為什么我在以下代碼段中收到UMR（未初始化的內存讀取）錯誤

Question

為什么在以下代碼段中出現UMR（未初始化內存讀取）錯誤。 調用派生類的副本構造函數時出現UMR錯誤

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;
}

有人能知道實現有什么問題嗎？

Answer 1

您派生的類永遠不會初始化inum變量。 錯誤消息告訴您。 d.getnum()返回未初始化的inum變量。

Answer 2

我認為您無法編譯代碼，以下是一些問題：

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

應該：

class derived : public base

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

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

為什么用派生:: inum初始化base :: id？

應該：

   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?
   }