记录:C++类内存分布(虚继承与虚函数)

时间:2020-12-27 04:56:27

工具:VS2013

先说一下VS环境下查看类内存分布的方法:

记录:C++类内存分布(虚继承与虚函数)

记录:C++类内存分布(虚继承与虚函数)

先选择左侧的C/C++->命令行,然后在其他选项这里写上/d1 reportAllClassLayout,它可以看到所有相关类的内存布局,如果写上/d1 reportSingleClassLayoutXXX(XXX为类名),则只会打出指定类XXX的内存布局。

编译后,输出如图的内存布局:

记录:C++类内存分布(虚继承与虚函数)

测试代码

#include <iostream>

using namespace std;

typedef void(*FUN)();

class A{
public:
int a; virtual void print(){}
virtual void print_a(){
cout << "print_a()" << endl;
}
}; class B : virtual public A{
public:
int b;
void print(){}
virtual void print_b(){
cout << "print_b()" << endl;
}
}; class C : virtual public A{
public:
int c; void print(){}
virtual void print_c(){
cout << "print_c()" << endl;
}
}; class D : public B, public C{
public:
int d; void print(){}
virtual void print_d(){
cout << "print_d()" << endl;
}
}; int main()
{
D derived; FUN *pFun = (FUN*)((*(int*)(A*)(&derived) + 4)); (*pFun)(); system("Pause"); return 0;
}

对象内存分布

1>  class A	size(8):
1> +---
1> 0 | {vfptr}
1> 4 | a
1> +---
1>
1> A::$vftable@:
1> | &A_meta
1> | 0
1> 0 | &A::print
1> 1 | &A::print_a
1>
1> A::print this adjustor: 0
1> A::print_a this adjustor: 0
1>
1>
1> class ?$is_error_code_enum@PBD size(1):
1> +---
1> | +--- (base class ?$integral_constant@_N$0A@)
1> | +---
1> +---
1>
1>
1>
1> class B size(20):
1> +---
1> 0 | {vfptr}
1> 4 | {vbptr}
1> 8 | b
1> +---
1> +--- (virtual base A)
1> 12 | {vfptr}
1> 16 | a
1> +---
1>
1> B::$vftable@B@:
1> | &B_meta
1> | 0
1> 0 | &B::print_b
1>
1> B::$vbtable@:
1> 0 | -4
1> 1 | 8 (Bd(B+4)A)
1>
1> B::$vftable@A@:
1> | -12
1> 0 | &B::print
1> 1 | &A::print_a
1>
1> B::print this adjustor: 12
1> B::print_b this adjustor: 0
1>
1> vbi: class offset o.vbptr o.vbte fVtorDisp
1> A 12 4 4 0
1>
1>
1> class C size(20):
1> +---
1> 0 | {vfptr}
1> 4 | {vbptr}
1> 8 | c
1> +---
1> +--- (virtual base A)
1> 12 | {vfptr}
1> 16 | a
1> +---
1>
1> C::$vftable@C@:
1> | &C_meta
1> | 0
1> 0 | &C::print_c
1>
1> C::$vbtable@:
1> 0 | -4
1> 1 | 8 (Cd(C+4)A)
1>
1> C::$vftable@A@:
1> | -12
1> 0 | &C::print
1> 1 | &A::print_a
1>
1> C::print this adjustor: 12
1> C::print_c this adjustor: 0
1>
1> vbi: class offset o.vbptr o.vbte fVtorDisp
1> A 12 4 4 0
1>
1>
1> class D size(36):
1> +---
1> | +--- (base class B)
1> 0 | | {vfptr}
1> 4 | | {vbptr}
1> 8 | | b
1> | +---
1> | +--- (base class C)
1> 12 | | {vfptr}
1> 16 | | {vbptr}
1> 20 | | c
1> | +---
1> 24 | d
1> +---
1> +--- (virtual base A)
1> 28 | {vfptr}
1> 32 | a
1> +---
1>
1> D::$vftable@B@:
1> | &D_meta
1> | 0
1> 0 | &B::print_b
1> 1 | &D::print_d
1>
1> D::$vftable@C@:
1> | -12
1> 0 | &C::print_c
1>
1> D::$vbtable@B@:
1> 0 | -4
1> 1 | 24 (Dd(B+4)A)
1>
1> D::$vbtable@C@:
1> 0 | -4
1> 1 | 12 (Dd(C+4)A)
1>
1> D::$vftable@A@:
1> | -28
1> 0 | &D::print
1> 1 | &A::print_a
1>
1> D::print this adjustor: 28
1> D::print_d this adjustor: 0
1>
1> vbi: class offset o.vbptr o.vbte fVtorDisp
1> A 28 4 4 0

运行结果

记录:C++类内存分布(虚继承与虚函数)