std:: regex_search

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C++
Regular expressions library
Classes
(C++11)
(C++11)
(C++11)
Algorithms
(C++11)
regex_search
(C++11)
(C++11)
Iterators
(C++11)
(C++11)
Exceptions
(C++11)
Traits
(C++11)
Constants
(C++11)
(C++11)
(C++11)
Regex Grammar
(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 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
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

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

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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