Question

I think the preprocessor handles files one by one and I can’t figure out how to do it with includes, so I think it’s impossible, but it would be great to hear other’s thoughts.

I have in a.cpp:

#define A 1

and I want to use it from 2.cpp.

EDIT:
I cant modify first file. So for now i just have copied defines. But question still opened.

Answer 1

Defines inside a source file aren’t seen by other translation units. Implementation files are compiled separately.

You can either

• put them in a header and include it
• use your compiler’s options
• do it the sane way – extern const int A = 1; in an implementation file and declare it when you want to use it extern const int A;.

Of these, I’d say the first option is possibly the worst you can use.