在指针别名中验证悬空指针 [英] Verifying a dangling pointer in pointer aliasing

问题描述

大家好，

我对在指针别名中验证悬空指针有疑问

Hi all,

I have a doubt about verifying a dangling pointer in pointer aliasing

CMyClass* pObj = new CMyClass();

pObj将在其中存储变量的地址(例如K).即pObj指向存储在地址K的变量.
虽然pObj本身将有一些地址(例如X).

pObj will store address (say K) of a variable in it. i.e. pObj pointing to variable stored at address K.
While pObj itself will have some address (say X).

CMyClass* pMirrorObj = pObj;     //Aliased Pointer

pMirrorObj还将在其中存储相同变量的地址.即pMirrorObj也指向存储在地址K的变量.
如果我没记错的话，pMirrorObj的地址可能会有所不同(例如Y).

如上所述，
X-> K
Y-> K

我在不同的代码位置使用了两个指针(pObj和pMirrorObj).

pMirrorObj will also store address of same variable in it. i.e. pMirrorObj also pointing to variable stored at address K.
If I am not wrong, pMirrorObj may have some different address (say Y).

As per the above,
X -> K
Y -> K

I am using both pointers (pObj and pMirrorObj) in different code location.

if( pObj )
{
delete(pObj);
pObj = NULL;
}

以上操作结果，
X-> NULL
Y-> K

如何处理第二个指针(悬空指针)?
我应该使用双指针(CMyClass ** ppMirrorObj =& pObj)而不是单指针(pMirrorObj)来避免删除悬空指针的情况，如下所示，

Result of above operation will,
X -> NULL
Y -> K

How to deal with second pointer (dangling pointer)?
Shall I use as double pointer (CMyClass** ppMirrorObj = &pObj) instead of single pointer (pMirrorObj) to avoid deletion dangling pointer as follows,

if( pMirrorObj )     //assigning NULL to pObj, will not make pMirrorObj as NULL
{
delete(pMirrorObj);
pMirrorObj = NULL;
}

谢谢&问候，
Aniket A. Salunkhe

Thanks & Regards,
Aniket A. Salunkhe

推荐答案

好吧，您可以创建指向新对象的指针

CMyClass * pObj =新的CMyClass();


然后，您可以创建2个指向pObj的指针，而不必复制存储在pObj中的值.

CMyClass ** ptrToOrigPtrA =&pObj;
CMyClass ** ptrToOrigPtrB =&pObj;


如果然后删除(pObj)并将pObj = NULL设置，则* ptrToOrigPtrA和* ptrToOrigPtrB都将为NULL.
因此，由于您可以看到它们指向一个持有NULL的内存位置，因此您知道尝试通过** ptrToOrigPtrA或** ptrToOrigPtrB引用原始对象将是一个坏消息.


所以，是的-您应该使用双指针". :)

Well, you could create a pointer to the new object

CMyClass *pObj = new CMyClass();


Then instead of copying the value stored in pObj, you can create 2 pointers to pObj.

CMyClass **ptrToOrigPtrA = &pObj;
CMyClass **ptrToOrigPtrB = &pObj;


If you then delete(pObj) and set pObj = NULL, then both *ptrToOrigPtrA & *ptrToOrigPtrB will also be NULL.
So, since you can see that they point to a memory location holding NULL you then know that trying to reference the original object via **ptrToOrigPtrA or **ptrToOrigPtrB will be bad news.


So, yes - you should use ''double-pointers''. :)

您可以看看智能指针(例如，参见 ^ ] ).

You may have a look at smart pointers (see, for instance Wikipedia[^]).

您差一点就拥有了.

You nearly had it.

CMyClass* pObj = new CMyClass();  // Pointer to object
CMyClass** ppMirrorObj = &pObj;   // Pointer to pointer to object

现在您可以:

Now you can:

delete (*ppMirrorObj); // Deletes object pObj points to
*ppMirrorObj = NULL;  // pObj now NULL

或

OR

delete (pObj);  // Deletes object pObj points to

pObj = NULL;  // pObj now NULL

删除NULL指针无效，因此无需检查NULL.

Deleting a NULL pointer has no effect so no need to check for NULL.

这篇关于在指针别名中验证悬空指针的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！