Regex in C

Regex in C
Replace using POSIX regular expressions

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

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

int rmatch(const char *string, char *pattern) {
  int status;
  regex_t re;
  if (regcomp(&re, pattern, REG_EXTENDED | REG_NOSUB) != 0) {
    return 0;
  }
  status = regexec(&re, string, (size_t) 0, NULL, 0);
  regfree(&re);
  if (status != 0) {
    return 0;
  }
  return 1;
}

int __rreplace(char *buf, int size, regex_t *re, char *rp) {
  char *pos;
  int sub, so, n;
  regmatch_t pmatch[10]; /* regoff_t is int so size is int */
  if (regexec(re, buf, 10, pmatch, 0))
    return 0;
  for (pos = rp; *pos; pos++)
    if (*pos == '\\' && *(pos + 1) > '0' && *(pos + 1) <= '9') {
      so = pmatch[*(pos + 1) - 48].rm_so;
      n = pmatch[*(pos + 1) - 48].rm_eo - so;
      if (so < 0 || strlen(rp) + n - 1 > size)
        return 1;
      memmove(pos + n, pos + 2, strlen(pos) - 1);
      memmove(pos, buf + so, n);
      pos = pos + n - 2;
    }
  sub = pmatch[1].rm_so; /* no repeated replace when sub >= 0 */
  for (pos = buf; !regexec(re, pos, 1, pmatch, 0);) {
    n = pmatch[0].rm_eo - pmatch[0].rm_so;
    pos += pmatch[0].rm_so;
    if (strlen(buf) - n + strlen(rp) + 1 > size)
      return 1;
    memmove(pos + strlen(rp), pos + n, strlen(pos) - n + 1);
    memmove(pos, rp, strlen(rp));
    pos += strlen(rp);
    if (sub >= 0)
      break;
  }
  return 0;
}

int rreplace(char *buf, int size, char *expressions, char *rp) {
  int result;
  regex_t re;
  regcomp (&re, expressions, REG_ICASE);
  result = __rreplace(buf, size, &re, rp);
  regfree (&re);
  return result;
}

int main(void) {
  // match
  printf("%s\r\n", rmatch("Hello World!", "^Hello.*!$") == 1 ? "true":"false");

  // replace
  int buf_size = 4096;
  char buf [buf_size];

  strcpy(buf, "hello world!");
  rreplace(buf, buf_size, "world", "Jack");
  printf("%s\r\n", buf);

  return EXIT_SUCCESS;
}