How to create an initialised object declared as a class member variable?

C

CFF

I am working on a VC6++ project that involve an object to be initialised
by a 'this' pointer pointing to another object. I encountered, however,
a syntax error. I wonder if someone can help. See the code below. What I
couldn't figure out is it is OK with

CMyClassA B2(this);

in fileB.cpp but a SYNTAX ERROR with

CMyClassA m_B2(this);

in fileB.h. What should I do in order to create a initialised object of
CMyClassA if I really need a class member variable (m_B2) rather than a local (B2)?

Thanks for any help.


/////////////////////////// fileA.h ///////////////////////////
//
// forward declaration
class CMyClassB;

// CMyClassA declaration
class CMyClassA{
public:
CMyClassB* m_ptA;

public:
CMyClassA();
CMyClassA(CMyClassB* ptB);
};


/////////////////////////// fileA.cpp /////////////////////////
//
#include "fileA.h"

// constructor 1
CMyClassA::CMyClassA(void){
// ... whatever ...
}

// constructor 2
CMyClassA::CMyClassA(CMyClassB* ptB){
m_ptA = ptB;
}


/////////////////////////// fileB.h ///////////////////////////
//
#include "fileA.h"

class CMyClassB{
public:
CMyClassA m_B1; // no problem
CMyClassA m_B2(this); // syntax error : 'this', WHY???

public:
CMyClassB(void);
};


/////////////////////////// fileB.cpp //////////////////////////

#include "fileB.h"

CMyClassB::CMyClassB(void){
CMyClassA B1; // no problem
CMyClassA B2(this); // no problem
}


int main(void){
// ... whatever ...
return 1;
}
 
K

kamil

Try this

/////////////////////////// fileB.h ///////////////////////////
//
#include "fileA.h"

class CMyClassB{
public:
CMyClassA m_B1; // no problem
CMyClassA m_B2; // we won't call constructor here

public:
CMyClassB(void);
};


/////////////////////////// fileB.cpp //////////////////////////

#include "fileB.h"

CMyClassB::CMyClassB(void)
: m_B2(this) // we will call it here instead ( hope there is no problem
with passing 'this' pointing to not fully constructed object )
 
K

Karl Heinz Buchegger

CFF said:
/////////////////////////// fileB.h ///////////////////////////
//
#include "fileA.h"

class CMyClassB{
public:
CMyClassA m_B1; // no problem
CMyClassA m_B2(this); // syntax error : 'this', WHY???

Because this is not the way initializations are specified in C++
What you need is a constructor for CMyClassB, which does the initialization


CMyClassB() : m_B2( this ) {}
 
K

Karl Heinz Buchegger

Karl said:
Because this is not the way initializations are specified in C++
What you need is a constructor for CMyClassB, which does the initialization

CMyClassB() : m_B2( this ) {}

Oh. I see you already have a constructor. So add the initialization
to that constructor
 
C

CFF

kamil said:
Try this


with passing 'this' pointing to not fully constructed object )

Thank you for your help. I've tried it out and it works. But ... I am
getting a warning message saying

"warning C4355: 'this' : used in base member initializer list"

when complied. I am a bit worry about this. Any idea about what's the
problem with it? Does it cause any undersirable effect? Thanks again.
 
M

Michael Chisholm

I think as long as you don't try to manipulate the half-constructed
object, you're fine. I believe I do this very thing in some piece of
software I wrote, and I have seen no ill effects. The compiler is just
reminding you... you can always disable the warning with a #pragma.
 

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