print_broadcast_addresses.cpp

#include <cstdio>
#include <string>
#include <cstring>
#include <cstdint>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <ifaddrs.h>
#include <netinet/in.h>


int main() {
    struct ifaddrs *ifap, *ifa;
    struct sockaddr_in *sa,*sb;
    char *addr;
    
    // only IPv4
    struct in_addr ips;
    struct in_addr bas;
    struct in_addr nms;
    struct in_addr computed_bas;
    
    //~ uint32_t* ips1 = (uint32_t*)(&ips);
    //~ uint32_t* nms1 = (uint32_t*)(&nms);
    //~ uint32_t* computed_bas1 = (uint32_t*)(&computed_bas);

    getifaddrs (&ifap);
    for (ifa = ifap; ifa; ifa = ifa->ifa_next) {
        if (ifa->ifa_addr->sa_family==AF_INET) {
            sa = (struct sockaddr_in *) ifa->ifa_addr;
            memcpy(&ips,&(sa->sin_addr),sizeof(struct in_addr));
            addr = inet_ntoa(sa->sin_addr);
            std::string ipAddr(addr);
            
            // if(ipAddr == "127.0.0.1") continue;
            memcpy(&computed_bas,&(sa->sin_addr),sizeof(struct in_addr)); // copy ip to bcast_ip, will be updated later
            
            sa = (struct sockaddr_in *) ifa->ifa_broadaddr;
            memcpy(&bas,&(sa->sin_addr),sizeof(struct in_addr));
            addr = inet_ntoa(sa->sin_addr);
            std::string bAddr(addr);
            
            sa = (struct sockaddr_in *) ifa->ifa_netmask;
            memcpy(&nms,&(sa->sin_addr),sizeof(struct in_addr));
            addr = inet_ntoa(sa->sin_addr);
            std::string netmask(addr);
            
            // *computed_bas1 = *ips1 | (~(*nms1));
            computed_bas.s_addr = ips.s_addr | (~(nms.s_addr));
            
            printf("Memcmp result: %d\n",!memcmp(&computed_bas,&bas,sizeof(struct in_addr))); // BEWARE OF ALIGNMENT!!!
            printf("Struct member comparison result: %d\n",computed_bas.s_addr == bas.s_addr);
            
            addr = inet_ntoa(computed_bas);
            std::string computed(addr);
            
            printf("Interface: %s\nIP address: %s\nBroadcast address: %s\nNetmask: %s\nComputed broadcast address: %s\n\n", ifa->ifa_name, ipAddr.c_str(), bAddr.c_str(), netmask.c_str(), computed.c_str());
        }
    }

    freeifaddrs(ifap);
    return 0;
}