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std::regex_match - cppreference.com

From cppreference.com

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

Determines if the regular expression e matches the entire target character sequence. The detailed match result is stored in m (if present).

1,2) The target character sequence is represented by the range [first, last).

3,4) The target character sequence is represented by the range [str, str + std::char_traits<CharT>::length(str)).

5,6) The target character sequence is represented by the string s.

7) The target character sequence cannot be represented by a std::string rvalue.

If the match does not exist, the following expressions involving m (if exists) should yield the specified values:

 Expression   Value 
m.ready() true
m.size() 0
m.empty() true

If the match exists, given any integer in (​0, m.size()) as n, the following expressions involving m should yield the specified values for each overload listed below:

      Expression       Value
           Overload (1)                       Overload (3)                       Overload (5)           
m.ready() true
m.size() 1 + e.mark_count()
m.empty() false
m.prefix().first first str s.begin()
m.prefix().second
m.prefix().matched     false[1]
m.suffix().first last std::char_traits<CharT>::
length(str) + str 		s.end()
m.suffix().second
m.suffix().matched     false[2]
m[0].first first str s.begin()
m[0].second last std::char_traits<CharT>::
length(str) + str 		s.end()
m[0].matched     true[3]
m[n].first
  • last if marked sub-expression n did not participate in the match
  • the start of the sequence otherwise matching sub-expression n otherwise
m[n].second
  • last if marked sub-expression n did not participate in the match
  • the end of the sequence otherwise matching sub-expression n otherwise
m[n].matched
  1. ↑ The match prefix is empty.
  2. ↑ The match suffix is empty.
  3. ↑ The entire sequence is matched.

Parameters

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

Return value

Returns true if the entire target sequence matches e, 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

#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
LWG 2205 C++11 n could be zero in the postcondition can only be positive
LWG 2273 C++11 it was unclear whether partial matches are considered only considers full matches
LWG 2329 C++11 overload (5) accepted basic_string rvalues,
which could result in dangling iterators 		rejected via deleted overload (7)

See also

regular expression object
(class template) [edit]
identifies one regular expression match, including all sub-expression matches
(class template) [edit]
attempts to match a regular expression to any part of a character sequence
(function template) [edit]