Error when using other class' object as argument

**renanmzmendes** · 02-18-2008

Hi,

Thanks for your replies, people.

Each class does use the other, having functions with the other class' objects as arguments.

I've read through your answers but I haven't quite understood how the whole forward declaration works. Can someone elaborate a little bit more for me? Thanks.

**laserlight** · 02-18-2008

I've read through your answers but I haven't quite understood how the whole forward declaration works. Can someone elaborate a little bit more for me? Thanks.

This would be a forward declaration of B followed by a definition of A where A has a member pointer to B:

Code:

class B;

class A
{
public:
    // ...
private:
    B* b;
};

The idea is that A does not need the definition of B since it only uses a pointer (or a reference) to B. It also allows one to include A's header in B's header if B's definition depends on A and needs A's definition.

**renanmzmendes** · 02-18-2008

Thanks, laserlight. That indeed did the trick. I've just declared class B in class A's definition and vice-versa and I was able to compile my application. Thanks again.

Renan M Z Mendes

**Elysia** · 02-19-2008

Just remember that it will only work if class A uses a pointer or reference to B.

Code:

class B;

class A
{
public:
	// ...
private:
	B* pb; // works
	B& rb; // works
	B bb; // doesn't work
};

**renanmzmendes** · 02-19-2008

Actually, I'm not using a B (or A) object as a class member. I'm justing using it as an argument in a member function of the other class. But I'll keep that in mind for future situations. Thanks.

Renan M Z Mendes

**Elysia** · 02-19-2008

It's the same for both arguments and member variables, so no worries there.

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