Is this the most pointless code ever, or am I missing something?

**maxhavoc** · 07-06-2006

Is there any point to doing this?

Code:

do
{
//Whatever code you want here
}
while (0)

Correct me if I'm horribly mistaken, but doesn't this loop do nothing? The code will run once and only once because it's a post-condition loop. Wouldn't this be exactly the same thing as just having the code within the loop by itself?

**Mario F.** · 07-06-2006

Yes. The Do While statement there is unnecessary. The literal integer basically ruins its purpose.

**kuphryn** · 07-06-2006

while loop correct

Kuphryn

**dwks** · 07-06-2006

There is a reason for that. If you have a #define like this:

Code:

#define swap(x,y) \
    do { \
        int t = x; \
        x = y; \
        y = t; \
    } while(0)

it mandatates a semicolon at the end of the call to swap:

Code:

swap(x, y);

If you just used regular { }, then you could get away with

Code:

swap(x, y)

It's just to make it look more like ordinary C code.

There was a thread about this somewhere a while ago. I can't seem to find it though. If you're interested, look through the search results for "while(0)".

[edit] I found it: http://cboard.cprogramming.com/showthread.php?t=66510 [/edit]

**anonytmouse** · 07-06-2006

This construct is used for macros.

EDIT: Two minutes too late.

**laserlight** · 07-06-2006

That sounds like a really horrible hack in this day and age of templates and generic programming.

**Mario F.** · 07-06-2006

The fact we need to use macros to explain that loop is a sure sign the loop is useless.

**lilhawk2892** · 07-06-2006

i thought that kind of loop wouldnt run unless we had something like

Code:

do 
{
//do whatever
}while(int != 4)

in that kind of format

**laserlight** · 07-06-2006

This is a do while loop, not a while loop.

**Prelude** · 07-06-2006

>The fact we need to use macros to explain that loop is a sure sign the loop is useless.
It's impossible to say without any relevant context. I can think of several ways to justify that code by changing the context.

**dpro** · 07-06-2006

Originally Posted by Prelude

>The fact we need to use macros to explain that loop is a sure sign the loop is useless.
It's impossible to say without any relevant context. I can think of several ways to justify that code by changing the context.

I'd be interested to see that actually. Honestly curious, not being snide

.

**Mario F.** · 07-06-2006

Well, I would also like to see exactly in which context that loop can be useful.

**Prelude** · 07-06-2006

The macro context was already given.

How about a text book or tutorial? Such an example would be a good way to describe the workings of loop conditions in general (with the false condition) and the do..while loop by showing how it always runs once.

What about evolving code where it's likely that the body will become a loop but not quite yet?

What about debugging, where only a single iteration is required?

**dpro** · 07-06-2006

Originally Posted by Prelude

The macro context was already given.

How about a text book or tutorial? Such an example would be a good way to describe the workings of loop conditions in general (with the false condition) and the do..while loop by showing how it always runs once.

Good point, that would be good for a tutorial.

Originally Posted by Prelude

What about evolving code where it's likely that the body will become a loop but not quite yet?

Also a very good point, and thinking about it, I have done this in my own work.

Originally Posted by Prelude

What about debugging, where only a single iteration is required?

I'm a bit wary on this, but I profess I wouldn't think about this either. I would prefer more a simple if statement, but I can see where this has merit in certain applications. Something to think about. Thanks!

**Mario F.** · 07-06-2006

Oh. I thought you were talking about situations in which the code would make sense.

I'm not even sure anymore why we are discussing this... Sure, I agree with you and I can add more... however the truth of the matter is that this is the 14th post on a subject that has only one answer:

That loop is useless. Does nothing.

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