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

Revision as of 16:59, 23 January 2023

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.

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

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basic_regex (C++11)	regular expression object (class template) [edit]
match_results (C++11)	identifies one regular expression match, including all sub-expression matches (class template) [edit]
regex_search (C++11)	attempts to match a regular expression to any part of a character sequence (function template) [edit]

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

Revision as of 16:59, 23 January 2023

Contents

Parameters

Return value

Notes

Example

Defect reports

See also

Navigation

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@@ Line 2: / Line 2: @@
 {{cpp/regex/navbar}}
 {{dcl begin}}
-{{dcl header | regex}}
+{{dcl header|regex}}
-{{dcl | num=1 | since=c++11 | 1=
+{{dcl|num=1|since=c++11|1=
 template< class BidirIt,
            class Alloc, class CharT, class Traits >
 bool regex_match( BidirIt first, BidirIt last,
-                   std::match_results<BidirIt,Alloc>& m,
+                   std::match_results<BidirIt, Alloc>& m,
-                   const std::basic_regex<CharT,Traits>& e,
+                   const std::basic_regex<CharT, Traits>& e,
                    std::regex_constants::match_flag_type flags =
                        std::regex_constants::match_default );
 }}
-{{dcl | num=2 | since=c++11 | 1=
+{{dcl|num=2|since=c++11|1=
 template< class BidirIt,
            class CharT, class Traits >
 bool regex_match( BidirIt first, BidirIt last,
-                   const std::basic_regex<CharT,Traits>& e,
+                   const std::basic_regex<CharT, Traits>& e,
                    std::regex_constants::match_flag_type flags =
                        std::regex_constants::match_default );
 }}
-{{dcl | num=3 | since=c++11 | 1=
+{{dcl|num=3|since=c++11|1=
 template< class CharT, class Alloc, class Traits >
 bool regex_match( const CharT* str,
-                   std::match_results<const CharT*,Alloc>& m,
+                   std::match_results<const CharT*, Alloc>& m,
-                   const std::basic_regex<CharT,Traits>& e,
+                   const std::basic_regex<CharT, Traits>& e,
                    std::regex_constants::match_flag_type flags =
                        std::regex_constants::match_default );
 }}
-{{dcl | num=4 | since=c++11 | 1=
+{{dcl|num=4|since=c++11|1=
 template< class STraits, class SAlloc,
            class Alloc, class CharT, class Traits >
-bool regex_match( const std::basic_string<CharT,STraits,SAlloc>& s,
+bool regex_match( const std::basic_string<CharT, STraits, SAlloc>& s,
                    std::match_results<
-                       typename std::basic_string<CharT,STraits,SAlloc>::const_iterator,
+                       typename std::basic_string<CharT, STraits, SAlloc>::
-                       Alloc
+                          const_iterator,
-                  >& m,
+                       Alloc>& m,
-                   const std::basic_regex<CharT,Traits>& e,
+                   const std::basic_regex<CharT, Traits>& e,
                    std::regex_constants::match_flag_type flags =
                        std::regex_constants::match_default );
 }}
-{{dcl | num=5 | since=c++11 | 1=
+{{dcl|num=5|since=c++11|1=
 template< class CharT, class Traits >
 bool regex_match( const CharT* str,
-                   const std::basic_regex<CharT,Traits>& e,
+                   const std::basic_regex<CharT, Traits>& e,
