std:: regex_match

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C++
Regular expressions library
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regex_match
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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 ) .

If BidirIt does not satisfy the requirements of LegacyBidirectionalIterator , the behavior is undefined.

(until C++23)

If BidirIt does not model bidirectional_iterator , the behavior is undefined.

(since C++23)
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

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
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

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