Re: OFFTOPIC: 'do { ... } while (0)?'

David Schwartz (davids@webmaster.com)
Tue, 14 Apr 1998 14:53:13 -0400

>Why are so many macros written as: do { ... } while (0) rather than
>as simply { ... } ?

Because of the semantics of what a semicolon after it means. Consider:

#define FOO1(a) do { baz(a); bar(); } while(0)
#define FOO2(a) { baz(a); bar(); }

if(x==1) FOO1(1); else FOO1(1);
if(x==1) FOO2(1); else FOO2(2);

See? Both look like they should work, but only FOO1 actually does.

DS

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