Token-pasting operator (##) is eating spaces in my C++ macro

Question

I was having trouble with the following macro, and I found out that the token-pasting operator (##) is eating the space between static and the return type:

#define MY_FUNCTION(aReturnType) static ##aReturnType MyFunction() { }

So the preprocessor was turning this:

MY_FUNCTION(bool)

into this:

staticbool MyFunction() { }

which caused weird compilation errors.

I came up with the idea of putting parentheses around the static keyword:

// This works but is kind of weird
#define MY_FUNCTION(aReturnType) (static) ##aReturnType MyFunction() { }

Are there any better solutions?

Answer 1

I think that your problem is that you don't want to use token pasting here. If you change the macro to

#define MY_FUNCTION(aReturnType) static aReturnType MyFunction() { }

Then if you write

MY_FUNCTION(bool)

it will expand out into

static bool MyFunction() { }

I am assuming that this is what you want to do, since I can't see what you're trying to paste the aReturnType argument to the macro onto.

Hope this helps!

Answer 2

As it should do? You told it to paste together static and bool. If you don't want that and you want static bool instead, then don't paste them together?