                    std::regex_constants::match_flag_type flags =
                        std::regex_constants::match_default );
 }}
-{{dcl | num=6 | since=c++11 | 1=
+{{dcl|num=6|since=c++11|1=
 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,
+                   const std::basic_regex<CharT, Traits>& e,
                    std::regex_constants::match_flag_type flags =
                        std::regex_constants::match_default );
 }}
-{{dcl | num=7 | since=c++11 | 1=
+{{dcl|num=7|since=c++11|1=
 template< class STraits, class SAlloc,
            class Alloc, class CharT, class Traits >
-bool regex_match( const std::basic_string<CharT,STraits,SAlloc>&&,
+bool regex_match( const std::basic_string<CharT, STraits, SAlloc>&&,
                    std::match_results<
-                       typename std::basic_string<CharT,STraits,SAlloc>::const_iterator,
+                       typename std::basic_string<CharT, STraits, SAlloc>::
-                       Alloc
+                          const_iterator,
-                  >&,
+                       Alloc>&,
-                   const std::basic_regex<CharT,Traits>&,
+                   const std::basic_regex<CharT, Traits>&,
                    std::regex_constants::match_flag_type flags =
                        std::regex_constants::match_default ) = delete;
 }}
@@ Line 75: / Line 75: @@
 @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)}}.
 @4@ Returns {{c|std::regex_match(s.begin(), s.end(), m, e, flags)}}.
-@5@ Returns {{c|std::regex_match(str, str + std::char_traits<charT>::length(str), e, flags)}}.
+@5@ Returns {{c|std::regex_match(str, str + std::char_traits<CharT>::length(str), e, flags)}}.
 @6@ Returns {{c|std::regex_match(s.begin(), s.end(), e, flags)}}.
@@ Line 89: / Line 89: @@
 ===Parameters===
 {{par begin}}
-{{par | first, last | the target character range to apply the regex to, given as iterators}}
+{{par|first, last|the target character range to apply the regex to, given as iterators}}
-{{par | m | the match results}}
+{{par|m|the match results}}
-{{par | str | the target string, given as a null-terminated C-style string}}
+{{par|str|the target string, given as a null-terminated C-style string}}
-{{par | s | the target string, given as a {{lc|std::basic_string}} }}
+{{par|s|the target string, given as a {{lc|std::basic_string}}}}
-{{par | e | the regular expression}}
+{{par|e|the regular expression}}
-{{par | flags | flags used to determine how the match will be performed}}
+{{par|flags|flags used to determine how the match will be performed}}
 {{par hreq}}
-{{par req named | BidirIt | BidirectionalIterator}}
+{{par req named|BidirIt|BidirectionalIterator}}
 {{par end}}
@@ Line 104: / Line 104: @@
 If the match does not exist:
 {{dsc begin}}
-{{dsc | {{c|1=m.ready() == true}} }}
+{{dsc|{{c|1=m.ready() == true}}}}
-{{dsc | {{c|1=m.empty() == true}} }}
+{{dsc|{{c|1=m.empty() == true}}}}
-{{dsc | {{c|1=m.size() == 0}} }}
+{{dsc|{{c|1=m.size() == 0}}}}
 {{dsc end}}
 If the match exists:
 {{dsc begin}}
-{{dsc | {{c|m.ready()}} | {{c|true}} }}
+{{dsc|{{c|m.ready()}}|{{c|true}}}}
-{{dsc | {{c|m.empty()}} | {{c|false}} }}
+{{dsc|{{c|m.empty()}}|{{c|false}}}}
-{{dsc | {{c|m.size()}}  | [[cpp/regex/ecmascript#Sub-expressions|number of marked subexpressions]] plus 1, that is, {{c|1+e.mark_count()}}}}
+{{dsc|{{c|m.size()}}|[[cpp/regex/ecmascript#Sub-expressions|number of marked subexpressions]] plus 1, that is, {{c|1+e.mark_count()}}}}
-{{dsc | {{c|m.prefix().first}} | {{tt|first}} }}
+{{dsc|{{c|m.prefix().first}}|{{tt|first}}}}
-{{dsc | {{c|m.prefix().second}} | {{tt|first}} }}
