std::regex_search
| Defined in header <regex>
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||
| template< class BidirIt, class Alloc, class CharT, class Traits > |
(1) | (since C++11) |
| template< class CharT, class Alloc, class Traits > bool regex_search( const CharT* str, |
(2) | (since C++11) |
| template< class STraits, class SAlloc, class Alloc, class CharT, class Traits > |
(3) | (since C++11) |
| template< class BidirIt, class CharT, class Traits > |
(4) | (since C++11) |
| template< class CharT, class Traits > bool regex_search( 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 there is a match between the regular expression e and some subsequence in the target character sequence.
[first, last). Match results are returned in m.match_results m with string iterators that become invalid immediately.regex_search will successfully match any subsequence of the given sequence, whereas std::regex_match will only return true if the regular expression matches the entire sequence.
Parameters
| first, last | - | a range identifying the target character sequence |
| str | - | a pointer to a null-terminated target character sequence |
| s | - | a string identifying target character sequence |
| e | - | the std::regex that should be applied to the target character sequence |
| m | - | the match results |
| flags | - | std::regex_constants::match_flag_type governing search behavior |
| Type requirements | ||
-BidirIt must meet the requirements of LegacyBidirectionalIterator.
| ||
-Alloc must meet the requirements of Allocator.
| ||
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 | m[0].first |
| m.prefix().matched | m.prefix().first != m.prefix().second |
| m.suffix().first | m[0].second |
| m.suffix().second | last |
| m.suffix().matched | m.suffix().first != m.suffix().second |
| m[0].first | the start of the matching sequence |
| m[0].second | the end of the matching sequence |
| m[0].matched | true |
| 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
In order to examine all matches within the target sequence, std::regex_search may be called in a loop, restarting each time from m[0].second of the previous call. std::regex_iterator offers an easy interface to this iteration.
Example
#include <cstddef> #include <iostream> #include <regex> #include <string> int main() { std::string lines[] = {"Roses are #ff0000", "violets are #0000ff", "all of my base are belong to you"}; std::regex color_regex("#([a-f0-9]{2})" "([a-f0-9]{2})" "([a-f0-9]{2})"); // simple match for (const auto& line : lines) std::cout << line << ": " << std::boolalpha << std::regex_search(line, color_regex) << '\n'; std::cout << '\n'; // show contents of marked subexpressions within each match std::smatch color_match; for (const auto& line : lines) if (std::regex_search(line, color_match, color_regex)) { std::cout << "matches for '" << line << "'\n"; std::cout << "Prefix: '" << color_match.prefix() << "'\n"; for (std::size_t i = 0; i < color_match.size(); ++i) std::cout << i << ": " << color_match[i] << '\n'; std::cout << "Suffix: '" << color_match.suffix() << "\'\n\n"; } // repeated search (see also std::regex_iterator) std::string log(R"( Speed: 366 Mass: 35 Speed: 378 Mass: 32 Speed: 400 Mass: 30)"); std::regex r(R"(Speed:\t\d*)"); for (std::smatch sm; regex_search(log, sm, r);) { std::cout << sm.str() << '\n'; log = sm.suffix(); } // C-style string demo std::cmatch cm; if (std::regex_search("this is a test", cm, std::regex("test"))) std::cout << "\nFound " << cm[0] << " at position " << cm.prefix().length() << '\n'; }
Output:
Roses are #ff0000: true violets are #0000ff: true all of my base are belong to you: false matches for 'Roses are #ff0000' Prefix: 'Roses are ' 0: #ff0000 1: ff 2: 00 3: 00 Suffix: '' matches for 'violets are #0000ff' Prefix: 'violets are ' 0: #0000ff 1: 00 2: 00 3: ff Suffix: '' Speed: 366 Speed: 378 Speed: 400 Found test at position 10
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 an entire character sequence (function template) |