Question

为什么我在以下代码段中收到UMR（unInitialized Memory Read）错误。调用派生类的副本构造函数时，我收到UMR错误

class base{
public :

    base(int);
    int id;

    int getid()
    {
        return id;
    }
};

base::base(int a)
{
    id = a;
}

class derived:public base{
public :
    derived(derived &);
    int inum;

    int getnum()
    {
        return inum;
    }

};

derived::derived(derived &d):base(d.getnum()) // UMR Error
{
    inum = id;
}

任何人都可以知道实施有什么问题吗？

Answer 1

派生类永远不会初始化inum变量。错误消息告诉你。 d.getnum()会返回未初始化的inum变量。

Answer 2

我认为你不能编译你的代码，下面是一些问题：

class derived:class base{
               ^^^-> public

应该是：

class derived : public base

更改int getnum(); to int getnum() const;

derived::derived(derived &d):base(d.getnum) // UMR Error
                                         ^^^ function call?

为什么用derived :: inum初始化base :: id？

应该是：

   derived::derived(const derived &d) : base(d) // initialize base with base
   {
                    ^^^  copy constructor has const 
      inum = d.inum;  // initialize derived member
      // inum = id;  why you assign id back to inum again?
   }

为什么我在下面的代码片段中收到UMR（unInitialized Memory Read）错误

2 个答案: