How to include part of file by C++ preprocessor #include

Question

I want to refer some stable library code which is not maintained by me. Actually it is some MFC code snippet.

But, whenever I want to include the code snippet, I have to #include entire file, which consequently I have to include other stuff, then the whole MFC ... The consequence is not acceptable.

Currently, I copy/paste the code snippet into my project, but I feel disgraceful. Can I just refer part of a file by C++ preprocessor?

Even the code is hard-linked with specific MFC version, it is better than duplicate them in my project. With such hard-link, I will know it's from MFC and save my time to check them.

Is there some super #include usage?

Can we write something like

#include  "foo.h" line [12, 55)

which means to include line 22 to 54 for foo.h

Yes - 1) you can "block out" the parts of the header you don't want with "#ifdef/#ifndef/#endif". Of course that means modifying the header. 2) Alternatively, you can cut/paste the parts you want into a new header. — paulsm4
– paulsm4, Commented Jan 22, 2013 at 7:26
It will probably work out cleanest, IMO, if you create a header of your own and copy the snippet into that, once per version of MFC, and then use your header. Not particularly nice, but better than hacking a system-supplied header (that is very much a last resort). — Jonathan Leffler
– Jonathan Leffler, Commented Jan 22, 2013 at 7:39
You are talking about to include header stuff, aren't you? Or should it be you are trying to include any sorts of implementing code? For the latter: Do not do that, but build an object to link to. — alk
– alk, Commented Jan 22, 2013 at 7:47
Fiddling with compiler headers is a bad idea for many reasons. But apart from that, it doesn't seem like a particularly bright idea to refer to a header file for the sake that it is maintained by someone else, then make sure that you have to manually edit said header file for it to work. — Lundin
– Lundin, Commented Jan 22, 2013 at 7:48

dutt · Accepted Answer · 2013-01-22 07:32:47Z

7

What some have done is write #ifdef-sections in their headers to allow including files to only get specific parts. I don't know if your MFC file has those but you can look through it and use any existing ones or write your own.

The header usually look something like this

#ifdef USE_FANCYPANTS
bool hasFancyPants();
#endif

#ifdef USE_COOLSTUFF
void doCoolStuff();
#endif

And your include files then use #define before including.

#define USE_FANCYPANTS
#include "header.hpp"

Then you only get hasFancyPants() and not doCoolStuff()

answered Jan 22, 2013 at 7:32

dutt

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Ajay · Accepted Answer · 2013-01-22 08:22:16Z

0

You can use conditional compilation to inlcude/exclude stuff you dont need. You have to change the source code slighty, and amend project settings.
Can use typedef keyword, which would define types differently for MFC and non-MFC, and/or specific to your project settings, and the legacy code.
You may put entire stuff in a DLL or a .LIB (having code, not just declaration), and put the linker pragma in header file itself.

answered Jan 22, 2013 at 8:22

Ajay

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