std::regex_match

 

C++

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Named requirements

Feature test macros (C++20)

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Concepts library (C++20)

Metaprogramming library (C++11)

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Strings library

Containers library

Iterators library

Ranges library (C++20)

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Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

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 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
m.suffix().first	last	std::char_traits<CharT>::     length(str) + str	s.end()
m.suffix().second
m.suffix().matched	false
m[0].first	first	str	s.begin()
m[0].second	last	std::char_traits<CharT>::     length(str) + str	s.end()
m[0].matched	true
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

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

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)