结合两个宏？

Question

Following macro MY_SIZE_OF_VARIABLE gives sizeof variables and MY_SIZE_OF_DATATYPE gives size of inbuilt datatype. I want to combine these two macro in one Macro.

#define MY_SIZE_OF_VARIABLE(X) (char *)(&X+1)-(char *)(&X)
#define MY_SIZE_OF_DATATYPE(X) (X*)0 + 1

I tried to combine these but i can't do that.

Answer 1

You can't do that. Part of the evil magic that is preprocessor macros is that it is a simple text replacement with no judgment of syntactic context. This is so that you can do all sorts of wacky stuff like concatenating symbols, lazy evaluations, etc. etc. The other end of that is that you can't turn around and ask it what its parameter is - it's all just text in a macro.

Short of declaring a macro for every symbol in your source , including both types and variables, that consists of the symbol concatenated with __MY_SIZE or something, you really can't do this. You are stuck with a sizeof you didn't write, for better or worse.