is_valid_ip_addr

/*
 * return value:
 * 1: succ
 * 0: not
 * */
static int is_valid_ip_addr(const char* ip)
{
    const char* str = ip;
    int i = 0;
    int j = 0;
    int number = 0;
    int number_count = 0;

    if(str[0] == '.') 
	return 0;

    while(ip[i] != '\0')
    {
	if (number_count == 4)
	{
	    return 0;
	}

	if((ip[i] != '.') && ((ip[i] < '0') || (ip[i] > '9')))// neither is '.' nor is a number
	{
	    return 0;
	}

	if(ip[i] == '.')
	{ 
	    number = atoi(str);
	    if ((number < 0) || (number > 255))
		return 0;
	    //printf("number = %d\n", number);

	    str = ip + i + 1;
	    if(str[0] == '\0')//the last char is '.'
	    {
		return 0;
	    }

	    ++number_count;
	}
	i++;
    }

    if(number_count <= 2) 
	return 0;

    if(number_count == 3) 
    {
	number = atoi(str);
	if ((number < 0) || (number > 255))
	    return 0;
	printf("number = %d\n", number);
	return 1;
    }
    return 1;
}