Question

I have 3 classes (it could be 300) , each one with its own header and implementation.
I’d like to write an ‘elegant’ way to organize the way I load of any class needed by every class of the three. Maybe this example helps…

I have : class1 class2 class3

Every header has:

#ifndef CLASS#_H 
#define CLASS#_H   
  #define FORWARD_STYLE
  #include "general.h"
 #endif

Every implementation has:

  #define DIRECT_STYLE
  #include "general.h"

OK
I’m going to write a ‘general.h’ file in which I’d have :

#ifndef DIRECT_STYLE 
#ifndef CLASS1_H
#include "class1.h"
#endif
#ifndef CLASS2_H
#include "class2.h"
#endif
#ifndef CLASS3_H
#include "class3.h"
#endif
#endif

#ifndef FORWARD_STYLE 
class Class1;
class Class2;
class Class3;
#endif

// a lot of other elements needed 
#include <string.h>
#include <stdio.h"
....
#include <vector.h" 
( all the class I need now and in the future )

This is a good structure ? Or I’m doing some idiot thing ?
My goal is having one unique ‘general.h’ file to write all the elemenst I need…
Are this to work fine ?
Thanks

Answer 1

The basic rules to follow are:

1. Let each of your source file include all the header files it needs for getting compiled in a standalone manner. Avoid letting the header files include in the source file indirectly through other files.
2. If you have constructs which will be needed across most source files then put them in a common header and include the header in Only in those source files which need it.
3. Use Forward declarations wherever you can.There are several restrictions of when you can get away using them,read this to know more about those scenarios.

Overall it is a good idea to avoid including unnecessary code in source files through a common header because it just results in code bloat, so try and keep it to a minimum. Including a header just actually copy pastes the entire header to your source file and Including unnecessary files has several disadvantages, namely:

1. Increase in compilation time
2. Pollution of global namespace.
3. Potential clash of preprocessor names.
4. Increase in Binary size(in some cases though not always)