Question

If I want to define a value only if it is not defined, I do something like this :

#ifndef THING
#define THING OTHER_THING
#endif

What if THING is a typedef‘d identifier, and not defined? I would like to do something like this:

#ifntypedef thing_type
typedef uint32_t thing_type
#endif

The issue arose because I wanted to check to see if an external library has already defined the boolean type, but I’d be open to hearing a more general solution.

Answer 1

No there is no such facility in C++ at preprocessing stage. At the max can do is

#ifndef thing_type
#define thing_type uint32_t 
#endif

Though this is not a good coding practice and I don’t suggest it.