C++ Regex_Match Not Working

C++ regex_match not working

The problem is that std::regex_match must match the entire string but you are trying to match only part of it.

You need to either use std::regex_search or alter your regular expression to match all three parts at once:

#include <regex>
#include <string>
#include <iostream>

const auto test =
{
      "foo.bar = 15"
    , "baz.asd = 13"
    , "ddd.dgh = 66"
};

int main()
{
    const std::regex r(R"~(([^.]+)\.([^\s]+)[^0-9]+(\d+))~");
    //                     (  1  )  (   2  )       ( 3 ) <- capture groups

    std::cmatch m;

    for(const auto& line: test)
    {
        if(std::regex_match(line, m, r))
        {
            // m.str(0) is the entire matched string
            // m.str(1) is the 1st capture group
            // etc...
            std::cout << "a = " << m.str(1) << '\n';
            std::cout << "b = " << m.str(2) << '\n';
            std::cout << "c = " << m.str(3) << '\n';
            std::cout << '\n';
        }
    }
}

Regular expression: https://regex101.com/r/kB2cX3/2

Output:

a = foo
b = bar
c = 15

a = baz
b = asd
c = 13

a = ddd
b = dgh
c = 66

Regex not working as expected with C++ regex_match

You need to use a regex_search rather than regex_match:

bool found = regex_search("<html>",regex("h.*l"));

See IDEONE demo

In plain words, regex_search will search for a substring at any position in the given string. regex_match will only return true if the entire input string is matched (same behavior as matches in Java).

The regex_match documentation says:

Returns whether the target sequence matches the regular expression rgx.

The entire target sequence must match the regular expression for this function >to return true (i.e., without any additional characters before or after the >match). For a function that returns true when the match is only part of the >sequence, see regex_search.

The regex_search is different:

Returns whether some sub-sequence in the target sequence (the subject) matches the regular expression rgx (the pattern).

Complicated regex_match not working in C++

Thanks to @MYGz I was able to fix this. Maybe it had something to do with escape characters.

All I did to change @MYGz's suggestion was to remove the \s.

It worked with ([0-1]?[0-2]:[0-5][0-9] *[AaPp][Mm])

Regex is not working in C

grep -E uses some enhanced ERE syntax meaning that the {n,m} quantifier braces (and also ( and )) do not have to be escaped (not the case in BRE regex).

You need to pass REG_EXTENDED flag to the regcomp, and also, since you can't use a word boundary, replace the first \b with (^|[^[:alnum:]_]) "equivalent". You need no trailing \b since there is a : in the pattern right after:

const char *str_regex = "(^|[^[:alnum:]_])(abc|def):[0-9]{10}@([A-Za-z0-9].*)";

The (^|[^[:alnum:]_]) part matches either the start of the string (^) or (|) a char other than alphanumeric or an underscore.

Full C demo:

#include <stdio.h>
#include <stdlib.h>
#include <regex.h>

int main (void)
{
  int match;
  int err;
  regex_t preg;
  regmatch_t pmatch[4];
  size_t nmatch = 4;
  const char *str_request = "abc:1234567890@werty.wer.sdfg.net";

  const char *str_regex = "(^|[^[:alnum:]_])(abc|def):[0-9]{10}@([A-Za-z0-9].*)";
  err = regcomp(&preg, str_regex, REG_EXTENDED);
  if (err == 0)
    {
      match = regexec(&preg, str_request, nmatch, pmatch, 0);
      nmatch = preg.re_nsub;
      regfree(&preg);
      if (match == 0)
        {
          printf("\"%.*s\"\n", pmatch[2].rm_eo - pmatch[2].rm_so, &str_request[pmatch[2].rm_so]);
          printf("\"%.*s\"\n", pmatch[3].rm_eo - pmatch[3].rm_so, &str_request[pmatch[3].rm_so]);
        }
      else if (match == REG_NOMATCH)
        {
          printf("unmatch\n");
        }
    }
  return 0;
 }

linux g++ regular expressions not working

you do not need '\' before ':'. so the correct line is:
std::regex re("SerialNumber: (.*)\n");
with this change your code works with gcc starting gcc 4.9.1. https://wandbox.org/permlink/uuVCxdtpHAjZTghP

Why doesn't std::regex_match return true with $ pattern?

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

You want regex_search for matching subsequences. $ does not match the entirety of a non-empty string, but does match a (zero-length) substring of a non-empty string.

C++ Regex_Match Not Working