Empty function macros

c++ function macros compilation
Qix - MONICA WAS MISTREATED picture Qix - MONICA WAS MISTREATED · Feb 8, 2012 · Viewed 31.6k times · Source

If I define a function macro with no actual body, is it like an empty string with the compiler (i.e. It doesn't generate any extra instructions at compile time)?

Example:

#define SomeMacro(a)

SomeMacro("hello"); // This line doesn't add any instructions, does it?

Answer

Mark Ransom picture Mark Ransom · Feb 8, 2012

You're absolutely correct, the empty macro doesn't generate any code.

I've seen two places where this is useful. The first is to eliminate warnings when a function parameter isn't used:

#define UNUSED(x)

int foo(int UNUSED(value))
{
    return 42;
}

The second is when you use conditionals to determine if there should be code or not.

#ifdef LOGGING_ENABLED
#define LOG(x) log_message(x)
#else
#define LOG(x)
#endif

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