socket() programming question!

[peter ho]

Hope that anyone can help me. I am new to socket() programming. I try to connect to a tcp server. However my program fails when its get to gethostbyaddr() function. It keeps returning "null". My questions are: 1) Is there a difference between AF_INET and PF_INET? 2) The gethostbyaddr() returns "null" because it can't not see the tcp server IP on the network for some reason ?(eventhough I can ping or telnet to tcp server) Many thanks! peter. unsigned int addr; struct hostent *hp; SOCKET conn; conn=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP); addr=inet_addr("10.23.50.133"); hp=gethostbyaddr((char*)&addr,sizeof(addr),AF_INET);

[Joseph Dempsey]

well here are a couple of things: 1) Make sure you have initialized the winsock library. if you haven't that function would also return null. It sounds trivial but i have forgotten this many a time just to find out it was some simple mistake such as not loading the library. Load it like this:

int nRet = 0;
WSADATA wsd; //information object to hold info from library startup
memset( &wsd, 0, sizeof( WSADATA ) );
nRet = WSAStartup( MAKEWORD( 2, 2 ), &wsd ); //load and start the library.

2. There is a difference between AF_INET and PF_INET even though they are numerically the same. You should not rely on that fact because one day those numbers may change. The PF is a protocol family and the AF is an address family. 3) If all else fails you can have a look at this. I wrote this code awhile ago for my own library and use it frequently so i know it works.

BOOL ConnectServ( SOCKET* pSock, LPCSTR sServ, LPCSTR sPort, BOOL bOverlapped )
{
BOOL bConn = FALSE;
ADDRINFO* pAI = NULL;
int nRet = 0; // number known not to be SOCKET_ERROR
DWORD dwFlags = 0;

if( ! pSock ) {
return FALSE;
}

if( getaddrinfo( sServ, sPort, NULL, &pAI ) != 0 ) {
return FALSE;
}

if( bOverlapped ) {
dwFlags = WSA_FLAG_OVERLAPPED;
}

*pSock = WSASocket( PF_INET, SOCK_STREAM, 0, NULL, 0, dwFlags );
if( IsValidSocket( *pSock ) ) {
nRet = WSAConnect( *pSock, pAI->ai_addr, ( int )pAI->ai_addrlen, NULL, NULL, NULL, NULL );
if( nRet == SOCKET_ERROR ) {
CloseConn( *pSock );
}else{
bConn = TRUE;
}
}

freeaddrinfo( pAI );

Good luck. Joseph Dempsey joseph_r_dempsey@yahoo.com "Software Engineering is a race between the programmers, trying to make bigger and better fool-proof software, and the universe trying to make bigger fools. So far the Universe in winning." --anonymous