C / C++ / MFC

George_George wrote:

http://msdn2.microsoft.com/en-us/library/wcz57btd.aspx#Mtps_DropDownFilterText

CPallini wrote:

the need of an offset to rearrange things

class A
{
	int a;
public:
	A(){a=0;}
	virtual int do_things(int a){this->a = a; return 0;}
};

class AB: public A
{
	int ab;
public:
	AB(){ab=1;}
	virtual int do_things(int a){A::do_things(a);this->ab = a+1; return 1;}

};

class AC: public A
{
	int ac;
public:
	AC(){ac=2;}
	virtual int do_things(int a){A::do_things(a);this->ac = a+2; return 2;}

};

class ABAC: public AB, public AC
{
	int abac;
public:
	ABAC(){abac = 4;} 
	virtual int do_things(int a){AB::do_things(a);AC::do_things(a);this->abac = a+4; return 4;}
};

int main()
{
ABAC abac;
}

-		abac	{abac=4 }	ABAC
-		AB	{ab=1 }	AB
-		A	{a=0 }	A
-		__vfptr	0x0041574c const ABAC::`vftable'{for `AB'}	*
		[0]	0x00411136 ABAC::do_things(int)	*
		a	0	int
		ab	1	int
-		AC	{ac=2 }	AC
-		A	{a=0 }	A
-		__vfptr	0x00415740 const ABAC::`vftable'{for `AC'}	*
		[0]	0x0041111d [thunk]:ABAC::do_things`adjustor{12}' (int)	*
		a	0	int
		ac	2	int
		abac	4	int

CPallini wrote:

__vfptr 0x0041574c const ABAC::`vftable'{for `AB'} *

CPallini wrote:

[0] 0x00411136 ABAC::do_things(int) *

George_George wrote:

This line means the address of __vfptr pointer is 0x0041574c? Or the value of __vfptr pointer is 0x0041574c?

George_George wrote:

This line means the address of __vfptr[0] pointer is 0x00411136? Or the value of __vfptr[0] is 0x00411136?

__vfptr	0x0041574c const ABAC::`vftable'{for `AB'}	*
__vfptr	0x00415740 const ABAC::`vftable'{for `AC'}	*

__vfptr	0x0041574c const ABAC::`vftable'{for `AB'}	*
[0]	0x00411136 ABAC::do_things(int)	*

George_George wrote:

1.

I noticed that the __vfptr array in AB and in AC are different (0x0041574c and 0x00415740), means the vtable for AB and AC sub-object are different?

George_George wrote:

In my understanding, __vfptr is an array of function pointers. [0] is the value of the 1st function pointer in vtable, right?

So, 0x00411136 means function ABAC::do_things(int) resides in address 0x00411136?

George_George wrote:

1.

I think it means at location 0x0041111d, there is a place holder function, [thunk]:ABAC::do_things, and its job is simply redirect calls the vtable entry in AB, right?

George_George wrote:

2.

--------------------
the offset (equalt to 12 decimal, 0xC hex) needed to align vftable'{for `AC'} to ::`vftable'{for `AB'} (0x00415740 + 0x0000000c = 0x0041574c).
--------------------

I am interested in the function align. Is it a MSVC built-in private function? How do you know the align rule of the align source and align destination? -- Which in this case align vftable'{for `AC'} to ::`vftable'{for `AB'}, why it does not align from something else to something else?

CPallini wrote:

I think it simply contains the adjustor field, i.e. the offset to the AB vtable.

George_George wrote:

1.

CPallini wrote:
I think it simply contains the adjustor field, i.e. the offset to the AB vtable.



So, the adjustor field also takes memory address? Which is at location 0x0041111d?

George_George wrote:

2.

I have studied the link, looks cool. So, after the adjust, the entry [0] for vtable for AC will be, 0x00415740 + 0x0000000c = 0x0041574c, which is address for vtable for AB.

I am wondering what compiler will do next after the adjustment? Translate 0x00415740[0] to 0x0041574c[0] for the function pointer?

#include <iostream>

using namespace std;

class A
{
	int a;public:	A(){a=0;}	
	virtual int do_things(int a){this->a = a; return 0;}
};

class AB: virtual public A
{	
	int ab;
public:
	AB(){ab=1;}
	virtual int do_things(int a){A::do_things(a);this->ab = a+1; return 1;}
};

class AC: virtual public A
{
	int ac;
public:	
	AC(){ac=2;}
	virtual int do_things(int a){A::do_things(a);this->ac = a+2; return 2;}
};

class ABAC: public AB, public AC
{
	int abac;
public:
	ABAC(){abac = 4;}
	virtual int do_things(int a){AB::do_things(a);AC::do_things(a);this->abac = a+4; return 4;}
};

int main()
{
	ABAC abac;

	return 0;
}

#include <iostream>

using namespace std;

class A
{
	int a;public:	A(){a=0;}	
	virtual int do_things(int a){this->a = a; return 0;}
};

class AB: virtual public A
{	
	int ab;
public:
	AB(){ab=1; A * pA = this; pA->do_things(1);}
	virtual int do_things(int a){A::do_things(a);this->ab = a+1; return 1;}
};

class AC: virtual public A
{
	int ac;
public:	
	AC(){ac=2; A * pA = this; pA->do_things(2);}
	virtual int do_things(int a){A::do_things(a);this->ac = a+2; return 2;}
};

class ABAC: public AB, public AC
{
	int abac;
public:
	ABAC(){abac = 4;}
	virtual int do_things(int a){AB::do_things(a);AC::do_things(a);this->abac = a+4; return 4;}
};

int main()
{
	ABAC abac;

	return 0;
}

-		abac	{abac=4 }	ABAC
-		AB	{ab=2 }	AB
-		A	{a=2 }	A
-		__vfptr	0x00415700 const ABAC::`vftable'	*
		[0]	0x0041122b [thunk]:ABAC::do_things`vtordisp{4294967292,0}' (int)	*
		a	2	int
		ab	2	int
-		AC	{ac=4 }	AC
-		A	{a=2 }	A
-		__vfptr	0x00415700 const ABAC::`vftable'	*
		[0]	0x0041122b [thunk]:ABAC::do_things`vtordisp{4294967292,0}' (int)	*
		a	2	int
		ac	4	int
		abac	4	int