getaddrinfo() complete

System_Calls/showip.c

@@ -0,0 +1,62 @@
+/*
+*   Printing the linked list of struct addrinfo
+*/
+
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netdb.h>
+#include <arpa/inet.h>
+#include <netinet/in.h>
+
+int main(int argc, char* argv[] ){
+
+    struct addrinfo hints, *res, *p;
+    int status;
+    char ipstr[INET6_ADDRSTRLEN];
+
+    if( argc != 2 ){
+        fprintf(stderr, "usage: showip hostname\n");
+        return 1;
+    }
+
+    memset(&hints, 0, sizeof hints);
+    hints.ai_family = AF_UNSPEC; // IP version agnostic
+    hints.ai_socktype = SOCK_STREAM;
+
+    if((status = getaddrinfo(argv[1], NULL, &hints, &res)) != 0){
+        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status));
+        return 2;    
+    }
+
+    printf("IP address for %s:\n\n", argv[1]);
+
+    for(p = res ; p != NULL ; p = p->ai_next){
+        void *addr;
+        char *ipver;
+
+        // get the pointer to the address itself,
+        // different fields in IPv4 and IPv6:
+        if( p->ai_family == AF_INET ){
+            // IPv4
+            struct sockaddr_in *ipv4 = (struct sockaddr_in *)p->ai_addr;
+            addr = &(ipv4->sin_addr);
+            ipver = "IPv4";
+        }
+        else{
+            // IPv6
+            struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)p->ai_addr;
+            addr = &(ipv6->sin6_addr);
+            ipver = "IPv6";
+        }
+
+       //convert the IP to a string and print it:
+       inet_ntop(p->ai_family, addr, ipstr, sizeof ipstr);
+       printf("   %s: %s\n", ipver, ipstr); 
+    }
+
+    freeaddrinfo(res); // free the linked list
+    
+    return 0;
+}