Variadic UNUSED function/macro

Question

A well-known and portable way to suppress C compiler warnings about unused variables is (see unused parameter warnings in C code):

#define UNUSED(x) (void)(x)
         


        

Answer 1

What do you think about this:

#define UNUSED(...) [__VA_ARGS__](){};

Example:

void f(int a, char* b, long d)
{
    UNUSED(a, b, d);
}

Should be expanded ad a lambdas definition:

[a,b,d](){}; //optimized by compiler (I hope!)

===== Tested with http://gcc.godbolt.org ===== I've tryed with this code:

#define UNUSED(...) [__VA_ARGS__](){};

int square(int num, float a) {
  UNUSED(a);
  return num * num;
}

The resulting output (compiled with -O0 -Wall) is:

square(int, float):
    pushq   %rbp
    movq    %rsp, %rbp
    movl    %edi, -4(%rbp)
    movss   %xmm0, -8(%rbp)
    movl    -4(%rbp), %eax
    imull   -4(%rbp), %eax
    popq    %rbp
    ret

EDIT:

If you can use C++11 this could be a better solution :

template 
void UNUSED(Args&& ...args)
{
    (void)(sizeof...(args));
}