std::regex_match
Defined in header <regex> |
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|---|---|---|
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(1) | (since C++11) |
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(2) | (since C++11) |
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(3) | (since C++11) |
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(4) | (since C++11) |
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(5) | (since C++11) |
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(6) | (since C++11) |
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(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.
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. |
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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 |
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m.empty() == true |
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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 falseExample
#include <cstddef>
#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 (std::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: datDefect 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
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(C++11)
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regular expression object (class template) |
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(C++11)
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identifies one regular expression match, including all sub-expression matches (class template) |
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(C++11)
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attempts to match a regular expression to any part of a character sequence (function template) |
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https://en.cppreference.com/w/cpp/regex/regex_match