help ! gethostbyaddr error

hi!
when i use gethostbyaddr £¬it can only own ip's hostname£¬otherip
all can't £¬but gethostbyname is work fine £¬and dns is also fine¡£ my
system is debian £¬kernel is 2.6.18
code is following:

int main(int argc,char **argv)
{
struct sockaddr_in addr;
memset(&addr,0,sizeof(struct sockaddr_in));


addr.sin_family=PF_INET;
addr.sin_port=htons(80);

inet_pton(PF_INET,argv[1],&addr.sin_addr);


struct hostent *h;

h=gethostbyaddr((const void *)&addr.sin_addr,sizeof(struct
in_addr),PF_INET);
//h=gethostbyname(argv[1]);
if(h==NULL)
printf("%s host name is error \n",argv[1]);


struct in_addr a;
a.s_addr=inet_addr(argv[1]);
h=gethostbyaddr((char*)&a,sizeof(a),PF_INET);
if(h!=NULL)
printf("%s host name is %s\n",argv[1],h->h_name);

return 0;
}

i means it can only get my own hostname,all other ip'hostname
can't ,it return null and p_errno=1

On 6ÔÂ1ÈÕ, ÏÂÎç8ʱ49·Ö, step <fxl...@gmail.com> wrote:
> hi!
> when i use gethostbyaddr £¬it can only own ip's hostname£¬other ip
> all can't £¬but gethostbyname is work fine £¬and dns is also fine¡£ my
> system is debian £¬kernel is 2.6.18
> code is following:
>
> int main(int argc,char **argv)
> {
> struct sockaddr_in addr;
> memset(&addr,0,sizeof(struct sockaddr_in));
>
> addr.sin_family=PF_INET;
> addr.sin_port=htons(80);
>
> inet_pton(PF_INET,argv[1],&addr.sin_addr);
>
> struct hostent *h;
>
> h=gethostbyaddr((const void *)&addr.sin_addr,sizeof(struct
> in_addr),PF_INET);
> //h=gethostbyname(argv[1]);
> if(h==NULL)
> printf("%s host name is error \n",argv[1]);
>
> struct in_addr a;
> a.s_addr=inet_addr(argv[1]);
> h=gethostbyaddr((char*)&a,sizeof(a),PF_INET);
> if(h!=NULL)
> printf("%s host name is %s\n",argv[1],h->h_name);
>
> return 0;
>
> }

step schrub im Jahre 01.06.2007 14:49:
> hi!
> when i use gethostbyaddr £¬it can only own ip's hostname£¬other ip
> all can't £¬but gethostbyname is work fine £¬and dns is also fine¡£ my
> system is debian £¬kernel is 2.6.18

better use getaddrinfo() This will also help in being IPv6-save.

step <(E-Mail Removed)> wrote:
> i means it can only get my own hostname,all other ip'hostname
> can't ,it return null and p_errno=1

Probably want to check the settings in places like /etc/nsswitch.conf
to see if your "name resolution" stuff is configured to use anything
other than "files" (eg /etc/hosts). I'd have thought it would use the
same entries as gethostbyname, but stranger things have happened I
suppose. You could also try taking a system call trace of your code
to see which files are being examined for settings and/or values.

You could also try the experiment of adding a test entry in your
/etc/hosts file and see if your gethostbyaddr() call can find it.

And as someone else points-out, folks using
gethostbyname/gethostbyaddr should really be using
getaddrinfo/getnodeinfo these days. Even if the application isn't
interested in IPv6 yet, the newer interfaces are IMO nicer to use, and
someday someone, perhaps even you, will want the app to work with IPv6

rick jones
--
firebug n, the idiot who tosses a lit cigarette out his car window
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

On 6ÔÂ2ÈÕ, ÉÏÎç1ʱ30·Ö, Rick Jones <rick.jon...@hp.com> wrote:
> step <fxl...@gmail.com> wrote:
> > i means it can only get my own hostname,all other ip'hostname
> > can't ,it return null and p_errno=1
>
> Probably want to check the settings in places like /etc/nsswitch.conf
> to see if your "name resolution" stuff is configured to use anything
> other than "files" (eg /etc/hosts). I'd have thought it would use the
> same entries as gethostbyname, but stranger things have happened I
> suppose. You could also try taking a system call trace of your code
> to see which files are being examined for settings and/or values.
>
> You could also try the experiment of adding a test entry in your
> /etc/hosts file and see if your gethostbyaddr() call can find it.
>
> And as someone else points-out, folks using
> gethostbyname/gethostbyaddr should really be using
> getaddrinfo/getnodeinfo these days. Even if the application isn't
> interested in IPv6 yet, the newer interfaces are IMO nicer to use, and
> someday someone, perhaps even you, will want the app to work with IPv6
>
> rick jones
> --
> firebug n, the idiot who tosses a lit cigarette out his car window
> these opinions are mine, all mine; HP might not want them anyway...
> feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

thanks,i find the problem, it because dns server don't support ip->
domain resolving,

step <(E-Mail Removed)> wrote:
> thanks,i find the problem, it because dns server don't support ip->
> domain resolving,

Sounds like it is time to send a nasty note to hostmaster.

rick jones
--
portable adj, code that compiles under more than one compiler
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...