std::regex_match
| Defined in header <regex>
|
||
| template< class BidirIt, class Alloc, class CharT, class Traits > bool regex_match( BidirIt first, BidirIt last, |
(1) | (since C++11) |
| template< class BidirIt, class CharT, class Traits > bool regex_match( BidirIt first, BidirIt last, |
(2) | (since C++11) |
| template< class CharT, class Alloc, class Traits > bool regex_match( const CharT* str, |
(3) | (since C++11) |
| template< class CharT, class Traits > bool regex_match( const CharT* str, const std::basic_regex<CharT, Traits>& e, |
(4) | (since C++11) |
| template< class STraits, class SAlloc, class Alloc, class CharT, class Traits > |
(5) | (since C++11) |
| template< class STraits, class SAlloc, class CharT, class Traits > bool regex_match( const std::basic_string<CharT, STraits, SAlloc>& s, |
(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. The detailed match result is stored in m (if present).
[first, last).
|
If |
(until C++23) |
|
If |
(since C++23) |
[str, str + std::char_traits<CharT>::length(str)).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[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 |
| ||
| m[n].second |
| ||
| m[n].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) |
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) |