通过类函数返回一个引用并在c ++中返回一个整个对象？ [英] Return a reference by a class function and return a whole object in c++?

问题描述

运算符在类CVector中重载：

Operator overloading in class CVector:

CVector CVector::operator+ (CVector param) {
  CVector temp;
  temp.x = x + param.x;
  temp.y = y + param.y;
  return (temp);
}

和主要：

CVector a (3,1);
  CVector b (1,2);
  CVector c;
  c = a + b;

因此，一个对象通过值传递，然后另一个临时对象正在创建。我猜b是通过值，a是调用+，因此x和y属于a和pram.x和param.y到b。返回temp并且复制赋值运算符将temp的值传递给c？

So an object is passed by value, and then another temp object is being created. I guess b is being passed by value, a is the one calling the + therefore the x and y belong to a and pram.x and param.y to b. temp is returned and the the copy assignment operator delivers temp's values to c?

但是这是什么：

CVector& CVector::operator= (const CVector& param)
{
  x=param.x;
  y=param.y;
  return *this;
}

和主要：

a=b;

再次a调用=和b通过引用传递给const。它是重要的，如果它是通过值？）这是我困惑，x属于a是分配param.x的be。所以为什么不是这个函数void，因为x和y可以通过这个函数访问。什么返回*这意味着，我知道这是调用函数的对象的地址，所以*这将是函数本身，但如果我们返回一个对象，我们需要将它分配到某个地方像前面的c = temp after temp = a + b？
什么是CVector&甚至意味着，它看起来不像我们期望一个CVector类型的对象的地址？

Again a is calling the = and b is being passed by reference as const.(in this case does it matter if it was passed by value?) This is where i get confused, x belonging to a is assigned param.x of be. so why isn't this function void, since x and y can be accessed by this function. What does return *this means, i know that this is the address of the object calling the function, so *this would be the function itself, but if we are returning an object we need to assign it it somewhere like the previous c=temp after temp=a+b? And what does CVector& even mean, it doesn't look like we are expecting an address of an object of CVector type?

换句话说，为什么不是该函数只是：

In other words why isn't the function just:

void CVector::operator= (const CVector& param)
    {
      x=param.x;
      y=param.y;
    }

然后有这个代码

#include <iostream> 
using namespace std;
 class Calc { 
private: 
  int value; 
public: 
  Calc(int value = 0) { this->value = value; } 
  Calc& Add(int x) { value += x; return *this; } 
  Calc& Sub(int x) { value -= x; return *this; } 
  Calc& Mult(int x) { value *= x; return *this; } 
  int GetValue() { return value; } }; 

int main() { 
  Calc cCalc(2); 
  cCalc.Add(5).Sub(3).Mult(4); 
  cout << cCalc.GetValue(); 
  return 0; 
}

现在如果我删除&从函数：

Now if i removed the & from the functions:

  Calc Add(int x) { value += x; return *this; } 
  Calc Sub(int x) { value -= x; return *this; } 
  Calc Mult(int x) { value *= x; return *this; } 

并使用

Calc cCalc(2)
cCalc.Add(5);
cCalc.Sub(3);
cCalc.Mult(4);

而不是前者，它会产生相同的resault。
那么为什么Calc&返回类型允许链接。

instead of the former, it would produce the same resault. So why does Calc& returne type allow chaining.

我不仅想知道如何编程，因为面向对象是很多写一个模式（这是这样写的，这是需要的if反对结构化编程，你必须使用逻辑，但也知道为什么是代码定义的和平，为什么它不是我直觉上认为它应该是（虽然我只学习编程的一个年）。

I not only want to know how to program, since object oriented is much writing by a pattern (this is written like this, this is needed if that) opposed to structured programming where you have to use logic, but also to know why is a peace of code defined as it is, and why it isn't as i intuitively think it should be(although i only learn programming for about a year).

谢谢！

推荐答案

所以为什么不是这个函数void，因为x和y可以被这个函数访问。什么是return *这意味着

so why isn't this function void, since x and y can be accessed by this function. What does return *this means

由于 operator =（）返回一个引用， return * this; 返回对当前对象的引用。这允许我们链式分配运算符。例如，

Since operator=() is declared to return a reference, return *this; returns a reference to the current object. This allows us to chain assignment operators. For example,

a = b = c;

会调用 b.operator =（c）; 并返回对 b 的引用。然后通过等价于 a.operator =（b）的调用分配

will call b.operator=(c); and return a reference to b. Then a is assigned by a call which is equivalent to a.operator=(b).

这篇关于通过类函数返回一个引用并在c ++中返回一个整个对象？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！