Unix Programming - Get host name from IP address

Author

Get host name from IP address

Christian

2004-12-28, 9:12 am

Hello guys,

I'm trying to write a simple function which would return the FQDN of a host
from its IPaddress :

int main( int argc, char *argv[] ) {

int len;
char answer[4096];

if( res_init( ) != 0 )
return -1;

len = res_query( argv[1], C_IN, T_A, answer, 4096 );
printf( "len = %d\nerr = %d\n", len, h_errno);

return 0;
}

But if argv[1] is an IP address, res_query returns -1 with h_errno = 1
(Operation not permitted).
If argv[1] is, say, www.yahoo.com, no errors occurs.

Any idea of what's wrong ?

Thanks

Christian

DINH Viet Hoa

2004-12-28, 9:12 am

Christian wrote :

> But if argv[1] is an IP address, res_query returns -1 with h_errno = 1
> (Operation not permitted).

Why not use gethostbyname() ?

You'll get a hostent structure that will contain the host name.

--
DINH V. Hoa,

"tuning et dope, aucun rapport" -- b.

Christian

2004-12-28, 9:12 am

"DINH Viet Hoa" <dinh.viet.hoa@free.fr> a écrit dans le message de
news:etPan.41d14058.34c9249f.3d6d@utopia...
> Christian wrote :
>
>
> Why not use gethostbyname() ?
>
> You'll get a hostent structure that will contain the host name.
>
> --
> DINH V. Hoa,
>
> "tuning et dope, aucun rapport" -- b.
>

gethostbyname() with www.yahoo.fr gives :
h_name = www.euro.yahoo.akadns.net
h_aliases = www.yahoo.fr

but with 193.108.197.230, it gives :
h_name = 193.108.197.230

i want a function that would return h230.cornut.fr from 193.108.197.230.

Any other idea ?

Bjorn Reese

2004-12-28, 9:12 am

Christian wrote:

> i want a function that would return h230.cornut.fr from 193.108.197.230.
>
> Any other idea ?

gethostbyaddr()

--
mail1dotstofanetdotdk

Christian

2004-12-28, 9:12 am

"Bjorn Reese" <breese@see.signature> a écrit dans le message de
news:41d1512b$0$671$ba624c82@nntp02.dk.telia.net...
> Christian wrote:
>
>
> gethostbyaddr()
>
> --
> mail1dotstofanetdotdk

That's exactly what I wanted !

Thanks to you Bjorn, and also Dinh

surendran.d@gmail.com

2004-12-30, 8:57 am

just use

int gethostname(char *name, size_t len);

use the header

#include <unistd.h>, for more information just search
in BEEJ's network programming

all the best

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