Using Macros

[Stephen Clamage]

gg10 at prism.gatech.EDU (GALLOWAY) writes:
>Why doesn't this work?

>#define A_MACRO(bar, baz)  func1(bar), func2(baz)

>I have been using syntax like this for awhile, is this wrong or unportable?

You need an extra set of parens:
	#define A_MACRO(bar, baz)  ( func1(bar), func2(baz) )
Look what happens without the parens:
	i = A_MACRO(3, 4) + 2;
becomes:
	i = func1(3), func2(4) + 2;
which is the same as
	(i = func1(3)), (func2(4) + 2);
which is probably not what was meant.  With parens, it becomes;
	i = (func1(3), func2(4)) + 2;
which may or may not be what was meant, but at least the +2 is not discarded.

If the do { ... } while(0) construct was used instead, the above
expression becomes illegal, which may or may not be what was intended.
-- 

Steve Clamage, TauMetric Corp, steve at taumet.com