Namespaces
Variants
Views
Actions

Difference between revisions of "cpp/regex/regex match"

From cppreference.com
< cpp‎ | regex
(const'ify)
(LWG2329)
Line 55: Line 55:
 
                       std::regex_constants::match_default );
 
                       std::regex_constants::match_default );
 
}}
 
}}
−
{{dcl | num=7 | since=c++14 | 1=
+
{{dcl | num=7 | since=c++11 | 1=
 
template< class STraits, class SAlloc,  
 
template< class STraits, class SAlloc,  
 
           class Alloc, class CharT, class Traits >
 
           class Alloc, class CharT, class Traits >
Line 73: Line 73:
 
@1@ Determines if there is a match between the regular expression {{tt|e}} and the entire target character sequence {{tt|[first,last)}}, taking into account the effect of {{tt|flags}}. When determining if there is a match, only potential matches that match the entire character sequence are considered. Match results are returned in {{tt|m}}.
 
@1@ Determines if there is a match between the regular expression {{tt|e}} and the entire target character sequence {{tt|[first,last)}}, taking into account the effect of {{tt|flags}}. When determining if there is a match, only potential matches that match the entire character sequence are considered. Match results are returned in {{tt|m}}.
  
−
@2@ Behaves as (1) above, omitting the match results.
+
@2@ Behaves as {{v|1}} above, omitting the match results.
  
 
@3@ Returns {{c|std::regex_match(str, str + std::char_traits<charT>::length(str), m, e, flags)}}.
 
@3@ Returns {{c|std::regex_match(str, str + std::char_traits<charT>::length(str), m, e, flags)}}.
Line 83: Line 83:
 
@6@ Returns {{c|std::regex_match(s.begin(), s.end(), e, flags)}}.
 
@6@ Returns {{c|std::regex_match(s.begin(), s.end(), e, flags)}}.
  
−
@7@ The overload 4 is prohibited from accepting temporary strings, otherwise this function populates match_results m with string iterators that become invalid immediately.
+
@7@ The overload {{v|4}} is prohibited from accepting temporary strings, otherwise this function populates {{tt|match_results}} {{tt|m}} with string iterators that become invalid immediately.
  
 
Note that {{tt|regex_match}} will only successfully match a regular expression to an ''entire'' character sequence, whereas {{lc|std::regex_search}} will successfully match subsequences.
 
Note that {{tt|regex_match}} will only successfully match a regular expression to an ''entire'' character sequence, whereas {{lc|std::regex_search}} will successfully match subsequences.
Line 207: Line 207:
 
   submatch 2: dat
 
   submatch 2: dat
 
}}
 
}}
 +
 +
===Defect reports===
 +
{{dr list begin}}
 +
{{dr list item|wg=lwg|dr=2329|std=C++11|before={{tt|basic_string}} rvalues were accepted, which was likely to result in dangling iterators|after=rejected via a deleted overload}}
 +
{{dr list end}}
  
 
===See also===
 
===See also===
Line 215: Line 220:
 
{{dsc end}}
 
{{dsc end}}
  
−
[[de:cpp/regex/regex match]]
+
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}
−
[[es:cpp/regex/regex match]]
+
−
[[fr:cpp/regex/regex match]]
+
−
[[it:cpp/regex/regex match]]
+
−
[[ja:cpp/regex/regex match]]
+
−
[[pt:cpp/regex/regex match]]
+
−
[[ru:cpp/regex/regex match]]
+
−
[[zh:cpp/regex/regex match]]
+

Revision as of 22:00, 20 August 2020

 
C++
 
Regular expressions library
Classes
(C++11)
(C++11)
(C++11)
Algorithms
regex_match
(C++11)
(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_match( 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_match( 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_match( 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 STraits, class SAlloc,

          class Alloc, class CharT, class Traits >
bool regex_match( 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 );
 (4) (since C++11)
template< class CharT, class Traits >

bool regex_match( 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_match( 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_match( 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 the regular expression e matches the entire target character sequence, which may be specified as std::string, a C-string, or an iterator pair.

