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From: Giovanni Dicanio on 26 Apr 2008 17:25

"Z.K." <nospam(a)nospam.net> ha scritto nel messaggio
news:eUv3Bo9pIHA.4884(a)TK2MSFTNGP06.phx.gbl...

> The class forward technique is kind of new to me and I have never really
> understood it that well. I don't remember reading of such a thing in any
> of my text books, but I will review them to be sure.

The concept is simple: by using a forward declaration, you are telling the
compiler that e.g. the class that you are forward-declaring is defined
somewhere else in code.

// FILE: X.h
// DESC: Header file for class X

// Forward declaration
// Tells the compiler that class Y is defined somewhere else...
class Y;

class X
{
....

private:
Y * pY; // Y class is forward declared
};

Considering that a pointer (like "Y* ") is 4 bytes on 32 bits architectures,
even if the compiler does not know the exact size of the class you are
forward-declaring, the compiler certainly can alloc a slot of 4 bytes inside
class X to store the pointer to that Y class.

HTH,
Giovanni



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