std::regex_match(3)

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, (4) (since C++11)
   SAlloc>::
                        const_iterator,
                        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>:: (7) (since C++11)
                        const_iterator,
                        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 <cstddef>
 #include <iostream>
 #include <regex>
 #include <string>
 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 (std::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
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
                       basic_string rvalues were accepted, which rejected via a deleted
   LWG 2329 C++11 was likely to result in dangling overload
                       iterators

See also
   basic_regex regular expression object
   (C++11) (class template)
   match_results identifies one regular expression match, including all sub-expression
   (C++11) matches
                 (class template)
   regex_search attempts to match a regular expression to any part of a character
   (C++11) sequence
                 (function template)