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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 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)
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 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

### [edit] 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.

### [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})");

        // 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 (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*)");
        std::smatch sm;
        while(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();
    }

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

### [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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