Sample getaddrinfo Code Compiles in Linux but not FreeBSD.

[Peter Andreev]

2012/1/18 Martin McCormick <martin at dc.cis.okstate.edu>

>        Here is a sample program kindly provided in the
>                      Beej's Guide to Network Programming
>
> Using Internet Sockets
>
>   Brian "Beej Jorgensen" Hall
>
>        The code is said to be in the public domain so it is
> posted here as it compiles and runs perfectly under Linux but
> fails in two places with the following errors: I named it nsl.c.
>
> nsl.c: In function 'main':
> nsl.c:38: error: dereferencing pointer to incomplete type
> nsl.c:42: error: dereferencing pointer to incomplete type
>
>        You will see that in both places, the code was
> performing the same operation of assigning a value to a pointer
> so I am suspecting a prototyping issue but am not sure and hope
> someone can help me cut through the forest a little more quickly.
> He did provide suggestions for users of Sunos who have reported
> errors, but for FreeBSD, the errors did not change. Here is the
> sample code with the two error-generating lines marked.
>
> #include <stdio.h>
> #include <string.h>
> #include <sys/types.h>
> #include <sys/socket.h>
> #include <netdb.h>
> #include <arpa/inet.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; // AF_INET or AF_INET6 to force version
>    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 addresses 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);/*error*/
>            ipver = "IPv4";
>        } else { // IPv6
>            struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)p->ai_addr;
>            addr = &(ipv6->sin6_addr);/*error*/
>            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;
> }
>

#include <netinet/in.h>


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