Programming

Im trying to connect to a particular IP address and I'm tying to use gethostbyaddr() and inet_addr() to do this. However, when I tried using inet_addr(), I always get a return value of 0 when I tried to connect to "172.21.16.238". Hope someone here could help me on this. I already tried using inet_ network() but I still get the same results.

Variable declaration:
char host_name2[CHKPARAMLEN] = "172.21.16.238";
char host_name[CHKPARAMLEN];
char *index, *instring_ptr, *instringTemp_ptr, *host_name_ptr, *host_name2_ptr;


Actual Code:
...
while (*host_name2_ptr != '\0')
{
if (*host_name2_ptr != ' ')
{
*host_name_ptr = *host_name2_ptr;
++host_name_ptr ;
}
++host_name2_ptr;
}
printf("host_name after for loop: %s end\n", host_name);

addr = inet_addr(host_name_ptr);
printf("addr after inet_addr: %i \n", addr);
if (isalpha(host_name[0])) { /* host address is a name */
if (host_name[strlen(host_name)-1] == '\n')
host_name[strlen(host_name)-1] = '\0';
h = gethostbyname(host_name);
printf("host address is a name \n");
}
else
{
printf("host address is an IP address \n");
addr = inet_addr(host_name); // inet_addr returns 0 when host name is 172.21.16.238
h = gethostbyaddr((char *)&addr, sizeof addr, AF_INET);
}
if(h==0) {
printf("BMODCHK: Unknown Host '172.21.16.238' \n");
exit(1);
}

I think it is your C code, not the call. inet_addr returns a (-1) for malformed addresses. You have a lot of code which seems to be playing with the address string.
Put a

Code:

printf("host_name= %s\n", host_name);

right before you call to inet_addr()

The return value of inet_addr is and in_addr_t datatype which is an unsigned long or an unsigned int.

This means you have to cast the result to signed datatype to see if you got minus one.