VS2008 C + + Object Memory layout (2): Simple inheritance

This time we add a subclass with no virtual functions for both the parent class and the subclass:

class CParent
{
public:
　int parent_a;
　int parent_b;

public:
　void parent_f1()
　{
　　parent_a = 0x10;
　}
　void parent_f2()
　{
　　parent_b = 0x20;
　}
};

class CChild : public CParent
{
public:
　int child_a;
　int child_b;

public:
　void child_f1()
　{
　　child_a = 0x30;
　}
　void child_f2()
　{
　　child_b = 0x40;
　}
};

1.1.1 Memory Layout

Assign a few values to these member variables first:

child.parent_a = 1;
0041138E C7 05 50 71 41 00 01 00 00 00 mov　　　　　　　　 dword ptr [child (417150h)],1
　　　　 child.parent_b = 2;
00411398 C7 05 54 71 41 00 02 00 00 00 mov　　　　　　　　 dword ptr [child+4 (417154h)],2
　　　　 child.child_a = 3;
004113A2 C7 05 58 71 41 00 03 00 00 00 mov　　　　　　　　 dword ptr [child+8 (417158h)],3
　　　　 child.child_b = 4;
004113AC C7 05 5C 71 41 00 04 00 00 00 mov　　　　　　　　 dword ptr [child+0Ch (41715Ch)],4

Observe the contents of the memory area that &child refers to:

01 00 00 00 02 00 00 00 03 00 00 00 04 00 00 00 .......

Obviously, vs merges the data members of the parent class and subclass into the same memory area, but also does not add anything extra to it, the &child pointer points to the first member Parent_a.

1.1.2 Function call

Observe function calls:

child.parent_f1();
00411840 B9 50 71 41 00　　 mov　　　　　　　　 ecx,offset child (417150h)
00411845 E8 78 F9 FF FF　　 call　　　　　　　 CParent::parent_f1 (4111C2h)
　　　　 child.child_f1();
0041184A B9 50 71 41 00　　 mov　　　　　　　　 ecx,offset child (417150h)
0041184F E8 64 F9 FF FF　　 call　　　　　　　 CChild::child_f1 (4111B8h)

is no different from a function call to a simple parent class. Pass the this pointer with ECX.