Question

I was looking at some coding done in a header file of a program installed on my PC & i found this :

# define A( CLASS )                                                  \
B(CLASS)                                                             \
void                *D(const C*to);

can anybody tell me what this means?
what are those slashes for & why hasnt all of this written in 1 line?
what does (CLASS) mean over here?
& why is there so much spacing done?

Answer 1

The backslashes are there to “protect” the newline — the preprocessor will throw away both the \ and the newline when reading in the file, putting the entire thing on one logical line. (Well, it’ll also emit #line markups so the compiler can generate decent error messages too.)

Someone thought that layout was more legible than this:

#define A(CLASS) B(CLASS) void *D(const C*to);

If you imagine that B, D, and C are probably replaced with something else in the file, it’ll look a bit like this in the output:

Monkey(Simian) void *Bananas(const sticks *to);

It must have made more sense to them, as they wrote the macro, to instead “see” it like this:

Monkey(Simian)
void          *Bananas(const sticks *to);

I’m not sure it is an improvement (and I think I hate the style), but hopefully it makes sense now.