How do I find the current machine s full hostname in C hostname and domain information

Question

In a C project  POSIX   how do I get the fully qualified name for the current system   For example  I can get just the hostname of my machine by doing gethostname   from unistd h  This might give me machine3 in return  but I m actually looking for machine3 somedomain com for example   How do I go about getting this information  I do not want to use a call to system   to do this  if possible

User · Accepted Answer

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.

User · Answer

I believe you are looking for    gethostbyaddress  Just pass it the localhost IP   There is also a gethostbyname function  that is also usefull

User · Answer

The easy way  try uname    If that does not work  use gethostname   then gethostbyname   and finally gethostbyaddr    The h name of hostent   should be your FQDN

User · Answer

gethostname   is POSIX way to get local host name  Check out man   BSD function getdomainname   can give you domain name so you can build fully qualified hostname  There is no POSIX way to get a domain I m afraid

User · Answer

I believe you are looking for    gethostbyaddress  Just pass it the localhost IP   There is also a gethostbyname function  that is also usefull

User · Answer

My solution    ifdef WIN32      include  lt Windows h gt       include  lt tchar h gt   else      include  lt unistd h gt   endif  void GetMachineName char machineName 150         char Name 150       int i 0        ifdef WIN32         TCHAR infoBuf 150           DWORD bufCharCount   150          memset Name  0  150           if  GetComputerName  infoBuf   amp bufCharCount                           for i 0  i lt 150  i                                  Name i    infoBuf i                                   else                       strcpy Name   Unknown Host Name                   else         memset Name  0  150           gethostname Name  150        endif     strncpy machineName Name  150

User · Answer

gethostname   is POSIX way to get local host name  Check out man   BSD function getdomainname   can give you domain name so you can build fully qualified hostname  There is no POSIX way to get a domain I m afraid

User · Answer

I believe you are looking for    gethostbyaddress  Just pass it the localhost IP   There is also a gethostbyname function  that is also usefull

User · Answer

gethostname   is POSIX way to get local host name  Check out man   BSD function getdomainname   can give you domain name so you can build fully qualified hostname  There is no POSIX way to get a domain I m afraid

User · Answer

The easy way  try uname    If that does not work  use gethostname   then gethostbyname   and finally gethostbyaddr    The h name of hostent   should be your FQDN

User · Answer

gethostname   is POSIX way to get local host name  Check out man   BSD function getdomainname   can give you domain name so you can build fully qualified hostname  There is no POSIX way to get a domain I m afraid

User · Answer

My solution    ifdef WIN32      include  lt Windows h gt       include  lt tchar h gt   else      include  lt unistd h gt   endif  void GetMachineName char machineName 150         char Name 150       int i 0        ifdef WIN32         TCHAR infoBuf 150           DWORD bufCharCount   150          memset Name  0  150           if  GetComputerName  infoBuf   amp bufCharCount                           for i 0  i lt 150  i                                  Name i    infoBuf i                                   else                       strcpy Name   Unknown Host Name                   else         memset Name  0  150           gethostname Name  150        endif     strncpy machineName Name  150

User · Answer

The easy way  try uname    If that does not work  use gethostname   then gethostbyname   and finally gethostbyaddr    The h name of hostent   should be your FQDN

User · Answer

The easy way  try uname    If that does not work  use gethostname   then gethostbyname   and finally gethostbyaddr    The h name of hostent   should be your FQDN

User · Answer

I believe you are looking for    gethostbyaddress  Just pass it the localhost IP   There is also a gethostbyname function  that is also usefull

[c] How do I find the current machine's full hostname in C (hostname and domain information)?

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