piece of code: try to reimplement 'strtok', 'strspn', 'strcspn' in Standard C Library.

gistfile1.c

/* find index of first s1[i] that matches any s2[]. */
size_t czf_strcspn(const char *s1, const char *s2) {
    const char *sc1, *sc2;
    for (sc1 = s1; *sc1 != '\0'; ++sc1) {
        for (sc2 = s2; *sc2 != '\0'; ++sc2) {
            if (*sc1 == *sc2)
                return (sc1 - s1);
        }
    }
    return (sc1 - s1); // terminating nulls match.
}

/* find index of first s1[i] that matches no s2[]. */
size_t czf_strspn(const char *s1, const char *s2) {
    const char *sc1, *sc2;
    for (sc1 = s1; *sc1 != '\0'; ++sc1) {
        for (sc2 = s2; ; ++sc2) {
            if (*sc2 == '\0') {
                return (sc1 - s1);
            } else if (*sc1 == *sc2) {
                break;
            }
        }
    }   
    return (sc1 - s1);
}

/* find next token in s1[] delimited by s2[]. */
char *czf_strtok(char *s1, const char *s2) {
    char *sbegin, *send;
    static char *ssave = "";
    
    sbegin = s1 ? s1 : ssave;
    sbegin += czf_strspn(sbegin, s2);
    
    if (*sbegin == '\0') {
        ssave = "";
        return NULL;
    }
    
    send = sbegin + czf_strcspn(sbegin, s2);
    if (*send != '\0')
        *send++ = '\0';
        
    ssave = send;
    return (sbegin);
}

int main(void) { 
    static char str[] = "git@github.com:user/repo.git";
    char *t;
    t = czf_strtok(str, "@");    // t point to "git"
    t = czf_strtok(NULL, ":");   // t point to "githut.com"
    t = czf_strtok(NULL, "/");   // t point to "user"
    t = czf_strtok(NULL, ".");   // t point to "repo"
    return 0;
}