Question

My assert macro is like this:

#ifdef DEBUG
#define ASSERT(x) ((void)(!(x) && assert_handler(#x, __FILE__, __LINE__) && (exit(-1), 1)))
#else 
#define ASSERT(x) ((void)sizeof(x))

I thought this was more or less bulletproof but I seem to be using it a lot in the context of asserting the return value of functions which are important for their side effects. If in my release build I end up compiling

ASSERT(fgets(buffer,sizeof(buffer)/sizeof(buffer[0]),file));

which would become

((void)sizeof(fgets(buffer,sizeof(buffer)/sizeof(buffer[0]),file)));

Is there a chance this will get completely optimized out? I am fairly certain that it won’t (I’m calling a function, fgets), but what exactly is the condition that assures it? Are there any operations with side effects which the optimizer might throw out?

Answer 1

The usual meaning of assert is to be optimized out, so it might be better to stick to those semantics and do

#else 
#define ASSERT(x)
#endif

If you insist on it not being optimized out, why not just do

#else 
#define ASSERT(x) ((void)(x))
#endif

?