std::regex_search

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 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 );	(2)	(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 );	(3)	(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 );	(4)	(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 );	(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++11)

Determines if there is a match between the regular expression e and some subsequence in the target character sequence. The detailed match result is stored in m (if present).

1,2) The target character sequence is represented by the range [first, last).

If `BidirIt` does not satisfy the requirements of LegacyBidirectionalIterator, the behavior is undefined.	(until C++23)
If `BidirIt` does not model `bidirectional_iterator`, the behavior is undefined.	(since C++23)

3,4) The target character sequence is represented by the range [str, str + std::char_traits<CharT>::length(str)).

5,6) The target character sequence is represented by the string s.

7) The target character sequence cannot be represented by a std::string rvalue.

If a 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 a 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
Expression	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[0].first`
`m.prefix().matched`	`m.prefix().first != m.prefix().second`
`m.suffix().first`	`m[0].second`
`m.suffix().second`	`last`	`std::char_traits<CharT>::length(str) + str`	`s.end()`
`m.suffix().matched`	`m.suffix().first != m.suffix().second`
`m[0].first`	the start of the sequence that matched `e`
`m[0].second`	the end of the sequence that matched `e`
`m[0].matched`	`true`
`m[n].first`	`last` if marked sub-expression `n` did not participate in the match the start of the sequence otherwise matching sub-expression `n` otherwise
`m[n].second`	`last` if marked sub-expression `n` did not participate in the match the end of the sequence otherwise matching sub-expression `n` otherwise
`m[n].matched`	`false` if marked sub-expression `n` did not participate in the match `true` otherwise

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 a match exists, 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 2205	C++11	`n` could be zero in the postcondition	can only be positive
LWG 2329	C++11	overload (5) accepted `basic_string` rvalues, which could result in dangling iterators	rejected via deleted overload (7)