hostname.c

/*----- Find host name from IP address -----*/

#include <stdio.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>

int main(int argc, char* argv[]){
    struct hostent* hent; // host structure
    struct in_addr ip; // ip structure
    const char *ipstr = argv[1];
    // "172.217.166.228" => www.google.com (domain name)
    inet_aton(ipstr, &ip);
    hent = gethostbyaddr((const void *)&ip, sizeof(ip), AF_INET);
    if(hent){
        printf("%s\n", hent->h_name);
    }
    else{
        printf("Something went wrong...\n");
    }
    return 0;
}