std::regex_match

From cppreference.com
< cpp‎ | regex
C++
Text processing library
Regular expressions library
Classes
(C++11)
(C++11)
(C++11)
Algorithms
regex_match
(C++11)
(C++11)
(C++11)
Iterators
(C++11)
(C++11)
Exceptions
(C++11)
Traits
(C++11)
Constants
(C++11)
(C++11)
(C++11)
Regex Grammar
(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 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

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

If BidirIt does not satisfy the requirements of LegacyBidirectionalIterator

(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

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
  • the start of the sequence otherwise matching sub-expression n otherwise
m [n] .second
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

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)
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/regex/regex_match&oldid=177664