two classes #including each other

[stefven blonqhern]

hi, i imagine we've all seen this one posted before but i can't get
any solutions to work for me.. for example:

i have two classes MyClass and Shape. MyClass creates Shapes (and
derived classes from Shape) and it also wants to pass a pointer to
itself to a member function of Shape so that it can access MyClass'
members. Pseudo code example:

class MyClass {

void MyFunction{
aShape->DoSomethingToShape(this)
}

private:

Shape* aShape;
}

/////////////

class MyClass; // forward declaration

class Shape { // is a base class

void DoSomethingToShape(MyClass* aClass) {
aClass->some_member; // ** ERROR invalid use of undefined type
'struct MyClass' **
}

I have simplified greatly (possibly too much to make proper sense).
Really i'm trying to avoid passing 10-20 references to MyClass members
because it feels a bit clumsy. I just want to pass a pointer to a
MyClass so that Shape can access what it wants.

Is there a better way?

thanks, stefven.

[Neelesh Bodas]

On Aug 24, 9:47 pm, stefven blonqhern <[e-mail]>
wrote:

hi, i imagine we've all seen this one posted before but i can't get
any solutions to work for me.. for example:

i have two classes MyClass and Shape. MyClass creates Shapes (and
derived classes from Shape) and it also wants to pass a pointer to
itself to a member function of Shape so that it can access MyClass'
members. Pseudo code example:

class MyClass {

void MyFunction{
aShape->DoSomethingToShape(this)

}

private:

Shape* aShape;

}

/////////////

class MyClass; // forward declaration

class Shape { // is a base class

void DoSomethingToShape(MyClass* aClass) {
aClass->some_member; // ** ERROR invalid use of undefined type

myClass needs to be defined before its members are used.

'struct MyClass' **

}

I have simplified greatly (possibly too much to make proper sense).
Really i'm trying to avoid passing 10-20 references to MyClass members
because it feels a bit clumsy. I just want to pass a pointer to a
MyClass so that Shape can access what it wants.

You can do something like this: (just an example):

//Myclass.h
class Myclass
{
public:
void foo();
};
//Myclass.cpp
#include "Myclass.h"
void Myclass::foo()
{
...
}
//shape.h
class Myclass;
class Shape
{
public:
void DoSomethingToShape(Myclass*);
};
//shape.cpp
#include "shape.h"
#include "myclass.h"

void Shape::DoSomethingToShape(Myclass* aClass)
{
aClass->foo();
}
-N

[Victor Bazarov]

stefven blonqhern wrote:

hi, i imagine we've all seen this one posted before but i can't get
any solutions to work for me.. for example:

i have two classes MyClass and Shape. MyClass creates Shapes (and
derived classes from Shape) and it also wants to pass a pointer to
itself to a member function of Shape so that it can access MyClass'
members. Pseudo code example:

class MyClass {

void MyFunction{
aShape->DoSomethingToShape(this)
}

private:

Shape* aShape;
}

/////////////

class MyClass; // forward declaration

class Shape { // is a base class

void DoSomethingToShape(MyClass* aClass) {
aClass->some_member; // ** ERROR invalid use of undefined type
'struct MyClass' **
}

Pull this function's definition out of the class 'Shape' and
#include <MyClass.hright in front of it (if you need this to be
in the header). Or just place it in a separate translation unit.

I have simplified greatly (possibly too much to make proper sense).
Really i'm trying to avoid passing 10-20 references to MyClass members
because it feels a bit clumsy. I just want to pass a pointer to a
MyClass so that Shape can access what it wants.

Is there a better way?

Usually, yes. The Java habit of having all functions implemented in
the class definition is not the best to follow when C++ is concerned.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[stefven blonqhern]

okay, thanks for the replies.. naturally i forgot to mention that i'm
using public inheritance. Shape being the base class and all member
functions are virtual.

looks like i have some thinking to do, thanks,
stefven.

[stefven blonqhern]

Is there a better way?

>
Usually, yes. The Java habit of having all functions implemented in
the class definition is not the best to follow when C++ is concerned.

so really i should be separating the interface and the
implementation. Java? never heard of it!

Stefven

[Victor Bazarov]

stefven blonqhern wrote:

>>Is there a better way?

Usually, yes. The Java habit of having all functions implemented in
the class definition is not the best to follow when C++ is concerned.

so really i should be separating the interface and the
implementation. Java? never heard of it!

Interface and implemenatation are concepts, they are separate by
nature. You should be separating declarations and definitions.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask