std::regex_match

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Regular expressions library

Classes

basic_regex (C++11)

sub_match (C++11)

match_results (C++11)

Algorithms

regex_match (C++11)

regex_search (C++11)

regex_replace (C++11)

Iterators

regex_iterator (C++11)

regex_token_iterator (C++11)

Exceptions

regex_error (C++11)

Traits

regex_traits (C++11)

Constants

syntax_option_type (C++11)

match_flag_type (C++11)

error_type (C++11)

Regex Grammar

Modified ECMAScript-262 (C++11)

 

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 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 );	(4)	(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 );	(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++14)

Determines if the regular expression el 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 BidirectionalIterator.

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
    std::string fnames[] = {"foo.txt", "bar.txt", "baz.dat", "zoidberg"};
    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
    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
    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

See also

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