Using Macros

[Richard A. O'Keefe]

In article <14339 at shlump.nac.dec.com>, farrell at onedge.enet.dec.com (Bernard Farrell) writes:
> In article <362.26be9dcc at astro.pc.ab.com>, yoke at astro.pc.ab.com (Michael Yoke) writes...
  [asks about defining macros that expand to more than one statement]

> 	};
> 
> The presence of an empty statement after
> the closing brace should not cause any problems,

I wasn't going to reply to this, but the Official Free Answer[*] is
to use the expansion
	do { /* your statements go here */ } while (0)
This will work in any context where a statement is allowed; it wants
a semi-colon after it just like a simple function call would.  For
example:
	#define swap(Type,x,y) do { \
	    Type *ZZQ1 = &(x); \
	    Type *ZZQ2 = &(y); \
	    Type  ZZQ3 = *ZZQ1; \
	    *ZZQ1 = *ZZQ2; *ZZQ2 = ZZQ3; \
	} while (0)

(Exercise for the reader:  why did I write 3 declarations instead of 1?)

[*] An Official Free Answer is something you find in an FSF manual,
    such as the manual for CCCP.
-- 
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