addr_and_hostname.c

#include <arpa/inet.h>
#include <net/if.h>
#include <ifaddrs.h>
#include <netdb.h>
#include <stdio.h>

int main(int argc, char* argv[], char* envp[]) {
    struct ifaddrs *ifa=NULL,*ifEntry=NULL;
    void *addPtr = NULL;
    int rc = 0;
    int family, addrLen, ret;
    char addressBuffer[INET6_ADDRSTRLEN];
    char hostnameBuffer[255];

    rc = getifaddrs(&ifa);
    if (rc == 0) {
        for (ifEntry=ifa; ifEntry!=NULL; ifEntry=ifEntry->ifa_next) {
            if (ifEntry->ifa_addr == NULL) {
                continue;
            }

            if (!(ifEntry->ifa_flags & IFF_UP)) {
                continue;
            }

            if(ifEntry->ifa_addr->sa_data == NULL) {
                continue;
            }

            family = ifEntry->ifa_addr->sa_family;

            addrLen = (family == AF_INET) ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6);

            if (family == AF_INET) {
                 addPtr = &((struct sockaddr_in *)ifEntry->ifa_addr)->sin_addr;
            } else if(family == AF_INET6) {
                 addPtr = &((struct sockaddr_in6 *)ifEntry->ifa_addr)->sin6_addr;
            } else {
              continue;
            }

            const char *a = inet_ntop(family, addPtr, addressBuffer, sizeof(addressBuffer));

            ret = getnameinfo(ifEntry->ifa_addr, addrLen, hostnameBuffer, sizeof(hostnameBuffer), NULL, 0, NI_NAMEREQD);
            if (ret != 0) {
                errx(1, "%s", gai_strerror(ret));
            } else
                printf("%s %s\n", addressBuffer, hostnameBuffer);
        }
    }

    freeifaddrs(ifa);
    return 0;
}