NAME¶

std::regex_match - std::regex_match

Synopsis¶

Defined in header <regex>
template< class BidirIt,

class Alloc, class CharT, class Traits >
bool regex_match( BidirIt first, BidirIt last, (since
std::match_results<BidirIt,Alloc>& m, (1) C++11)
const std::basic_regex<CharT,Traits>& e,
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
template< class BidirIt,

class CharT, class Traits >
bool regex_match( BidirIt first, BidirIt last, (2) (since
const std::basic_regex<CharT,Traits>& e, C++11)
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
template< class CharT, class Alloc, class Traits >

bool regex_match( const CharT* str,
std::match_results<const CharT*,Alloc>& m, (3) (since
const std::basic_regex<CharT,Traits>& e, C++11)
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
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, (4) (since
Alloc C++11)
>& m,
const std::basic_regex<CharT,Traits>& e,
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
template< class CharT, class Traits >

bool regex_match( const CharT* str, (since
const std::basic_regex<CharT,Traits>& e, (5) C++11)
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
template< class STraits, class SAlloc,

class CharT, class Traits >
bool regex_match( const std::basic_string<CharT, STraits, SAlloc>& s, (6) (since
const std::basic_regex<CharT,Traits>& e, C++11)
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
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, (7) (since
Alloc C++11)
>&,
const std::basic_regex<CharT,Traits>&,
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default ) = delete;

Determines if the regular expression e 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 LegacyBidirectionalIterator.

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
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 (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
basic_string rvalues were accepted, which rejected via a deleted
LWG 2329 C++11 was likely to result in dangling overload
iterators

See also¶

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