Please help me...
i have problem with connect().In some situations my program don't respond for long time period,because server dont respond.How to set function connect() to conecting just 5 seconds and after that exit...which function to use for timing?

This isn't so much a sockets problem as an IPC problem. You need to use the alarm(2) system call to send your program a SIGALRM signal in a given number of seconds. Set up a signal handler with sigaction() to catch the signal and inform the user that the server is crapped-out.

Use alarm once before the connect call specifying the number of seconds and once after the connect call sending it 0 to reset the previous alarm.

I know this was very terse, but it's all in the man pages or online somewhere. Have fun.

this is not really a portable solution. In some cases a signal will cause the connect to return -1 with errno set to EINTR, but some implementations will the connect call will be restarted. It has something to do with TCP's handshake mechanism and reliability. It must wait for the otherside to issue either an ACK or an RST, if it doesn't get this right away it will block for a while. What you can do is set connect to non blocking mode and do issue a select on the socket. See fcntl for setting the socket to non blocking mode and select for your time out and connection polling.

You need to connect non-blocking or use the select() function to poll the fd of the socket.

May I recommend the Stevens "UNIX network programming" ISBN 013490012X . This is a classic and a must read for any UNIX network programmer, IMHO.

Also check out the socket FAQ at http://www.lcg.org/sock-faq/ . This document will give you a lot of the information you need.