Is there a C macro, a GCC directive or pragma, to consume the next code statement following the macro, without explicitly passing it as an argument to the macro?
Something like this:
#define CONSUME_NEXT_IF(a) if (a) { (<next>) } else;
And I would use it as:
CONSUME_NEXT_IF(a) stmt1;
And expect it to expand to:
if (a) stmt1;
else;
I am using an if statement here just as an example. The conditional statement isn't the point, rather the ability to consume stmt1 by the macro without actually passing it as an argument.
#define CONSUME_NEXT_IF(a) if (!(a)) {} else
will achieve the effect of only executing the "next statement" (between use of the macro and next ;) if a is true (or non-zero). If you have suitable constraints on what type of expression a is, you might be able to remove the () on (a).
Personally, although you've explained in comments that you want a similar effect to annotations, I consider this will introduce more maintenance concerns - including code obfuscation - than it alleviates. Particularly if it interacts with other macros being used in a or stmt1.
And, of course, it would be necessary to modify your "large code base" to use the macro.
This also leaves dead code in your executable - it doesn't stop code for stmt1 being emitted to the executable (unless a has a fixed compile-time value, and your compiler has capability to detect and optimise code in such circumstances). Therefore such a construct will mean you cannot satisfy requirements of several assurance standards that require prevention of dead code.