Why won't this compile and how can it be implemented so that it does?

Question

Here is some C++ code I\'m playing around with:

#include 
#include 

#define IN ,
#define FOREACH(x,y) for(unsigned int i=0;i&l         


        

Answer 1

Others have already explained why it doesn't compile as is.

In order to make it work you have to give that IN a chance to turn into a comma. For that you can introduce an extra level of "indirection" in your macro definition

#define IN , 
#define FOREACH_(x,y) for(unsigned int i=0;i

In this case you'll have to use some substitute for comma (like your IN) and can no longer specify comma explicitly. I.e. now this

FOREACH(int item IN ints) 
    cout << item; 
ENDFOREACH 

compiles fine, while

FOREACH(int item, ints) 
    cout << item; 
ENDFOREACH 

does not.