Re: strange output

From: richard@xxxxxxxxxxxxxxx (Richard Tobin)
Date: 29 Aug 2006 20:23:38 GMT

In article <44F49C75.8F90E33B@xxxxxxxxx>,
CBFalconer <cbfalconer@xxxxxxxxxxxxx> wrote:

#define swap(a,b) { ..... }

Either:

#define swap(a,b) do {temp=(a); (a)=(b); (b)=temp;} while (0)

Or:

#define swap(a,b) (temp=(a),(a)=(b),(void)(b)=temp)

No. Only the do while (0) method will work in all circumstances.
With the braces you will get errors with:

if (condition) swap(x, y);

because of the terminal semicolon.

You get a problem with the braces, but not with the parenthesised
version.

I disagree.
There's nothing wrong with:

if (condition) (temp=(a),(a)=(b),(void)(b)=temp);

True.

You never follow an "if" with an "else"?

The parenthesised version, with a semicolon, is fine in that case.

The do { } version has the advantage that you can include declarations.

-- Richard

.

References:
- strange output
  - From: dis_is_eagle
- Re: strange output
  - From: CBFalconer
- Re: strange output
  - From: pete
- Re: strange output
  - From: CBFalconer

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