C++默认构造函数,用新对象初始化指针

Question

我有以下问题:在myClass中我想默认初始化一个指向yourClass的指针,带有一个新的yourClass地址.不幸的是,如果我想在任何一点删除指针,我得到一个(核心转储).

class myClass
{
      protected:
      yourClass * yc;

      public:
      myClass() { yc = new yourClass(); }

      myClass(yourClass * tyc ) { delete yc; yc = tyc; }

      ~myClass() { delete yc; yc = NULL; }

      void setMyClass (yourClass * tyc) { delete yc; yc = tyc; }

      void print () { yc->print(); }
};

int main()
{
  yourClass b (//parameter);
  myClass * a = new myClass();
  a->print();
  a->setMyClass(&b)
  a->print();

  delete a;
  return 0;
}

a的print()应该产生两种不同的打印,取决于//参数.

我认为你的等级是yc; 而不是yourClass*yc,但我想知道它是否可行.

编辑: 我以下面的方式重新编写代码,它的工作原理.仍然看起来很复杂,聪明的指针看起来很有希望,我仍然没有应用"三个规则".这里的代码.谢谢大家.

class myClass
{
      protected:
      yourClass * yc;
      bool dynamic;

      public:
        myClass() { dynamic = true; yc = new yourClass (); }
        myClass (yourClass * tyc ) 
        { 
          // dynamic init (like default)
          if (tyc == NULL ) { dynamic = true; yc = new yourClass (); }
          // static use of yc
          else { dynamic = false; yc = tyc; } 
        }
        // because only if dynamic is true, we need to erase
        ~blu () { if (dynamic) { delete yc; dynamic = false; } } 

        void setMyClass(yourClass* tyc) 
        { 
          // leaving unchanged if new-stuff is NULL or like old-stuff
          if ( tyc == yc || tyc == NULL ) return;
          else // treating dynamic and static differently
          { 
            if (dynamic) // if flag is set, must be deleted 
            {
              delete yc; yc = tyc; dynamic = false;
            }
            else // must not be deleted, dynamic is still false
            {
              yc = tyc;
            }
          }
        }
        void print () { yc->print(); }
};

Answer 1

那是因为你试图删除太多:

• 您正在删除第二个构造函数中的未分配对象(删除delete yc;)
• 您正在尝试删除堆栈分配的对象,b.delete a;将尝试删除指向b的指针,b是堆栈中的对象; 会发生什么取决于您的操作系统(我期待异常/核心转储/无论如何)

编辑:我发现的另一个问题.. a->setMyClass(NULL)

我会建议:

• 关于智能指针的这篇文章
• 这篇关于RAII的博客文章
• 任何解释堆栈与堆分配的C/C++入门(静态与动态？)