std::regex_match
| Defined in header <regex>
|
||
| template< class BidirIt, class Alloc, class CharT, class Traits > |
(1) | (since C++11) |
| template< class BidirIt, class CharT, class Traits > |
(2) | (since C++11) |
| template< class CharT, class Alloc, class Traits > bool regex_match( const CharT* str, |
(3) | (since C++11) |
| template< class STraits, class SAlloc, class Alloc, class CharT, class Traits > |
(4) | (since C++11) |
| template< class CharT, class Traits > bool regex_match( const CharT* str, |
(5) | (since C++11) |
| template< class STraits, class SAlloc, class CharT, class Traits > |
(6) | (since C++11) |
| template< class STraits, class SAlloc, class Alloc, class CharT, class Traits > |
(7) | (since C++11) |
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.
[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.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
#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 2329 | C++11 | basic_string rvalues were accepted, which was likely to result in dangling iterators
|
rejected via a deleted overload |
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) |