1 files changed, 57 insertions, 0 deletions
diff --git a/pgm4/inet_addrs.d/gethost.c b/pgm4/inet_addrs.d/gethost.c
new file mode 100644
index 0000000..dcfc7fd
--- /dev/null
+++ b/pgm4/inet_addrs.d/gethost.c
@@ -0,0 +1,57 @@
+// 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);
+}