复制作业应该做什么

Question

我正在寻找以下解释的答案（来自书"A tour of C++"）

MyClass& operator=(const MyClass&) // copy asignment: clean up target and copy

我从来没有清理过目标 （或者至少我不明白它是做什么的mean) 复制时 so:

复制的概念不就是有两个相同的东西吗？
如果我清理目标，那不是move吗？
清理目标到底是什么意思？
- 引用也是const所以我不会可以修改

书中下面写道：

MyClass& operator=(MyClass&&) // move assignment: clean up target and move

这里清理目标是有意义的，因为这是我理解 move -ing 工作的方式

Answer 1

假设 MyClass 有一个拥有指针

class MyClass {
  Owned *that;
public:
...
  MyClass& operator=(const MyClass&other) // copy asignment: clean up target and copy
  {
     Owned = other->owned;
  }

指向的内存发生了什么？它被泄露了。所以改为

  MyClass& operator=(const MyClass&other) // copy asignment: clean up target and copy
  {
     if (this == &other)  // prevent self assignment as this would in this case be a waste of time.
       return *this;
     delete that; // clean up
     that = new Owned(*other->that); // copy
     return *this; // return the object, so operations can be chained.
  }

感谢@PaulMcKenzie && @Eljay

  MyClass& operator=(const MyClass&other) // copy asignment: clean up target and copy
  {
     Owned *delayDelete = that;
     that = new Owned(*other->that); // copy, if this throws nothing happened
     delete delayDelete; // clean up
     return *this; // return the object, so operations can be chained.
  }

复制作业应该做什么

What should a copy assignment do

c++

copy

move