ip地址转化成长整数

/**
 * reference: bash-4.1/lib/sh/inet_aton.c
 * Convert an Internet Address to a numeric address.
 * Support base 8(prefix 0..),10,16(prefix 0x..)
 * Returns 1 if the IP is valid, 0 if not.
*/
int ipton(const char *cp, unsigned long int *addr_u)
{
    int base;
    unsigned long int val;
    unsigned char c;
    unsigned int fields[4];
    unsigned int *pfield = fields;

    c = *cp;
    while( c )
    {
        if( !isdigit(c) )
            return 0;
        val = 0;
        // deal with base
        base = 10;
        if('0' == c)
        {
            c = *(++cp);
            if('x' == c || 'X' == c)
            {
                base = 16;
                c = *++cp;
            }
            else
                base = 8;
        }
        //calculate 4 parts
        for(;;)
        {
            if( isascii(c) && isdigit(c) )
            {
                val = (val * base) + (c - '0');
                c = *(++cp);
            }
            else if( (16 == base) && isascii(c) && isxdigit(c) )
            {
                c |= 0x20; /* tolower */
                val = (val << 4) | (c + 10 - 'a');
                c = *++cp;
            } else
                break;
        }
        if(val > 0xff) //max is 255
            return 0;
        if('.' == c)
        {
        // 15.25.35.45, the 3d '.', pfield point to 3
            if (pfield >= fields + 3)
                return 0;
            *pfield++ = val;
            c = *++cp;
            printf("%ld\t", val);
        } else
            break;
    }
    if( c != '\0' && ( !isascii(c) || !isspace(c) ) )
        return 0;
    if( pfield - fields +1 < 4 )
        return 0;
    printf("%ld is:\n", val);
    val |= (fields[0] << 24) | (fields[1] << 16) | (fields[2] << 8 );
    *addr_u = val;

    return 1;
}

int main(void)
{
    unsigned long int fromip;
    if( ipton("0xF8.248.0365.245 ", &fromip) > 0 )
        printf("%ul\n", fromip);

    return 0;
}