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# std::regex_search

From cppreference.com
< cpp‎ | regex

Defined in header `<regex>` |  |
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)
template< class Alloc, class CharT, class Traits > bool regex_search( const CharT* str, 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 ); | (2) | (since C++11)
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)
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)
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)
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)
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.

### [edit] 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`.

### [edit] 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 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 sub-expression n, or `last` if the subexpression did not participate in the match
m[n].second | the end of the sequence that matched 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

### [edit] Example

Run this code

    #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::ssub_match sub_match = color_match[i];
                std::string sub_match_str = sub_match.str();
                std::cout << i << ": " << sub_match_str << '\n';
            }
        }
    }

Output:

    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'

### [edit] See also

basic_regex (C++11) | regular expression object (class template) [edit]
match_results (C++11) | identifies one regular expression match, including all sub-expression matches (class template) [edit]
regex_match (C++11) | attempts to match a regular expression to an entire character sequence (function template) [edit]

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