typedef 如何在内部工作（在编译器级别）？

Question

i come across this question in an interview recently. they asked me when we create new user defined Type using Typedef (Like typedef unsigned char CHAR) what happens internally??

Answer 1

Internally there will happen nothing because it is only the information for the compiler that you introduced some alias for another type.

According to the C Standard (6.7.8 Type definitions)

3. ...A typedef declaration does not introduce a new type, only a synonym for the type so specified.

Take into account that opposite to C++ in C there is no such a notion as the user defined type. The C Standard does not use such a term.

To define a user type you have to specify its behaviour. The C language does not allow to specify behaviours of types.:)

As for the "memory level" then the only consequence is that you can forget what actual type this typedef alias denotes.:)