How to extract strings from a c++ string using regex

Question

I'm using regex by using #include <regex.h> If I have a string s, how can I use regex to search for a pattern p?

Which regex.h? The Unix one? You should better specify that, since it's not a standard C++ or C header. — Boaz Yaniv
– Boaz Yaniv, Commented May 4, 2011 at 0:43
I'm just using the one that's already there, so the default, whatever that is. I'm in OSX, which is basically the same as Linux. — neuromancer
– neuromancer, Commented May 4, 2011 at 0:50
What is your compiler and OS? Anyway, if you want cross-platform and cross-compiler compatibility and a good OO interface, I suggest trying Boost.Regex. boost.org/doc/libs/1_46_1/libs/regex/doc/html/index.html — Boaz Yaniv
– Boaz Yaniv, Commented May 4, 2011 at 0:51
You have two very different regular expression libraries available to you. #include <regex.h> is the C library, standardized by POSIX.1-2001. #include <regex> is the C++ library standardized in C++ TR1. You will probably find the C++ regular expression library more useful. — Robᵩ
– Robᵩ, Commented May 4, 2011 at 2:30

Robᵩ · Accepted Answer · 2011-05-04 02:24:54Z

4

#include <regex.h>
#include <iostream>
#include <string>

std::string
match(const char *string, char *pattern)
{

// Adapted from:
   http://pubs.opengroup.org/onlinepubs/009695399/functions/regcomp.html

    int    status;
    regex_t    re;
    regmatch_t rm;


    if (regcomp(&re, pattern, REG_EXTENDED) != 0) {
        return "Bad pattern";
    }
    status = regexec(&re, string, 1, &rm, 0);
    regfree(&re);
    if (status != 0) {
        return "No Match";
    }
    return std::string(string+rm.rm_so, string+rm.rm_eo);
}

int main(int ac, char **av) {
    // e.g. usage: ./program abcdefg 'c.*f'
    std::cout << match(av[1], av[2]) << "\n";
}

answered May 4, 2011 at 2:24

Robᵩ

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Comments

Suresh · Accepted Answer · 2011-05-04 00:59:32Z

1

Check http://msdn.microsoft.com/en-us/library/bb982821.aspx, has detailed usage patter for regex. from MS vc blog.

      const regex r("[1-9]\\d*x[1-9]\\d*");

      for (string s; getline(cin, s); ) {
               cout << (regex_match(s, r) ? "Yes" : "No") << endl;
      }

answered May 4, 2011 at 0:59

Suresh

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1 Comment

Robᵩ Over a year ago

That details the usage of <regex>. The OP asked for an example of <regex.h>. They are not the same API.

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