recv() without waiting...

eam · 02-28-2005, 12:21 AM

recv() just waits until the server sends something. Is there any way to use recv() (or a similar function) to get text if its sent but continue on if its not?

**Thantos** · 02-28-2005, 12:36 AM

What you do is to use select() to see if the socket is avialable to read from, if it is you do the read, if not you move on.

eam · 02-28-2005, 12:49 AM

Do you know where I could find a decent select() example?

**Thantos** · 02-28-2005, 12:59 AM

Yes in fact I do.

Since I want you to work for it I'll give you a couple of hints instead of flat out telling you:
Networking/Device Communication, search, Beej, select

eam · 02-28-2005, 01:21 AM

Aww Beej's example is the example I found to be "undecent." One is too simplified (stdin! how do I do this with sockets?) and the other is too complex...

Thanks anyway.

**Salem** · 02-28-2005, 01:27 AM

http://cboard.cprogramming.com/search.php
Search: Key Word(s): select, recv Showing results 1 to 20 of 20 Search took 0.32 seconds.

eam · 02-28-2005, 01:59 AM

It still waits... What'd I do wrong?

Code:

fd_set readfds;
struct timeval count;
FD_ZERO(&readfds);
FD_SET(sockfd, &readfds);
select(0, &readfds, 0, 0, &count);
if (FD_ISSET(sockfd, &readfds))
{	
     if ((bytes=recv(sockfd, buffer2, 200, 0)) == -1) {
          return 0;
     }
}

**Salem** · 02-28-2005, 02:28 AM

> What'd I do wrong?
You didn't initialise count
You didn't check the return result

Da-Nuka · 02-28-2005, 09:51 AM

Im no expert here, but might WSAAsyncSelect fulfil your requirements?

http://msdn.microsoft.com/library/en...ncselect_2.asp

What it does: It makes all the WINSOCK functions which usually waits for such things as you desribed, before moving on. This often hang your programs. This function makes such functions return if nothing are found, and when they succseed(or something else, which you can pass as a parameter), they send your program a WM_SOMETHING instead

Looks to me like this is exactly what you need?

Moore info about this can also be found at the botttom of this page:
http://www.hal-pc.org/~johnnie2/winsock.html

A sweet tutorial..

azteched · 02-28-2005, 11:13 AM

Yes, WSAAsyncSelect or other related functions are probably more appropriate for a Windows app.

**Thantos** · 02-28-2005, 12:25 PM

Of course no where has it been said if this is for a Window's app. select() is a better solution if you want it to be cross platform.

Quote:

Aww Beej's example is the example I found to be "undecent." One is too simplified (stdin! how do I do this with sockets?) and the other is too complex...

Thats the beauty of it all, you do it exactly the same way.

You need to initalize your count with the maxiumn timeout value. After the call it's value can be how much time was left (or is it how long did it wait) or the same value. You can't be exactly sure so each time you have to reset count.

**Hammer** · 02-28-2005, 06:23 PM

Another example:
http://faq.cprogramming.com/cgi-bin/...=1045780608#03

bithub · 02-28-2005, 07:29 PM

Code:

select(0, &readfds, 0, 0, &count);

If you are running this on a non-windows machine, the above line will not work. The first parameter needs to be sockfd+1. If it is a windows machine, then the first value passed to select() is ignored, so it doesn't matter.

02-28-2005, 12:21 AM	#1
eam Registered User Join Date: Oct 2003 Posts: 53	recv() without waiting... recv() just waits until the server sends something. Is there any way to use recv() (or a similar function) to get text if its sent but continue on if its not?
eam is offline

02-28-2005, 12:36 AM	#2
Thantos & the hat of GPL slaying Join Date: Sep 2001 Posts: 5,732	What you do is to use select() to see if the socket is avialable to read from, if it is you do the read, if not you move on.
Thantos is offline

02-28-2005, 12:49 AM	#3
eam Registered User Join Date: Oct 2003 Posts: 53	Do you know where I could find a decent select() example?
eam is offline

02-28-2005, 12:59 AM	#4
Thantos & the hat of GPL slaying Join Date: Sep 2001 Posts: 5,732	Yes in fact I do. Since I want you to work for it I'll give you a couple of hints instead of flat out telling you: Networking/Device Communication, search, Beej, select
Thantos is offline

02-28-2005, 01:21 AM	#5
eam Registered User Join Date: Oct 2003 Posts: 53	Aww Beej's example is the example I found to be "undecent." One is too simplified (stdin! how do I do this with sockets?) and the other is too complex... Thanks anyway.
eam is offline

02-28-2005, 01:27 AM	#6
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,683	http://cboard.cprogramming.com/search.php Search: Key Word(s): select, recv Showing results 1 to 20 of 20 Search took 0.32 seconds. __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

02-28-2005, 02:28 AM	#8
Salem and the hat of Jobseeking Join Date: Aug 2001 Location: The edge of the known universe Posts: 21,683	> What'd I do wrong? You didn't initialise count You didn't check the return result __________________ If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
Salem is offline

02-28-2005, 09:51 AM	#9
Da-Nuka Politics&Cpp geek Join Date: Oct 2004 Posts: 104	Im no expert here, but might WSAAsyncSelect fulfil your requirements? http://msdn.microsoft.com/library/en...ncselect_2.asp What it does: It makes all the WINSOCK functions which usually waits for such things as you desribed, before moving on. This often hang your programs. This function makes such functions return if nothing are found, and when they succseed(or something else, which you can pass as a parameter), they send your program a WM_SOMETHING instead Looks to me like this is exactly what you need? Moore info about this can also be found at the botttom of this page: http://www.hal-pc.org/~johnnie2/winsock.html A sweet tutorial.. __________________ http://livebad.com/nuka Da-Nuka Last edited by Da-Nuka; 02-28-2005 at 09:54 AM.
Da-Nuka is offline

02-28-2005, 11:13 AM	#10
azteched Registered User Join Date: Dec 2004 Posts: 95	Yes, WSAAsyncSelect or other related functions are probably more appropriate for a Windows app.
azteched is offline

02-28-2005, 06:23 PM	#12
Hammer End Of Line Join Date: Apr 2002 Posts: 6,240	Another example: http://faq.cprogramming.com/cgi-bin/...=1045780608#03 __________________ When all else fails, read the instructions. If you're posting code, use code tags: [code] /* insert code here */ [/code]
Hammer is offline

02-28-2005, 07:29 PM	#13
bithub Registered User Join Date: Sep 2004 Location: California Posts: 3,020	Code: select(0, &readfds, 0, 0, &count); If you are running this on a non-windows machine, the above line will not work. The first parameter needs to be sockfd+1. If it is a windows machine, then the first value passed to select() is ignored, so it doesn't matter.
bithub is offline

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