C++ using private and public in macro, inside class

Question

Im trying to make a macro for padding my classes which i use in game hacking. Let me show you what i am trying to do:

#define pad(loc, size)  private: \
                    char _pad#loc[#size]; \
                    public:

then i want to use it like:

class C_VTable {
public:
   float member;          // <- public
   pad(0x4, 0x30);        // <- private im not sure how to make the pad name be like pad0x4
   float anothermember;   // <- public again
};

How can i do this, because i get an error saying it expected a ; a little messy, but i hope you understand.

Any help is greatly appreciated :)

`#` creates a string literal, use `##` to glue `__pad` and `log` together — Patrik H, Aug 17 '16 at 18:27
Identifiers with a double underscore are reserved. See http://stackoverflow.com/q/228783/10077. — Fred Larson, Aug 17 '16 at 18:36
When debugging macro problems, it sometimes helps to look at the output of the preprocessor to see what it did with your macro. Every compiler I know of has an option to run just the preprocessor. It's usually a variant of -E. — Pete Becker, Aug 17 '16 at 19:08

score 4 · Accepted Answer · answered Aug 17 '16 at 18:26

4

Use the ## paste operator to combine two tokens together. Also, don't stringify the size using # - you don't want a string inside the square brackets.

#define pad(loc, size)  private: \
                    char __pad##loc[size]; \
                    public:

answered Aug 17 '16 at 18:26

aschepler

70,891
9
107
161

Thank you very much. Another question, if i do pad( 0x7AE, 2 ) is the pad name going to be __pad0x7AE[2], __pad7AE[2] or __pad1966[2] (7AEh)? – Ranarrr Aug 17 '16 at 18:30
The field name will be `__pad0x7AE`. The token gets pasted raw just as you spelled it. – aschepler Aug 17 '16 at 18:33

C++ using private and public in macro, inside class

1 Answers1