[computer-go] C++: #include vs .h files

[Weston Markham]

You can "forward declare" one (or both) of the classes in the header
for the other:

in BitBoard.h:

class BoardState;
class BitBoard {
    BoardState* state_;
};

... the catch is that when the forward-declared class is mentioned in
that header file, the type is not "complete", which basically means
that the compiler does not know its size.  If the class being defined
declares storage for the forward-declared one, you will have problems.
 But of course, this sort of relationship could not be circular
anyway, so you can usually resolve such issues:

struct Foo;
struct Bar;
struct Foo {
    Bar bar;  // not legal, because Bar's size is not known.
};
struct Bar {
    Foo foo; // also not legal, and at this point, each structure must
recursively contain itself!
};

Weston

On 8/9/06, Peter Drake <drake at lclark.edu> wrote:
>
> That mostly worked, but I have a more subtle problem.
>
> I have two classes, BitBoard and BoardState. Each needs to know about the
> other because the other appears in field declarations or method signatures.
> If I put
>
> #include "BoardState.h"
>
> in BitBoard.h and vice versa, there is obviously a circularity. How to get
> around this?
>
>
>
> Peter Drake
> Assistant Professor of Computer Science
> Lewis & Clark College
> http://www.lclark.edu/~drake/
>
>
>
>
>
> On Aug 9, 2006, at 3:02 PM, Peter Drake wrote:
> Okay, I'll try cleansing my .h files of definitions. Stay tuned.
>
> (Is it okay to declare object fields in .h files?)
>
>
> Peter Drake
> Assistant Professor of Computer Science
> Lewis & Clark College
> http://www.lclark.edu/~drake/
>
>
>
>
>
> On Aug 9, 2006, at 2:55 PM, Weston Markham wrote:
>
> Most likely, you have a definition in a .h file.  This can be legal,
> but you may need to mark it "inline".  Any chance you can post a
> concise example?  (what minimal declarations & definitions in which
> files will demonstrate the problem)
>
> Weston
>
> On 8/9/06, Peter Drake <drake at lclark.edu> wrote:
>
> Thanks for the quick response on the array passing. I think I get it now.
>
> I'm having a devil of a time trying to divide my classes between .h and .cpp
> files. Specifically, if I have the same #include in several .cpp files, I
> get complaints about redundant definitions from the linker. I can avoid this
> by putting everything in the .h files (except for one .cpp file), but then I
> can't define classes that depend on each other.
>
> Any advice?
>
>
> Peter Drake
> Assistant Professor of Computer Science
> Lewis & Clark College
> http://www.lclark.edu/~drake/
>
>
>
>
>
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