std::match_results::format

Parameters

fmt

Format string.
This may include format specifiers and escape sequences that are replaced by the characters they represent. For format_default, the possible specifiers are:

characters	replacement
$n	n-th backreference (i.e., a copy of the n-th matched group specified with parentheses in the regex pattern). n must be an integer value designating a valid backreference, greater than 1, and of two digits at most.
$&	A copy of the entire match
$`	The prefix (i.e., the part of the target sequence that precedes the match).
$´	The suffix (i.e., the part of the target sequence that follows the match).
$$	A single $ character.

flags

Flags used to interpret the format string.
One or more of these constants can be combined (using the bitwise OR operator, |) to form a valid bitmask value of type regex_constants::match_flag_type:

flag*	effects on format	notes
match_default	Default	Same as format_default. This constant has a value of zero**.
match_not_bol	None	Ignored by this function. See regex_constants for more info.
match_not_eol
match_not_bow
match_not_eow
match_any
match_not_null
match_continuous
match_prev_avail
format_default	Default formatting	Uses the standard formatting rules to replace matches (those used by ECMAScript's replace method). This constant has a value of zero**.
format_sed	sed formatting	Uses the same rules as the sed utility in POSIX to replace matches.
format_no_copy	No copy	The sections in the target sequence that do not match the regular expression are not copied when replacing matches.
format_first_only	First only	Only the first occurrence of a regular expression is replaced.

* These bitmask flag names are available under the std::regex_constants namespace (see regex_constants for more details).
** Constants with a value of zero are ignored if some other flag is set.
match_flag_type is a type available under the std::regex_constants namespace.

out

Output Iterator pointing to a sequence of characters where the resulting string is stored.

fmt_first, fmt_last

Range on a sequence of characters containing the format string.

Return value

Example

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// match_results::format
// - using cmatch, a standard alias of match_results<const char*>
#include <iostream>
#include <regex>

int main ()
{
  std::cmatch m;

  std::regex_match ( "subject", m, std::regex("(sub)(.*)") );

  std::cout << m.format ("the expression matched [$0].\n");
  std::cout << m.format ("with sub-expressions [$1] and [$2].\n");

  return 0;
}

the expression matched [subject].
with sub-expressions [sub] and [ject].

See also

sub_match::str

Return string (public member function)

regex_replace

Replace matched sequence (function template)