Functions Failing When Embedded In If()

dexter

Jun 14 2005, 03:45 PM

I've had this problem on and off over the years (me just being silly, generally), so I thought I might share how to fix it. This has come up several time whilst using sockets, actually, so here's an example.

For instance,

CODE

if(hd_ = bind(AF_INET, SOCK_STREAM, IPPROTO_TCP) <= 0) {
perror("socket() failure");
exit(1);
}

What's the problem?

The problem is that,

CODE

hd_ = bind(AF_INET, SOCK_STREAM, IPPROTO_TCP)

should be encapsulated within parentheses.

Why?

When the call is made, a comparison between the return value and the 0 is made, and the boolean value (0 or 1) is then assigned to hd_, thus causing the value 0 to be stored in hd_ every time, but at the same time, skipping the error catching code.

So, instead:

CODE

if((hd_ = bind(AF_INET, SOCK_STREAM, IPPROTO_TCP)) <= 0) {
perror("socket() failure");
exit(1);
}

This will then work just as it's supposed to.
Watch yer parentheses when embedding...

dexter

Jun 14 2005, 03:48 PM

Ahem... I'm quite aware that socket() returns -1 for an error, and 0 is possible as a file descriptor value. The comparisons there should've actually been '<' not '<='. That was just from me trying to pin down the problem, and to show an example of how it can go wrong... neeeeed edit.

osknockout

Jun 18 2005, 11:20 AM

WOow, interesting changes to the t17 skins.
Actually dexter, if you were like the rest of us, you'd stop assigning
the bind function to hd and you'd start testing if it was equal.

==, not =. So the code should read

CODE

if(hd_ == bind(AF_INET, SOCK_STREAM, IPPROTO_TCP) <= 0) {
perror("socket() failure");
exit(1);
}

Unless VC++ has some weird mechanism to understand = equals == in parentheses

dexter

Jun 18 2005, 11:31 AM

Erm... actually, looking back, I made an error. The call should've been socket(), not bind(), thus the perror("socket() failed"). I even mentioned the right call in the second post I made.

The value was being assigned to hd_ to keep the value of the socket that was created for the host...

And yeah, when I use bind, I don't assign the value to anything, I just do a comparison.

QUOTE

Unless VC++ has some weird mechanism to understand = equals == in parentheses

Nope. Don't touch VC++ these days. Too many non-standard featurs.

Gcc is the only way to go.

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Functions Failing When Embedded In If() - Just a beserk problem that's plagued me on and off for years

Functions Failing When Embedded In If() - Just a beserk problem that's plagued me on and off for years