errno

cynthia · 09-23-2004, 05:14 AM

my code contains the lines

x=recv(...)
if(errno = WOULD_BLOCK)...

I want to avoid a situation that in this line errno will get a value from previous calls to recv().

how can I prevent such a mistake from happening?

do I need to flush error que in order to avoid that situation?

rjlee · 09-23-2004, 05:26 AM

Quote:

Originally posted by cynthia
my code contains the lines

x=recv(...)
if(errno = WOULD_BLOCK)...

I want to avoid a situation that in this line errno will get a value from previous calls to recv().

how can I prevent such a mistake from happening?

do I need to flush error que in order to avoid that situation?

First off, you are assigning the value WOULD_BLOCK to errno, which is an error. (Note that errno can be implemented as a macro).

According to the standard, the only correct way to use errno is to set its value to 0 prior to a procedure call, and then test its value afterwards:

Code:

errno = 0;
x=recv(…);
if (errno == WOULD_BLOCK) …

Standard C does not implement an error “queue” that can be flushed as far as I am aware.

Hope that helps,

— Robert J. Lee

cynthia · 09-23-2004, 07:39 AM

that assignment works fine for UNIX. how about WINDOWS? there they call function and not using a variable?

would that function empy the queue?

rjlee · 09-24-2004, 01:58 PM

The Microsoft Windows C library extensions may well define an error queue but standard C does not.

That code will work fine in any standard C compiler, regardless of the platform. If it doesn't work in Microsoft's C compiler, then it isn't a standards-complient C compiler. In which case, my best advice is to upgrade.