Exclude line from compilation via Makro C++

Question

I've got some problem, which might be simple to solve.

I have code like this:

#define _MG_ALL //This might be defined in some other headerfile

#ifndef _MG_ALL
#define MG_ALL <?????>
#else
#define MG_ALL <nothing>
#endif

In the code it is used like this:

ALL foo = thisIsSomeFunc(foo);

This line should only be compiled, if _ALL is defined. This could also be solved by using this:

#ifdef ALL
    foo = thisIsSomeFunc(int foo);
#endif

But I would prefer just one short macro in the same line.

I've just read [here](http://stackoverflow.com/q/1510869/4711812) that comment stripping is done before macro expension is performed... — muXXmit2X, Sep 20 '16 at 11:40

score 3 · Accepted Answer · answered Sep 20 '16 at 12:19

What you could do is defining the macro like so:

#ifdef _ALL
#define ALL if(1)
#else
#define ALL if(0)
#endif

When you use it this it will produce code similar to this

ALL std::cout << "Debug Message" << std::endl;
 ==> if(1) std::cout << "Debug Message" << std::endl;

A good compiler should recognize the constant value in the if-statement and should only compile the right part (1 ==> if part, 0 ==> nothing).

1 Answers1