NAME¶

std::regex_search - std::regex_search

Synopsis¶

Defined in header <regex>
template< class BidirIt,

class Alloc, class CharT, class Traits >
bool regex_search( BidirIt first, BidirIt last, (since
std::match_results<BidirIt,Alloc>& m, (1) C++11)
const std::basic_regex<CharT,Traits>& e,
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
template< class CharT, class Alloc, class Traits >

bool regex_search( const CharT* str,
std::match_results<const CharT*,Alloc>& m, (2) (since
const std::basic_regex<CharT,Traits>& e, C++11)
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
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 (since
std::basic_string<CharT,STraits,SAlloc>::const_iterator, (3) C++11)
Alloc
>& m,
const std::basic_regex<CharT, Traits>& e,
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
template< class BidirIt,

class CharT, class Traits >
bool regex_search( BidirIt first, BidirIt last, (4) (since
const std::basic_regex<CharT,Traits>& e, C++11)
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
template< class CharT, class Traits >

bool regex_search( const CharT* str, (since
const std::basic_regex<CharT,Traits>& e, (5) C++11)
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
template< class STraits, class SAlloc,

class CharT, class Traits >
bool regex_search( const std::basic_string<CharT,STraits,SAlloc>& s, (6) (since
const std::basic_regex<CharT,Traits>& e, C++11)
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default );
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 (since
std::basic_string<CharT,STraits,SAlloc>::const_iterator, (7) C++11)
Alloc
>&,
const std::basic_regex<CharT, Traits>&,
std::regex_constants::match_flag_type flags =

std::regex_constants::match_default ) = delete;

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 <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
basic_string rvalues were accepted, which rejected via a deleted
LWG 2329 C++11 was likely to result in dangling overload
iterators

See also¶

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