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std::regex_search

Defined in header <regex>
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template< class BidirIt,
          class Alloc, class CharT, class Traits >
bool regex_search( 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)
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template< class CharT, class Alloc, class Traits >
bool regex_search( 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 );
 (2) (since C++11)
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template< class STraits, class SAlloc,
          class Alloc, class CharT, class Traits >
bool regex_search( 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 );
 (3) (since C++11)
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template< class BidirIt,
          class CharT, class Traits >
bool regex_search( BidirIt first, BidirIt last,
                   const std::basic_regex<CharT,Traits>& e,
                   std::regex_constants::match_flag_type flags =
                       std::regex_constants::match_default );
 (4) (since C++11)
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template< class CharT, class Traits >
bool regex_search( const CharT* str,
                   const std::basic_regex<CharT,Traits>& e,
                   std::regex_constants::match_flag_type flags =
                       std::regex_constants::match_default );
 (5) (since C++11)
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template< class STraits, class SAlloc,
          class CharT, class Traits >
bool regex_search( 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)
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template< class STraits, class SAlloc,
          class Alloc, class CharT, class Traits >
bool regex_search( 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++14)

Determines if there is a match between the regular expression e and some subsequence in the target character sequence.

1) Analyzes generic range [first,last). Match results are returned in m.
2) Analyzes a null-terminated string pointed to by str. Match results are returned in m.
3) Analyzes a string s. Match results are returned in m.
4-6) Equivalent to (1-3), just omits the match results.
7) The overload 3 is prohibited from accepting temporary strings, otherwise this function populates 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 BidirectionalIterator.
- 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

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#include <iostream>
#include <string>
#include <regex>
  
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})");
  
    for (const auto &line : lines) {
        std::cout << line << ": "
                  << std::regex_search(line, color_regex) << '\n';
    }  
  
    std::smatch color_match;
    for (const auto &line : lines) {
        std::regex_search(line, color_match, color_regex);
        std::cout << "matches for '" << line << "'\n";
        for (size_t i = 0; i < color_match.size(); ++i)
            std::cout << i << ": " << color_match[i] << '\n';
    }  
}

Output:

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Roses are #ff0000: 1
violets are #0000ff: 1
all of my base are belong to you: 0
matches for 'Roses are #ff0000'
0: #ff0000
1: ff
2: 00
3: 00
matches for 'violets are #0000ff'
0: #0000ff
1: 00
2: 00
3: ff
matches for 'all of my base are belong to you'

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)
doc_CPP
doc_CPP
2025-01-10 15:47:30
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