Get subnet mask

[fmaurer]

Hi, I am the very beginner in network programming and need to find a way to show all IP addresses being in the same network. I considered solution of getting machine's IP and subnet mask and perform some bit operations. I've already found the code to get the IP address of the local machine

#include <iostream>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <string>


 int GetHostIP()
{
    char *Ip;
    WSADATA wsaData;
    struct hostent *pHostEnt=NULL; 
    struct sockaddr_in tmpSockAddr; //placeholder for the ip address

    // Not needed if it is already taken care by some other part of the application
    WSAStartup(MAKEWORD(2,0),&wsaData); 

    char hostname[100]; //assume windows doesn't allow having longer hostnames
	gethostname(hostname, sizeof hostname);
    //This will retrieve the ip details and put it into pHostEnt structure
    pHostEnt = gethostbyname(hostname);

    if(pHostEnt == NULL)
    {
        printf("Error occured: %s\n",GetLastError());
		WSACleanup();
        return 1;
    }

but still have no idea how to get a subnet mask.
I would be grateful for any suggestions