.
std::formatter<pair-or-tuple>::parse
|
Parses the format specifiers as a tuple-format-spec and stores the parsed specifiers in the current object.
If tuple-type or the n
option is present, the values of opening-bracket
, closing-bracket
, and separator
are modified as required.
For each element e
in underlying_
, calls e.parse(ctx)
to parse an empty format-spec and, if e.set_debug_format()
is a valid expression, calls e.set_debug_format()
.
Returns an iterator past the end of the tuple-format-spec.
std::formatter<pair-or-tuple>::format
|
If (std::formattable<const Ts, CharT> && ...)
is true
, then the type of elems
is const /*pair-or-tuple*/<Ts...>&
. Otherwise, the type is /*pair-or-tuple*/<Ts...>&
.
Writes the following into ctx.out()
as specified by tuple-format-spec, in order:
opening-bracket_
,- for each index
I
in half-open interval[0, sizeof...(Ts))
: - if
I != 0
,separator_
, - the result of writing
get<I>(elems)
viaget<I>(underlying_)
, and closing-bracket_
.
Returns an iterator past the end of the output range.
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
LWG 3892 | C++23 | incorrect formatting of nested ranges | corrected |
See also
(C++20)
|
defines formatting rules for a given type (class template) |
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