On Mar 10, 2008, at 7:03 PM, sergio masci wrote:

> Could you please explain what you meen by "making a multi-line macro
> safe". I have never seen this contruct used to protect code.

A macro that contains multiple lines of code is not "safe" to use in
assorted places, for example, to avoid compiler warnings, I convert  
all my old
macro definitions:
	#define CHECK_ERR if (errcode = get_error()) {print_error(errcode)}
to	#define CHECK_ERR errcode = get_error(); if (errcode) {print_error 
(errcode)}

that's all very nice, but the macro now fails in cases like:
	if (suspiciousstuff)
	    CHECK_ERR;
	else
	   /* everything peachy keen. */

(It's VERY similar to the problem you get using assembly macros that can
expand to more than one instruction after SKIP instructions.)

A common way to fix this in C is to make your macro a block statement  
that
executes exactly once:
	#define CHECK_ERR do { \
                 errcode = get_error(); \
                  if (errcode) {  \
                     print_error(errcode) \
		} while (0)
Now, not matter how complex the code inside the do ... while  
statement, it
it lexes/parses the same as a single C statement.

BillW

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