C / C++ / MFC

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

Jung Seng Won wrote:

USB control system is allowing computer to use USB that is registered by administrator.
if you want to use USB in your computer, you should input your password.

Jung Seng Won wrote:

but i just have idea , and i don't know what should i do first....

My friend don't know ...

so can you please give me tip and
recommand book which i can reference?

Jung Seng Won wrote:

(i can do c, c++ not winapi or MFC)

clever101 wrote:

(Press Retry to debug the application)

Mark Salsbery
Microsoft MVP - Visual C++