20 General utilities library [utilities]

20.20 Formatting [format]

20.20.5 Formatter [format.formatter] Formatter requirements [formatter.requirements]

A type F meets the Formatter requirements if:
Given character type charT, output iterator type Out, and formatting argument type T, in Table 67:
  • f is a value of type F,
  • u is an lvalue of type T,
  • t is a value of a type convertible to (possibly const) T,
  • PC is basic_­format_­parse_­context<charT>,
  • FC is basic_­format_­context<Out, charT>,
  • pc is an lvalue of type PC, and
  • fc is an lvalue of type FC.
pc.begin() points to the beginning of the format-spec ([format.string]) of the replacement field being formatted in the format string.
If format-spec is empty then either pc.begin() == pc.end() or *pc.begin() == '}'.
Table 67: Formatter requirements [tab:formatter]
Return type
Parses format-spec ([format.string]) for type T in the range [pc.begin(), pc.end()) until the first unmatched character.
Throws format_­error unless the whole range is parsed or the unmatched character is }.
[Note 1:
This allows formatters to emit meaningful error messages.
— end note]
Stores the parsed format specifiers in *this and returns an iterator past the end of the parsed range.
f.format(t, fc)
Formats t according to the specifiers stored in *this, writes the output to fc.out() and returns an iterator past the end of the output range.
The output shall only depend on t, fc.locale(), and the range [pc.begin(), pc.end()) from the last call to f.parse(pc).
f.format(u, fc)
As above, but does not modify u.