Its not a script, it is a single function called match() You pass match two arguments - one is the string you want to check, the other the regex patern you want that string to match. The regex pattern is shown in the Perl example. The function returns 1 if it matches. I don't know how it could be simpler.

[root@devel3 root]# cat test.c
#include <stdio.h>
#include <regex.h>

int
main(int argc, char *argv[])
{
  int i;
  char *pat = "^[A-Z]+$";
  printf("Got %d args\n", argc-1 ); /* first arg prog name */
  for( i=1; i<argc; i++ ) {
      printf("Got %s\n",argv[i]);
      if ( match( argv[i], pat ) ) {
          printf("-->Match %s\n", pat);
      }
      else {
          printf("***Fail\n");
      }
  }
  return 0;
}

int
match(const char *string, char *pattern)
{
    int    status;
    regex_t    re;

    if (regcomp(&re, pattern, REG_EXTENDED|REG_NOSUB) != 0) {
        return(0);      /* report error */
    }
    status = regexec(&re, string, (size_t) 0, NULL, 0);
    regfree(&re);
    if (status != 0) {
        return(0);      /* report error */
    }
    return(1);
}

[root@devel3 root]# gcc test.c
[root@devel3 root]# ./a.out 123 ABC abc ABC123
Got 4 args
Got 123
***Fail
Got ABC
-->Match ^[A-Z]+$
Got abc
***Fail
Got ABC123
***Fail
[root@devel3 root]#
[download]

I have no comprehension why you want to do data validation in C before you call a Perl script. Surely the Perl does data validation????? If so just use your C wrapper to exec the Perl script. End of story.