How do i separate a class definition into 2 header files?

Question

I need to split one class (.h file)

#ifndef _L_H
#define _L_H
template<class L> class Myclass{
public:
  L();
  firstoperator(..);
  secondoperator(..);
private:
 ...
}
template <class L> Myclass<L>::L() ...
template <class L> Myclass<L>::firstoperator(..) ...
template <class L> Myclass<L>::secondoperator(..) ...

in two different .h file in the following form:

#ifndef _L_H
#define _L_H
template<class L> class Myclass{
public:
  L();
  firstoperator(..);
private:
 ...
}
template <class L> Myclass<L>::L() ...
template <class L> Myclass<L>::firstoperator(..) ...

#ifndef _L_H
#define _L_H
template<class L> class Myclass{
public:
  secondoperator(..);
}

template <class L> Myclass<L>::secondoperator(..) ...

how can I do it correctly without conflict?

Thank you in advance.

You can not split declaration on class into to header files. Although you can split definition into multiple files but thats not a good idea. — Hemant Gangwar, Sep 23 '14 at 17:27

score 16 · Answer 1 · answered Sep 23 '14 at 17:44

16

You can technically do it, but it's ugly. Don't do it.

Class1.hpp:

class MyClass
{
    int something;
    int somethingElse;

Class2.hpp:

    int somethingBig;
    int somethingSmall;
};

I hope it's clear how disgusting that is :)

answered Sep 23 '14 at 17:44

tenfour

36,141
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8

+1 for the 'hacker' thinking. And +1 for probably breaking IntelliSense, and all other such things :P – MicroVirus Sep 23 '14 at 22:11
1

IntelliSense suck with C++ projects that needs kind splitting anyway. – Coldsteel48 Nov 14 '17 at 12:22
1

This feels like the worst practice of all time for any project size. But so smart! Tip of the hat, Sir – NicoBerrogorry Apr 15 '18 at 02:17

score 5 · Answer 2 · answered Sep 23 '14 at 17:27

"how can I do it correctly without conflict?"

You can't. It's not possible in c++ to spread a class declaration over several header files (unlike as with c#). The declarations of all class members must appear within the class declaration body, at a single point seen in each translation unit that uses the class.

You can separate template specializations or implementation to separate header's though.

score 5 · Accepted Answer · answered Sep 23 '14 at 17:39

5

You can use heritage to split class to two headers.

You can declare half class on the base and the other half on the derived.

like this:

class C12{
public:
  void f1();
  void f2();
};

can be splitted to C1 and C12

class C1{
public:
  void f1();
};

class C12: public C1{
public:
  void f2();
};

now C12 is the same as before but splitted to 2 files.

answered Sep 23 '14 at 17:39

SHR

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This may have unwanted side effects. If so, mentioning/recommending [mixins](http://stackoverflow.com/questions/7085265/what-is-c-mixin-style) would have been a better choice. – πάντα ῥεῖ Sep 23 '14 at 17:49
@πάνταῥεῖ That SO question you linked says mixins in C++ are through inheritance (unless I misread it), so I don't see how this answer is different from mentioning mixins? – MicroVirus Sep 23 '14 at 22:13
1

@MicroVirus The [`template`](http://stackoverflow.com/questions/7085265/what-is-c-mixin-style/7087257#7087257) actually makes a big difference! – πάντα ῥεῖ Sep 23 '14 at 22:17

How do i separate a class definition into 2 header files?

3 Answers3