/* This function will return the first occurrence of a string, without the terminator '\0'.  */
char* rt_strstr(const char *s1, const char *s2)
/* This function will return the first occurrence of a string, without the terminator '\0'.  */
char* rt_strstr(const char *s1, const char *s2)
{
    int l1 = 0, l2 = 0;
    l2 = rt_strlen(s2);
    if (!l2)
    {
        return (char *)s1;
    }
    l1 = rt_strlen(s1);
    while (l1 >= l2)
    {
        l1 --;
        if (!rt_memcmp(s1, s2, l2))
        {
            return (char *)s1;
        }
        s1 ++;
    }
    return RT_NULL;
}