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

Revision as of 09:46, 16 August 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 <regex>
#include <string>
 
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

@@ Line 69: / Line 69: @@
 {{dcl end}}
-Determines if the regular expression {{tt|e}} matches the entire target character sequence, which may be specified as {{lc|std::string}}, a C-string, or an iterator pair.
+Determines if the regular expression {{c|e}} matches the entire target character sequence, which may be specified as {{lc|std::string}}, a C-string, or an iterator pair.
-@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 {{c|e}} and the entire target character sequence {{range|first|last}}, taking into account the effect of {{c|flags}}. When determining if there is a match, only potential matches that match the entire character sequence are considered. Match results are returned in {{c|m}}.
 @2@ Behaves as {{v|1}} above, omitting the match results.
@@ Line 83: / Line 83: @@
 @6@ Returns {{c|std::regex_match(s.begin(), s.end(), e, flags)}}.
-@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.
+@7@ The overload {{v|4}} is prohibited from accepting temporary strings, otherwise this function populates {{tt|match_results}} {{c|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.
@@ Line 100: / Line 100: @@
 ===Return value===
-Returns {{c|true}} if a match exists, {{c|false}} otherwise. In either case, the object {{tt|m}} is updated, as follows:
+Returns {{c|true}} if a match exists, {{c|false}} otherwise. In either case, the object {{c|m}} is updated, as follows:
 If the match does not exist:
@@ Line 114: / Line 114: @@
 {{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.prefix().first}}|{{tt|first}}}}
+{{dsc|{{c|m.prefix().first}}|{{c|first}}}}
-{{dsc|{{c|m.prefix().second}}|{{tt|first}}}}
+{{dsc|{{c|m.prefix().second}}|{{c|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}}|{{c|last}}}}
-{{dsc|{{c|m.suffix().second}}|{{tt|last}}}}
+{{dsc|{{c|m.suffix().second}}|{{c|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}}|{{c|first}}}}
-{{dsc|{{c|m[0].second}}|{{tt|last}}}}
+{{dsc|{{c|m[0].second}}|{{c|last}}}}
 {{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 {{c|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 {{c|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 end}}

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Standard library
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Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (C++17)
Regular expressions library (C++11)
Concurrency support library (C++11)
Execution support library (C++26)
Technical specifications
Symbols index
External libraries

Classes
basic_regex (C++11)
sub_match (C++11)
match_results (C++11)
Algorithms
regex_match (C++11)
regex_search (C++11)
regex_replace (C++11)
Iterators
regex_iterator (C++11)
regex_token_iterator (C++11)
Exceptions
regex_error (C++11)
Traits
regex_traits (C++11)
Constants
syntax_option_type (C++11)
match_flag_type (C++11)
error_type (C++11)
Regex Grammar
Modified ECMAScript-262 (C++11)

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 09:46, 16 August 2023

Contents

Parameters

Return value

Notes

Example

Defect reports

See also

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