Get all IP-Addresses in C - c

Question

I have the following problem. I have to write a Plugin for Pidgin in the Language C. I am completely new to C.
I found the following Code.
WORD wVersionRequested;
WSADATA wsaData;
char name[255];
char* ip;
PHOSTENT hostinfo;
wVersionRequested = MAKEWORD( 2, 0 );
if ( WSAStartup( wVersionRequested, &wsaData ) == 0 ) {
if( gethostname ( name, sizeof(name)) == 0) {
if((hostinfo = gethostbyname(name)) != NULL) {
ip = inet_ntoa (*(struct in_addr *)*hostinfo->h_addr_list);
}
}
WSACleanup( );
}
I have the IP-Address
172.28.52.220
But because of my VMWare I also have the IP 10.0.1.3.
In my Plugin now the IP 10.0.1.3 is assigned to my variable.
i need the IP to find out in which location of my company I am. I need hte 172...
Now I could find in the winsock2.h that *hostinfo->h_addr_list contains the list of Ip addresses. How can I assign the 172. Address to my IP_Variable?
Thank you in advance for your help!
Edit:
Just to clarify: I don´t want to have my external IP address. I need my internals.

Answer 1

Here is an example I tested on on linux. I dont have access to a Windows system until tomorrow, but can test and update the answer if required.
It is comparable to the Windows version only without the WSAStartup call at the beginning.
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <netdb.h>
int main()
{
char hostnamebuff[100];
if(gethostname(hostnamebuff, 100) == 0)
{
struct hostent* hostinfo = gethostbyname(hostnamebuff);
printf("host name is %s\n", hostnamebuff);
if(hostinfo != NULL)
{
char** paddrlist = hostinfo->h_addr_list;
printf("host list is\n");
while(*paddrlist != NULL)
{
char addrbuff[INET6_ADDRSTRLEN];
if(inet_ntop(hostinfo->h_addrtype, *paddrlist, addrbuff, hostinfo->h_addrtype == AF_INET ? INET_ADDRSTRLEN : INET6_ADDRSTRLEN))
{
printf("%s\n", addrbuff);
if(strncmp(addrbuff, "172.", 4) == 0)
{
printf("its a match\n");
break;
}
} else
{
printf("failed to convert an address\n");
}
paddrlist++;
}
} else
{
printf("failed on gethostbyname\n");
}
} else
{
printf("failed on gethostname errno=%d\n", errno);
}
}
The h_addr_list member of hostent is a NULL terminated array of pointers to char* (so its double pointer). My example shows how to traverse this. Hope it helps.
As for this distinctly smelly bit of code
ip = inet_ntoa (*(struct in_addr *)*hostinfo->h_addr_list);
This is a highly unreadable way of getting the first entry in the address list.