std::regex_search

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Regular expressions library

Classes

basic_regex (C++11)

sub_match (C++11)

match_results (C++11)

Algorithms

regex_match (C++11)

regex_search (C++11)

regex_replace (C++11)

Iterators

regex_iterator (C++11)

regex_token_iterator (C++11)

Exceptions

regex_error (C++11)

Traits

regex_traits (C++11)

Constants

syntax_option_type (C++11)

match_flag_type (C++11)

error_type (C++11)

Regex Grammar

Modified ECMAScript-262 (C++11)

 

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.

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

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

See also

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