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copied!<p>To get a fully qualified name for a machine, we must first get the local hostname, and then lookup the canonical name.</p> <p>The easiest way to do this is by first getting the local hostname using <code>uname()</code> or <code>gethostname()</code> and then performing a lookup with <code>gethostbyname()</code> and looking at the <code>h_name</code> member of the struct it returns. If you are using ANSI c, you <em>must</em> use <code>uname()</code> instead of <code>gethostname()</code>.</p> <p>Example:</p> <pre><code>char hostname[1024]; hostname[1023] = '\0'; gethostname(hostname, 1023); printf("Hostname: %s\n", hostname); struct hostent* h; h = gethostbyname(hostname); printf("h_name: %s\n", h->h_name); </code></pre> <p>Unfortunately, <code>gethostbyname()</code> is deprecated in the current POSIX specification, as it doesn't play well with IPv6. A more modern version of this code would use <code>getaddrinfo()</code>.</p> <p>Example:</p> <pre><code>struct addrinfo hints, *info, *p; int gai_result; char hostname[1024]; hostname[1023] = '\0'; gethostname(hostname, 1023); memset(&hints, 0, sizeof hints); hints.ai_family = AF_UNSPEC; /*either IPV4 or IPV6*/ hints.ai_socktype = SOCK_STREAM; hints.ai_flags = AI_CANONNAME; if ((gai_result = getaddrinfo(hostname, "http", &hints, &info)) != 0) { fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(gai_result)); exit(1); } for(p = info; p != NULL; p = p->ai_next) { printf("hostname: %s\n", p->ai_canonname); } freeaddrinfo(info); </code></pre> <p>Of course, this will only work if the machine has a FQDN to give - if not, the result of the <code>getaddrinfo()</code> ends up being the same as the unqualified hostname.</p>

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