Confused about memset

[the transltr]

I am studying socket programming and i encountered this code.

#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);
            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;
}

I understand it all except one. Why this code memset'ed the struct hints but not the *res and *p?

[ne555]

[code] "Please use code tags" [/code]
Because you don't care about the value of those pointers.
res is initialized in the getaddrinfo() call, and 'p' in the loop (to traverse the list)

[the transltr]

So i can memset *res, however it doesn't make sense because the getaddrinfo() will overwrite it anyway?

[ne555]

memset(&res, //... quite obfuscated way for initializing a pointer.
You must not memset(res, //... because res is pointing to garbage.
And certainly not memset(*res, //... as it will not compile.

But yes, getaddrinfo() will set the value for res

[the transltr]

Thank you!