有关删除运算符的问题 [英] Question on delete operator

问题描述

大家好，
我对delete []运算符有以下疑问.
想象一下我有两个班.

Hi people,
I have following question on delete [] operator.
Imagine I have two classes.

Class A
{
....

char * data;

~A() // destructor
{
if (data) delete [] data;
}

}

 

class B
{
A * objectA;

...

~B() // destructor
{
delete objectA;
}

void function()
{
// now imagine here I create a pointer to A object
objectA = new A;
objectA->data = new char [100];
}
}

我的问题是.想象

My question is. Imagine

funtion()

被调用了.然后我调用了B类析构函数-删除对象A的析构函数，这是否意味着指针-> data变量也将被删除? (即，以后我不需要单独

was called. And afterwards class B destructor was called - the one that deletes object A -- my question is, will this imply that pointer->data variable will also be deleted? (i.e., won''t I need to separately

delete [] data 

了吗?-一旦

delete [] data

)

Thanks

is being called in this code)

thanks

推荐答案

在A的构造函数中将data 指针设置为0，就可以了.与您的B类和objectA相同.

在您的function中，没有正在构造的B型对象.但假设您添加了一行

Set your data pointer to 0 in the constructor of A and you will be fine. Same for your class B and objectA.

In your function, there is no object of type B being constructed. But let''s assume you added a line

B b;
b.objectA = new A;

然后，B的构造函数将删除A对象，该对象随后将调用A的析构函数.

顺便说一句，您似乎从未编译过代码. C ++中的关键字类用小写的c拼写.而且您需要在开头加上public:行，否则您的成员变量将无法从外部代码访问.

Then the constructor of B would delete the A object, which in turn would call A''s destructor.

By the way, you seem not have compiled your code ever. The keyword class in C++ is spelled with a lower-case c. And you would need to a public: line at the beginning, or your member variables will not be accessible from outside code.

您的代码无法编译.下面的代码确实并重现了运行时错误:

You code doesn''t compile. The following one does and reproduces the runtime error:

class A
{
    //....
public:
    char * data;

    ~A() // destructor
    {
        if (data) delete [] data;
    }

};

class B
{
    A* objectA;

public:

    ~B() // destructor
    {
        delete objectA;
    }
public:
    void function()
    {
        // now imagine here I create a pointer to A object
        A * pointer = new A;
        pointer->data = new char [100];
    }
};
int main()
{
    B b;
    b.function();
}

您收到错误消息是因为:

You get an error because:

1. 您永远不会为objectA分配内存，而是在B的ctor中删除它.
2. 您永远不会初始化objectA的成员data

1. You never allocate memory for objectA but you delete it inside B''s ctor.
2. You never initialize the objectA''s member data

(注意:与pointer临时变量有关的内存).
解决方法是

(note: memory associated to pointer temporary variable leaks).
A fix would be

class A
{
public:
  //..
  A():data(NULL){}
  //..
};

class B()
{
public:
//..
B():objectA(NULL){}
};

(如果您有更新的编译器，则可以使用nullptr而不是NULL)

总体而言，您的设计看起来并不十分坚固.

(you may use nullptr instead of NULL if you have an updated compiler)

On the overall your design doesn''t look terribly robust.

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