std::regex_match (3) - Linux Manuals

std::regex_match: std::regex_match

NAME

std::regex_match - std::regex_match

Synopsis

Defined in header <regex>
template< class BidirIt,
class Alloc, class CharT, class Traits >
bool regex_match( BidirIt first, BidirIt last,
std::match_results<BidirIt,Alloc>& m, (1) (since C++11)
const std::basic_regex<CharT,Traits>& e,
std::regex_constants::match_flag_type flags =
std::regex_constants::match_default );
template< class BidirIt,
class CharT, class Traits >
bool regex_match( BidirIt first, BidirIt last, (2) (since C++11)
const std::basic_regex<CharT,Traits>& e,
std::regex_constants::match_flag_type flags =
std::regex_constants::match_default );
template< class CharT, class Alloc, class Traits >
bool regex_match( const CharT* str,
std::match_results<const CharT*,Alloc>& m, (3) (since C++11)
const std::basic_regex<CharT,Traits>& e,
std::regex_constants::match_flag_type flags =
std::regex_constants::match_default );
template< class STraits, class SAlloc,
class Alloc, class CharT, class Traits >
bool regex_match( const std::basic_string<CharT,STraits,SAlloc>& s,
std::match_results<
typename std::basic_string<CharT,STraits,SAlloc>::const_iterator, (4) (since C++11)
Alloc
>& m,
const std::basic_regex<CharT,Traits>& e,
std::regex_constants::match_flag_type flags =
std::regex_constants::match_default );
template< class CharT, class Traits >
bool regex_match( const CharT* str,
const std::basic_regex<CharT,Traits>& e, (5) (since C++11)
std::regex_constants::match_flag_type flags =
std::regex_constants::match_default );
template< class STraits, class SAlloc,
class CharT, class Traits >
bool regex_match( const std::basic_string<CharT, STraits, SAlloc>& s, (6) (since C++11)
const std::basic_regex<CharT,Traits>& e,
std::regex_constants::match_flag_type flags =
std::regex_constants::match_default );
template< class STraits, class SAlloc,
class Alloc, class CharT, class Traits >
bool regex_match( const std::basic_string<CharT,STraits,SAlloc>&&,
std::match_results<
typename std::basic_string<CharT,STraits,SAlloc>::const_iterator, (7) (since C++14)
Alloc
>&,
const std::basic_regex<CharT,Traits>&,
std::regex_constants::match_flag_type flags =
std::regex_constants::match_default ) = delete;

Determines if the regular expression e matches the entire target character sequence, which may be specified as std::string, a C-string, or an iterator pair.
1) Determines if there is a match between the regular expression e and the entire target character sequence [first,last), taking into account the effect of flags. When determining if there is a match, only potential matches that match the entire character sequence are considered. Match results are returned in m.
2) Behaves as (1) above, omitting the match results.
3) Returns std::regex_match(str, str + std::char_traits<charT>::length(str), m, e, flags).
4) Returns std::regex_match(s.begin(), s.end(), m, e, flags).
5) Returns std::regex_match(str, str + std::char_traits<charT>::length(str), e, flags).
6) Returns std::regex_match(s.begin(), s.end(), e, flags).
7) The overload 4 is prohibited from accepting temporary strings, otherwise this function populates match_results m with string iterators that become invalid immediately.
Note that regex_match will only successfully match a regular expression to an entire character sequence, whereas std::regex_search will successfully match subsequences.

Parameters

first, last - the target character range to apply the regex to, given as iterators
m - the match results
str - the target string, given as a null-terminated C-style string
s - the target string, given as a std::basic_string
e - the regular expression
flags - flags used to determine how the match will be performed

Type requirements

-
BidirIt must meet the requirements of LegacyBidirectionalIterator.

Return value

Returns true if a match exists, false otherwise. In either case, the object m is updated, as follows:
If the match does not exist:

m.ready() == true
m.empty() == true
m.size() == 0

If the match exists:

m.ready() true
m.empty() false
m.size() number_of_marked_subexpressions plus 1, that is, 1+e.mark_count()
m.prefix().first first
m.prefix().second first
m.prefix().matched false (the match prefix is empty)
m.suffix().first last
m.suffix().second last
m.suffix().matched false (the match suffix is empty)
m[0].first first
m[0].second last
m[0].matched true (the entire sequence is matched)
m[n].first the start of the sequence that matched marked_sub-expression n, or last if the subexpression did not participate in the match
m[n].second the end of the sequence that matched marked_sub-expression n, or last if the subexpression did not participate in the match
m[n].matched true if sub-expression n participated in the match, false otherwise

Notes

Because regex_match only considers full matches, the same regex may give different matches between regex_match and std::regex_search:

  std::regex re("Get|GetValue");
  std::cmatch m;
  std::regex_search("GetValue", m, re); // returns true, and m[0] contains "Get"
  std::regex_match ("GetValue", m, re); // returns true, and m[0] contains "GetValue"
  std::regex_search("GetValues", m, re); // returns true, and m[0] contains "Get"
  std::regex_match ("GetValues", m, re); // returns false

Example

// Run this code

  #include <iostream>
  #include <string>
  #include <regex>

  int main()
  {
      // Simple regular expression matching
      const std::string fnames[] = {"foo.txt", "bar.txt", "baz.dat", "zoidberg"};
      const std::regex txt_regex("[a-z]+\\.txt");

      for (const auto &fname : fnames) {
          std::cout << fname << ": " << std::regex_match(fname, txt_regex) << '\n';
      }

      // Extraction of a sub-match
      const std::regex base_regex("([a-z]+)\\.txt");
      std::smatch base_match;

      for (const auto &fname : fnames) {
          if (std::regex_match(fname, base_match, base_regex)) {
              // The first sub_match is the whole string; the next
              // sub_match is the first parenthesized expression.
              if (base_match.size() == 2) {
                  std::ssub_match base_sub_match = base_match[1];
                  std::string base = base_sub_match.str();
                  std::cout << fname << " has a base of " << base << '\n';
              }
          }
      }

      // Extraction of several sub-matches
      const std::regex pieces_regex("([a-z]+)\\.([a-z]+)");
      std::smatch pieces_match;

      for (const auto &fname : fnames) {
          if (std::regex_match(fname, pieces_match, pieces_regex)) {
              std::cout << fname << '\n';
              for (size_t i = 0; i < pieces_match.size(); ++i) {
                  std::ssub_match sub_match = pieces_match[i];
                  std::string piece = sub_match.str();
                  std::cout << " submatch " << i << ": " << piece << '\n';
              }
          }
      }
  }

Output:

  foo.txt: 1
  bar.txt: 1
  baz.dat: 0
  zoidberg: 0
  foo.txt has a base of foo
  bar.txt has a base of bar
  foo.txt
    submatch 0: foo.txt
    submatch 1: foo
    submatch 2: txt
  bar.txt
    submatch 0: bar.txt
    submatch 1: bar
    submatch 2: txt
  baz.dat
    submatch 0: baz.dat
    submatch 1: baz
    submatch 2: dat