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copied!<p>There are quite a lot of regular expression packages, but yours seems to match the one in POSIX: <a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/regcomp.html" rel="noreferrer"><code>regcomp()</code></a> etc.</p> <p>The two structures it defines in <code><regex.h></code> are:</p> <ul> <li><p><code>regex_t</code> containing at least <code>size_t re_nsub</code>, the number of parenthesized subexpressions.</p></li> <li><p><code>regmatch_t</code> containing at least <code>regoff_t rm_so</code>, the byte offset from start of string to start of substring, and <code>regoff_t rm_eo</code>, the byte offset from start of string of the first character after the end of substring.</p></li> </ul> <p>Note that 'offsets' are not pointers but indexes into the character array.</p> <p>The execution function is:</p> <ul> <li><code>int regexec(const regex_t *restrict preg, const char *restrict string, size_t nmatch, regmatch_t pmatch[restrict], int eflags);</code></li> </ul> <p>Your printing code should be:</p> <pre><code>for (int i = 0; i < r.re_nsub; i++) { int start = m[i].rm_so; int finish = m[i].rm_eo; strcpy(matches[ind], ("%.*s\n", (finish - start), p + start)); printf("Storing: %.*s\n", (finish - start), matches[ind]); ind++; printf("%.*s\n", (finish - start), p + start); } </code></pre> <p>Note that this code should be upgraded to ensure that the string copy does not overflow the target string. It is also a good idea to mark the start and end of a string, for example like:</p> <pre><code> printf("<<%.*s>>\n", (finish - start), p + start); </code></pre> <p>This makes it a whole heap easier to see spaces etc.</p> <p><em>[In future, please attempt to provide an SSCCE (<a href="http://sscce.org/" rel="noreferrer">Short, Self-Contained, Correct Example</a>) so that people can help more easily.]</em></p> <p>This is an SSCCE that I created, probably in response to another SO question in 2010. It is one of a number of programs I keep that I call 'vignettes'; little programs that show the essence of some feature (such as POSIX regexes, in this case). I find them useful as memory joggers.</p> <pre><code>#include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <regex.h> #define tofind "^DAEMONS=\\(([^)]*)\\)[ \t]*$" int main(int argc, char **argv) { FILE *fp; char line[1024]; int retval = 0; regex_t re; regmatch_t rm[2]; //this file has this line "DAEMONS=(sysklogd network sshd !netfs !crond)" const char *filename = "/etc/rc.conf"; if (argc > 1) filename = argv[1]; if (regcomp(&re, tofind, REG_EXTENDED) != 0) { fprintf(stderr, "Failed to compile regex '%s'\n", tofind); return EXIT_FAILURE; } fp = fopen(filename, "r"); if (fp == 0) { fprintf(stderr, "Failed to open file %s (%d: %s)\n", filename, errno, strerror(errno)); return EXIT_FAILURE; } while ((fgets(line, 1024, fp)) != NULL) { line[strlen(line)-1] = '\0'; if ((retval = regexec(&re, line, 2, rm, 0)) == 0) { printf("<<%s>>\n", line); printf("Line: <<%.*s>>\n", (int)(rm[0].rm_eo - rm[0].rm_so), line + rm[0].rm_so); printf("Text: <<%.*s>>\n", (int)(rm[1].rm_eo - rm[1].rm_so), line + rm[1].rm_so); char *src = line + rm[1].rm_so; char *end = line + rm[1].rm_eo; while (src < end) { size_t len = strcspn(src, " "); if (src + len > end) len = end - src; printf("Name: <<%.*s>>\n", (int)len, src); src += len; src += strspn(src, " "); } } } return EXIT_SUCCESS; } </code></pre> <p>This was designed to find a particular line starting <code>DAEMONS=</code> in a file <code>/etc/rc.conf</code>. You can adapt it to your purposes easily enough.</p>

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