How do I find the current machine’s full hostname in C (hostname and domain information)?

by

To get a fully qualified name for a machine, we must first get the local hostname, and then lookup the canonical name.

The easiest way to do this is by first getting the local hostname using uname() or gethostname() and then performing a lookup with gethostbyname() and looking at the h_name member of the struct it returns. If you are using ANSI c, you must use uname() instead of gethostname().

Example:

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);

Unfortunately, gethostbyname() is deprecated in the current POSIX specification, as it doesn’t play well with IPv6. A more modern version of this code would use getaddrinfo().

Example:

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);

Of course, this will only work if the machine has a FQDN to give – if not, the result of the getaddrinfo() ends up being the same as the unqualified hostname.

More Related Contents:

  1. Is there a way to flush a POSIX socket?
  2. Is it possible (and safe) to make an accepting socket non-blocking?
  3. Connection refused – tcp socket in linux [closed]
  4. Return value range of the main function
  5. Passing a structure through Sockets in C
  6. When should I use mmap for file access?
  7. Differ between header and content of http server response (sockets)
  8. How to set socket timeout in C when making multiple connections?
  9. Connecting n commands with pipes in a shell?
  10. Understanding INADDR_ANY for socket programming
  11. Kill Thread in Pthread Library
  12. Why do we cast sockaddr_in to sockaddr when calling bind()?
  13. How to make an HTTP get request in C without libcurl?
  14. Checking if a file is a directory or just a file [duplicate]
  15. How can I convert a file pointer ( FILE* fp ) to a file descriptor (int fd)?
  16. How to get the current time in milliseconds from C in Linux?
  17. Why changing value of SO_RCVBUF doesn’t work?
  18. Where to find the complete definition of off_t type?
  19. Create statically-linked binary that uses getaddrinfo?
  20. How do I use setsockopt(SO_REUSEADDR)?
  21. How large should my recv buffer be when calling recv in the socket library
  22. Is snprintf() ALWAYS null terminating?
  23. Redirect stdout to a file
  24. How to use nanosleep() in C? What are `tim.tv_sec` and `tim.tv_nsec`?
  25. bind socket to network interface
  26. Strange RAW Socket on Mac OS X
  27. How to convert from UTC to local time in C?
  28. What can cause a “Resource temporarily unavailable” on sock send() command
  29. Checking if errno != EINTR: what does it mean?
  30. What is the difference between AF_INET and PF_INET in socket programming?

Leave a Comment