C macro get typeof argument

Question

I am trying to write a macro to assist with object oriented programming in C. As I store the class information in a constant struct, I need to create a macro that does the following:

• Take the type of the object (typeof the derefenced pointer)
• Append _info to get the name of the desired classInfo struct
• Take the address of that symbol so it can be passed to the function
• Call the destroyObject function with a pointer to the class struct and the object itself

An example:

queue_t* p = NULL;
delete(p);

delete should expand to:

destroyObject(&(queue_t_info), p);

I tried using this macro, but I can't get to to work:

#define delete(X) (destroyObject(&(typeof(*X)##_info), X))

I'm having trouble with the typeof part to work correctly.

Answer 1

typeof isn't macro, it is language construction and it is expanded by compiler, not preprocessor. Since preprocessing goes before compilation, macro can't access typeof result.

Your delete(p) is expanded to: (destroyObject(&(typeof(*p)_info), p)). (You can see it by -E gcc flag)