In C/C++, is there a directive similar to #ifndef for typedefs?

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

Answer 1

This might not directly answer the question, but serve as a possible solution to your problem.

Why not try something like this?

#define DEFAULT_TYPE int // just for argument's sake
#ifndef MY_COOL_TYPE
     #define MY_COOL_TYPE DEFAULT_TYPE
#endif
typedef MY_COOL_TYPE My_Cool_Datatype_t;

Then if you want to customize the type, you can either define MY_COOL_TYPE somewhere above this (like in a "configure" header that is included at the top of this header) or pass it as a command line argument when compiling (as far as I know you can do this with GCC and LLVM, maybe others, too).