std::regex_match

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
Expression	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`	`first`	`str`	`s.begin()`
`m.prefix().matched`	`false`^[1]
`m.suffix().first`	`last`	`std::char_traits<CharT>::length(str) + str`	`s.end()`
`m.suffix().second`	`last`	`std::char_traits<CharT>::length(str) + str`	`s.end()`
`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`	`false` if marked sub-expression `n` did not participate in the match `true` otherwise

The match prefix is empty.
The match suffix is empty.
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)