+{{dsc|{{c|m.prefix().second}}|{{tt|first}}}}
-{{dsc | {{c|m.prefix().matched}} | {{c|false}} (the match prefix is empty) }}
+{{dsc|{{c|m.prefix().matched}}|{{c|false}} (the match prefix is empty) }}
-{{dsc | {{c|m.suffix().first}} | {{tt|last}}}}
+{{dsc|{{c|m.suffix().first}}|{{tt|last}}}}
-{{dsc | {{c|m.suffix().second}} | {{tt|last}}}}
+{{dsc|{{c|m.suffix().second}}|{{tt|last}}}}
-{{dsc | {{c|m.suffix().matched}} | {{c|false}} (the match suffix is empty) }}
+{{dsc|{{c|m.suffix().matched}}|{{c|false}} (the match suffix is empty) }}
-{{dsc | {{c|m[0].first}} | {{tt|first}} }}
+{{dsc|{{c|m[0].first}}|{{tt|first}}}}
-{{dsc | {{c|m[0].second}} | {{tt|last}} }}
+{{dsc|{{c|m[0].second}}|{{tt|last}}}}
-{{dsc | {{c|m[0].matched}} | {{c|true}} (the entire sequence is matched)}}
+{{dsc|{{c|m[0].matched}}|{{c|true}} (the entire sequence is matched)}}
-{{dsc | {{c|1=m[n].first}} | the start of the sequence that matched [[cpp/regex/ecmascript#Sub-expressions|marked sub-expression]] n, or {{tt|last}} if the subexpression did not participate in the match}}
+{{dsc|{{c|1=m[n].first}}|the start of the sequence that matched [[cpp/regex/ecmascript#Sub-expressions|marked sub-expression]] n, or {{tt|last}} if the subexpression did not participate in the match}}
-{{dsc | {{c|1=m[n].second}} | the end of the sequence that matched [[cpp/regex/ecmascript#Sub-expressions|marked sub-expression]] n, or {{tt|last}} if the subexpression did not participate in the match}}
+{{dsc|{{c|1=m[n].second}}|the end of the sequence that matched [[cpp/regex/ecmascript#Sub-expressions|marked sub-expression]] n, or {{tt|last}} if the subexpression did not participate in the match}}
-{{dsc | {{c|1=m[n].matched}} | {{c|true}} if sub-expression n participated in the match, {{c|false}} otherwise}}
+{{dsc|{{c|1=m[n].matched}}|{{c|true}} if sub-expression n participated in the match, {{c|false}} otherwise}}
 {{dsc end}}
@@ Line 141: / Line 141: @@
 ===Example===
 {{example
- | code=
+|code=
 #include <iostream>
 #include <string>
@@ Line 152: / Line 152: @@
      const std::regex txt_regex("[a-z]+\\.txt");
-     for (const auto &fname : fnames) {
+     for (const auto &fname : fnames)
          std::cout << fname << ": " << std::regex_match(fname, txt_regex) << '\n';
-    }
      // Extraction of a sub-match
@@ Line 160: / Line 159: @@
      std::smatch base_match;
-     for (const auto &fname : fnames) {
+     for (const auto &fname : fnames)
-         if (std::regex_match(fname, base_match, base_regex)) {
+    {
+         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) {
+             if (base_match.size() == 2)
+            {
                  std::ssub_match base_sub_match = base_match[1];
                  std::string base = base_sub_match.str();
@@ Line 176: / Line 178: @@
      std::smatch pieces_match;
-     for (const auto &fname : fnames) {
+     for (const auto &fname : fnames)
-         if (std::regex_match(fname, pieces_match, pieces_regex)) {
+    {
+         if (std::regex_match(fname, pieces_match, pieces_regex))
+        {
              std::cout << fname << '\n';
-             for (size_t i = 0; i < pieces_match.size(); ++i) {
+             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=
+|output=
 foo.txt: 1
 bar.txt: 1
@@ Line 215: / Line 220: @@
 ===See also===
 {{dsc begin}}
-{{dsc inc | cpp/regex/dsc basic_regex}}
+{{dsc inc|cpp/regex/dsc basic_regex}}
-{{dsc inc | cpp/regex/dsc match_results}}
+{{dsc inc|cpp/regex/dsc match_results}}
-{{dsc inc | cpp/regex/dsc regex_search}}
+{{dsc inc|cpp/regex/dsc regex_search}}
 {{dsc end}}
 {{langlinks|de|es|fr|it|ja|pt|ru|zh}}