Basic understanding on winsock select()

Kjeksen · #1 30-Aug-2005, 05:59

Hey! I im pretty new in winsock. And i want to learn more about it and its functions. So I will ask some questions about different matters in select so i can understand it. Beej`s tutorial doesnt have so good explenations about it.

What about this one.

CPP / C++ / C Code:

if(select(fdmax+1, &read_fds, NULL, NULL, NULL) == -1) {
                        cerr << "Error in select()";
                        cin.get();
                        exit(1);
                        }

Can someone give me a basic explenation on this one? why are there NULL, NULL and NULL?

L7Sqr · #2 30-Aug-2005, 07:42

select watches for status changes on the file descriptors designated by the second,third and fourth fields of the call.
The fields represent (..., read_fd, write_fd, exectption_fd,...)
Passing NULL to any of these fields says that you do not care what happens there. In your case - `I'm not interested in my file descriptors changing status for writing or execption purposes, only for read changes`.
The final field represents a timeout option. If passed NULL, it means you want to have a blocking call (it wont return until something happens).
Google man select for the manual pages detailing the call's specifics.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Rate This Thread
Rate This Thread:

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[PROGRAM] Winsock Programming	Max Payne	MS Visual C++ / MFC Forum	1	08-Mar-2007 23:38
MSDN's Great Contribution To Understanding Dial Up Networking...	mithunjacob	Open Discussion Forum	2	25-Jun-2004 05:36
select problem	zuzupus	MySQL / PHP Forum	0	15-Aug-2003 07:25
combo box select problem	zuzupus	MySQL / PHP Forum	2	23-Jul-2003 11:25