std::regex_search

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< cpp‎ | regex
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Regular expressions library
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regex_search
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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

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

If BidirIt does not satisfy the requirements of LegacyBidirectionalIterator

(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

Expression       Value
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
  • the start of the sequence otherwise matching sub-expression n otherwise
m [n] .second
m [n] .matched

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

Example

Run this code
#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)

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)
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