1) Determines if there is a match between the regular expression e and the entire target character sequence [first,last), taking into account the effect of flags. When determining if there is a match, only potential matches that match the entire character sequence are considered. Match results are returned in m.
2) Behaves as (1) above, omitting the match results.
3) Returns std::regex_match(str, str + std::char_traits<charT>::length(str), m, e, flags).
4) Returns std::regex_match(s.begin(), s.end(), m, e, flags).
5) Returns std::regex_match(str, str + std::char_traits<charT>::length(str), e, flags).
6) Returns std::regex_match(s.begin(), s.end(), e, flags).
7) The overload (4) is prohibited from accepting temporary strings, otherwise this function populates match_results m with string iterators that become invalid immediately.

Note that regex_match will only successfully match a regular expression to an entire character sequence, whereas std::regex_search will successfully match subsequences.

Contents

Parameters

first, last - the target character range to apply the regex to, given as iterators
m - the match results
str - the target string, given as a null-terminated C-style string
s - the target string, given as a std::basic_string
e - the regular expression
flags - flags used to determine how the match will be performed
Type requirements
-
BidirIt must meet the requirements of LegacyBidirectionalIterator.

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 first
m.prefix().matched false (the match prefix is empty)
m.suffix().first last
m.suffix().second last
m.suffix().matched false (the match suffix is empty)
m[0].first first
m[0].second last
m[0].matched true (the entire sequence is matched)
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

Because regex_match only considers full matches, the same regex may give different matches between regex_match and std::regex_search: 

std::regex re("Get|GetValue");
std::cmatch m;
std::regex_search("GetValue", m, re);  // returns true, and m[0] contains "Get"
std::regex_match ("GetValue", m, re);  // returns true, and m[0] contains "GetValue"
std::regex_search("GetValues", m, re); // returns true, and m[0] contains "Get"
std::regex_match ("GetValues", m, re); // returns false

Example

Run this code
#include <iostream>
#include <string>
#include <regex>
 
int main()
{
    // Simple regular expression matching
    const std::string fnames[] = {"foo.txt", "bar.txt", "baz.dat", "zoidberg"};
    const std::regex txt_regex("[a-z]+\\.txt");
 
    for (const auto &fname : fnames) {
        std::cout << fname << ": " << std::regex_match(fname, txt_regex) << '\n';
    }   
 
    // Extraction of a sub-match
    const std::regex base_regex("([a-z]+)\\.txt");
    std::smatch base_match;
 
    for (const auto &fname : fnames) {
        if (std::regex_match(fname, base_match, base_regex)) {
            // The first sub_match is the whole string; the next
            // sub_match is the first parenthesized expression.
            if (base_match.size() == 2) {
                std::ssub_match base_sub_match = base_match[1];
                std::string base = base_sub_match.str();
                std::cout << fname << " has a base of " << base << '\n';
            }
        }
    }
 
    // Extraction of several sub-matches
    const std::regex pieces_regex("([a-z]+)\\.([a-z]+)");
    std::smatch pieces_match;
 
    for (const auto &fname : fnames) {
        if (std::regex_match(fname, pieces_match, pieces_regex)) {
            std::cout << fname << '\n';
            for (size_t i = 0; i < pieces_match.size(); ++i) {
                std::ssub_match sub_match = pieces_match[i];
                std::string piece = sub_match.str();
                std::cout << "  submatch " << i << ": " << piece << '\n';
            }   
        }   
    }   
}

Output: 

foo.txt: 1
bar.txt: 1
baz.dat: 0
zoidberg: 0
foo.txt has a base of foo
bar.txt has a base of bar
foo.txt
  submatch 0: foo.txt
  submatch 1: foo
  submatch 2: txt
bar.txt
  submatch 0: bar.txt
  submatch 1: bar
  submatch 2: txt
baz.dat
  submatch 0: baz.dat
  submatch 1: baz
  submatch 2: dat

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

See also

(C++11)
 regular expression object
(class template) [edit]
(C++11)
 identifies one regular expression match, including all sub-expression matches
(class template) [edit]
(C++11)
 attempts to match a regular expression to any part of a character sequence
(function template) [edit]
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/regex/regex_match&oldid=121910"