Linux networking (gethostbyaddr) - c

Question

I am trying to get host information about the host with IP address 89.249.207.231. I know that it exists, because when I type the IP address in my browser's url field it finds the page. Here is my code in C.
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <errno.h>
int main()
{
struct in_addr addr;
inet_aton("89.249.207.231", &addr);
struct hostent* esu = gethostbyaddr((const char*)&addr),sizeof(addr), AF_INET);
printf("%s\n", esu->h_name);
return 0;
}
When I compile and run it, it gives "Segmentation fault". I can not understand the problem with my code.
Any hints and suggestions would be appreciated.
Thanks!

Answer 1

Even if the host exists, you may not be able to extract its hostname.
For example, the following code, without the deprecated functions that you use gives the result host=google-public-dns-a.google.com whereas with your host address gives could not resolve hostname.
The reason of your segfault, is that esu is NULL, because the function could not resolve a hostname by the given IP.
Here is the code:
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
int main()
{
struct sockaddr_in sa; /* input */
socklen_t len; /* input */
char hbuf[NI_MAXHOST];
memset(&sa, 0, sizeof(struct sockaddr_in));
/* For IPv4*/
sa.sin_family = AF_INET;
sa.sin_addr.s_addr = inet_addr("8.8.8.8");
len = sizeof(struct sockaddr_in);
if (getnameinfo((struct sockaddr *) &sa, len, hbuf, sizeof(hbuf),
NULL, 0, NI_NAMEREQD)) {
printf("could not resolve hostname\n");
}
else {
printf("host=%s\n", hbuf);
}
return 0;
}