4级继承链中的C ++虚拟析构函数. [英] C++ Virtual Destructors in a 4 level inheritance chain.
问题描述
我正在对虚拟析构函数进行一些小实验以进行审查-想知道是否有人对以下内容有简单的解释(使用vs 2010):
I was doing a little experiment with virtual destructors to review - wondering if anyone has a simple explanation for the following (using vs 2010):
我定义类层次结构A-B-C-D，D继承C，C继承B，B继承A，A是基数;
I Define class hierarchy A-B-C-D, D inherits C, C inherits B, B inherits A, A is the Base;
进行了2个实验:
第一个实验-
A有一个虚拟的析构函数.
A has a virtual Destructor.
B具有非虚拟析构函数
B has a non-Virtual Destructor
C有一个虚拟的析构函数
C has a virtual Destructor
D具有非虚拟的析构函数
D has a non virtual Destructor
//----------------------------
//----------------------------
在类型D的堆上分配4个对象-将A *，B *和C *的指针指向前3个-将第4个对象作为D *保留完整性. 删除所有4个指针.
Allocate 4 objects on the heap of type D - Point a pointer of A*, B* and C* at the first 3 - Leave the 4th as a D* for Completeness. Delete all 4 Pointers.
如我所料，在所有4种情况下，完整的析构函数链都以相反的顺序从D向下执行到A，从而释放了所有内存.
As I expected, in all 4 instances, the complete destructor chain is executed in reverse order from D down to A, freeing all memory.
第二个实验-
A具有非虚拟的析构函数，**将A更改为非虚拟的
A has a non-virtual Destructor ** Changed A to non virtual
B具有非虚拟析构函数
B has a non-Virtual Destructor
C有一个虚拟的析构函数
C has a virtual Destructor
D具有非虚拟Distructor
D has a non virtual Distructor
在类型D的堆上分配4个对象-将A *，B *和C *的指针指向前3个-将第4个对象作为D *保留完整性.
Allocate 4 objects on the heap of type D - Point a pointer of A*, B*, and C* at the first 3 - Leave the 4th as a D* for Completeness.
删除C *和D *指针: 完整的析构函数链以从D到A的相反顺序执行，从而释放了所有内存.
Deleting C* and D* pointers: the complete destructor chain is executed in reverse order from D down to A, freeing all memory.
删除B *: B然后运行A析构函数(泄漏)
Deleting B*: B and then A Destructor is run (leak)
删除A *: 仅运行析构函数(泄漏)
Deleting A*: Only A Destructor is run (leak)
任何人都可以解释这是为什么吗?
Can anyone explain Why this is?
在实验2中分配了D类对象时，其直接基类(C)具有虚拟析构函数-这不是告诉编译器使用Vptr对其进行跟踪并知道内存类型吗?不管参考资料吗?
When D type opjects are allocated in experiment 2, its immediate base class (C) has a virtual destructor - doesnt that tell the compiler to track it with a Vptr and know the memory type? REGARDLESS of the reference?
谢谢 迈克
推荐答案
在实验2中分配了D类对象时，其直接基类(C)具有虚拟析构函数-这不是告诉编译器使用Vptr对其进行跟踪并知道内存类型吗?不管参考资料吗?
When D type opjects are allocated in experiment 2, its immediate base class (C) has a virtual destructor - doesnt that tell the compiler to track it with a Vptr and know the memory type? REGARDLESS of the reference?
否.
在第二个测试用例中，A和B没有vptrs/vtables. (即使它们确实做到了，非虚拟成员函数仍将静态地解决，而不是动态地解决.)
In your second test case, A and B don't have vptrs/vtables. (And even if they did, a non-virtual member function would still be resolved statically, not dynamically.)
换一种说法，基类不继承"派生类的信息(例如，函数是否是虚拟的).
Put another way, a base class does not "inherit" information (such as whether functions are virtual) from derived classes.
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