extern a public member of a class - is it possible?

[drwbns]

Hi guys, I was trying to access an object's member I've created in one file, from another file. The problem I think is that the member is a Private Implementation for that class. I've tried to "extern" the member with no luck. So how can I get the object from one class to another? I hope I made this clear enough...


To make things clearer -

//MyClass.h

class MyClass {
public:
class PImpl;
PImpl *p;
}

//MyClass.cpp

class MyClass::PImpl {
     public:
       SomeClass * member;
}

MyClass::MyClass {
p = new PImpl;
p->member = SomeFunction();
}

and I need to access p in another header file, how?

[laserlight]

p is a public member, so as long as you have a MyClass object, you can access its p member.

[drwbns]

I realized that after I posted, thanks for the reply though

[Lindley]

In general, accessing p directly is in contradiction to the pimpl design pattern. Anything within PImpl which you need to access externally should be passed through a method in MyClass.

[drwbns]

when I try to access p such as with -

MyClass *m;

then try to access the member using -

m->p

I get the error pointer to incomplete class type is not allowed. I also tried to add a getPImpl() function that returns p to Myclass, and that won't return p for some reason. Why?

[Paul McKenzie]

when I try to access p such as with -

MyClass *m;

then try to access the member using -

m->p

I get the error pointer to incomplete class type is not allowed.

In whatever context you're using m->p, the compiler needs to know the full definition of class Pimpl. In other words, if the compiler doesn't know what a Pimpl is, you can't access members of unknown types. Forward declarations, as you did in your first post, is only good for pointer and reference declarations, and maybe a scant few other scenarios. So in general, usage of such forward-declared types requires the full definition to be available.

So in your CPP file, just include "pimpl.h", or whatever you called the file that has class Pimpl defined.

Regards,

Paul McKenzie

[Lindley]

How to make it work is beside the point. The primary thing to understand is-----if you need access to p, then the pimpl design pattern is not appropriate. You are not using it correctly if p is exposed anywhere except in the MyClass methods.