C++的問題

[lujiaming]

class A1
{
public:
virtual void Test(){}
};

class A2 : public A1
{
public:
virtual void Test(){}
};

class A3 : public A1
{
public:
virtual void Test(){}
};

class A : public A2, public A3
{
};

{
DWORD dw;
dw = (DWORD)((A *)8); //dw = 0x08
dw = (DWORD)((A3 *)(A *)8); //dw = 0x0c
dw = (DWORD)((A1 *)(A3 *)(A *)8); //dw = 0x0c
dw = (DWORD)((A1 *)(A3 *)(A *)8) - 8;//dw = 4
}
這段代碼中(A1 *)(A3 *)(A *)8 是甚麼意思阿

[yheysj]

上面这为仁兄太厉害了！明白了吗？？

[bighead]

type cast?

[karma]

Let me try. This is related to how the virtual table is laid out in the memory
A2 ===> A1 (same location)
A3 ===> A1 (same location)
A ===> A2 ===> A1 ==> if at 8 (4 bytes for the virtual table pointer)
A3 ===> A1 ==> the at 12

A has a size of 8

>>dw = (DWORD)((A *)8); //dw = 0x08
cast 8 to (A*), even in the byte alignment situation, this works

>>dw = (DWORD)((A3 *)(A *)8); //dw = 0x0c
cast (A*)8 to A3*, it becomes 12, as shown above

>>dw = (DWORD)((A1 *)(A3 *)(A *)8); //dw = 0x0c
(A3*)(A*)8 is 12, cast to the A1* part inside A3, same location, so it is 12

>>dw = (DWORD)((A1 *)(A3 *)(A *)8) - 8;//dw = 4
(A1 *)(A3 *)(A *)8 is 12, so dw = 4

[lujiaming]

謝謝無為
能不能給出內存map阿
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