Problems with gethostbyname c++

Question

I've this code made in c++ to connect to a server but every time I try "gethostbyname" the value is null(or optimized away and not available).

WSADATA wsaData;
if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {
    cout << "WSAStartup failed.\n";
    system("pause");
    return 1;
}
hostent *host = gethostbyname("www.example.com");

I've tried hostent as volatile but still gives null. Is there any other way to make this work? I've tried too Optimization disabled but keeps giving null.

"Return value If no error occurs, gethostbyname returns a pointer to the hostent structure described above. Otherwise, it returns a null pointer and a specific error number can be retrieved by calling WSAGetLastError." (MSDN) — lorro, Jun 23 '16 at 21:21
What is the assumed relationship between the opened socket and the host query? — Thomas B Preusser, Jun 23 '16 at 21:23

score 4 · Accepted Answer · edited Jun 24 '16 at 00:01

4

host is null on error. Check the return value of WSAGetLastError() to figure out whats wrong.

Try calling ping www.example.com in a cmd shell to check whether the target is reachable from your machine.

To not optimize add:

if(host!=NULL && host->h_name)
    cout << "host: " << host->h_name << std::endl;

Don't store pointers returned by gethostbyname(). They are overridden on the next call by the same thread.

edited Jun 24 '16 at 00:01

Remy Lebeau

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answered Jun 23 '16 at 21:31

lexx9999

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`gethostbyname()` fails if it cannot resolve the hostname to an IP address, such as via DNS. `ping` is not the same thing as `gethosbyname()`. `ping` actually checks if the target is reachable on the network, so even if `gethosbyname()` succeeds, `ping` can still fail if there is no network route to the target. – Remy Lebeau Jun 24 '16 at 00:03
@ Remy Lebeau I did not claim that it's the same, but if ping fails, gethostbyname will likely also fail. – lexx9999 Jun 24 '16 at 00:14
that depends on how `ping` fails. `ping` may be able to resolve the host name into an IP but still not be able to actually communicate with the host machine. – Remy Lebeau Jun 24 '16 at 00:35

Problems with gethostbyname c++

1 Answers1