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// Using getnameinfo() to get host name for a
// given IP address (argv[1]).
//
// P. Kearns, February 2009
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char **argv)
{
int ecode;
struct in_addr fillin;
struct sockaddr_in addr;
char host[NI_MAXHOST];
if (argc != 2) {
fprintf(stderr,"usage: gethost address\n");
exit(1);
}
// Dotted decimal to binary IP address.
ecode = inet_pton(AF_INET, argv[1], &fillin);
if (ecode == 0) {
fprintf(stderr,"inet_pton: invalid address\n");
exit(1);
}
if (ecode < 0) {
perror("inet_pton"); exit(1);
exit(1);
}
// Fill in blanks of a sockaddr_in after zeroing it out.
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(0);
memcpy(&(addr.sin_addr), &fillin, sizeof(addr.sin_addr));
// Do the lookup.
ecode = getnameinfo((struct sockaddr *) &addr, sizeof(addr),
host, NI_MAXHOST, NULL, 0, NI_NAMEREQD);
if (ecode) {
fprintf(stderr, "getnameinfo: %s\n", gai_strerror(ecode));
exit(1);
}
printf("Hostname: %s\n", host);
exit(0);
}
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