c++ - 检测到堆损坏 - 带指针的类

Question

以下代码会导致断言错误。此外，警告错误消息指示检测到堆损坏。

class A {
    int* a; // dynamic array of ints
    A() {};
    A(int size) {
        a = new int[size]; 
    }
    ~A() {
        delete [] a;
        a = nullptr;
    }
}

*** in code somewhere ***
int size = 5;
A temp = A(size);

Answer 1

错误原因是:
A temp = A(size);
此行调用:

1. A 的复制构造函数，这里:A temp = A(size)； 问题是，这会创建一个浅拷贝，因为它使用默认的拷贝构造函数，而我们在类中有一个指针，需要深拷贝!
2. A 的参数化构造函数，此处:A(size)；
3. A 的析构函数，它将删除我们由 A temp 创建的指针并将其置空。

然后当 temp 变量超出范围时，它的 Destructor 将被再次 调用，从而导致断言失败。

Solutions:

1. A temp(size);
instead of A temp = A(size);
this will only call the parametrized constructor.
or
2. Overwrite the default copy constructor to create a deep copy!

Another correction by Marco Costa
It is better to initialize a to nullptr in the default constructor.

Another correction by user4581301
Destructor should check, if a is a nullptr, before deleting.

Additional readings:
1. Why aren't pointers initialized with NULL by default?
2. Rule-of-Three becomes Rule-of-Five with C++11? suggested by Chad
3. scalar deleting destructor issue suggested by Chad