std::regex_search (3) - Linux Manuals

std::regex_search: std::regex_search

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,
std::match_results<BidirIt,Alloc>& m, (1) (since 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 C++11)
const std::basic_regex<CharT,Traits>& e,
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 std::basic_string<CharT,STraits,SAlloc>::const_iterator, (3) (since 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 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 Traits >
bool regex_search( const CharT* str,
const std::basic_regex<CharT,Traits>& e, (5) (since 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 C++11)
const std::basic_regex<CharT,Traits>& e,
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 std::basic_string<CharT,STraits,SAlloc>::const_iterator, (7) (since C++14)
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 <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