找错，一道华为的面试题

vigoqiu

class Base
{
  public:
  Base() {}
  ~Base() {}
};

class A : public Base
{
public:
  A() {m_pData = NULL;}
  A(int nSize) { m_pData = new int[nSize]; }
~A() { delete []m_pData; }
   

private:
  int * m_pData;
};

void main()
{
   Base * b = new A(100);
   delete b;
}

找出错误，说明原因，应该如何“合理”地改正？
大师们发表下意见

夜荷

目前的程序没看到错误，但是如果
void main()
{
   Base * b = new A();
   delete b;
}
就会发生内存释放错误。

saimk2

由于编译期间b的析构函数地址已经被确定导致A的析构函数没有被调用（真绕口－－b），从而发生内存泄漏，改正方法：～Base()前加上个virtual修饰

aear

class Base
{
  public:
  Base() {}
  virtual ~Base() {}  // should be virual base
};

class A : public Base
{
// should put data members ahead of methods if they are used in the
// rest of class declaration
private:
  int * m_pData;  

public:
  // one constructor is pretty enough, and "explicit" keyword sould be
  // used
  explicit A(int nSize = 0) : m_pData(NULL) {
     // exception is not mandatory, but it's better to have it in constructors
     try {
        if( nSize ) m_pData = new int[nSize];
     } catch (...) {...};
  }
~A() { delete []m_pData; }
   
  // because there is a pointer in the class, either you provide copy
  // constructor and operator = , or make them private
private:
   A(const A &);
   A & operator = (const A &);
};


Conclusion
If the correct answer to this quesion is only the "virtual", either you or
the person who wrote this question should Tan JJ Dao Si

千里马肝

bravo!
aear's answer is very clear.

halei

额...马肝大大已经结案了啊....来晚了....

大树懒

基类的析构函数要是virtual，哈哈

neelkey

~A() { delete []m_pData; }

delete前必须做 if(m_pData) 的判断

lingjingqiu

Tan JJ Dao Si

----------------????

千里马肝

delete空指针将会直接返回，所以是安全的，毋须判断
除非是同一个指针会多次使用时才需要注意该情况