Question

I’m trying to get the pre-processor to generate a list based on which names have been defined. Something like this

#define LIST "Start of list!"

#ifdef WITH_FOO
#define LIST LIST "Foo"
#endif

#ifdef WITH_BAR
#define LIST LIST "Bar"
#endif

#define LIST LIST "End of list!"

I get some warnings from this about LIST being redefined, and then later in the code where I try to use the LIST it gives an error: “LIST was not declared in this scope” which, warnings aside, I believe it should be.

How can I get this to work?

Answer 1

You could use some auxiliary macros:

#ifdef WITH_FOO
#  define LIST_FOO "Foo"
#else
#  define LIST_FOO
#endif

// ... ditto for BAR

#define FOO "Start of list!" LIST_FOO LIST_BAR "End of list!"