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

The solution I ended up using was including stdbool.h. I know this doesn't solve the question of how to check if a typedef is already defined, but it does let me ensure that the boolean type is defined.