Accessor and Mutator functions

Definition

Accessor and mutator functions (a.k.a. set and get functions) provide a direct way to change or just access private variables.
They must be written with the utmost care because they have to provide the protection of the data that gives meaning to a class in the first place. Remember the central theme of a class: data members are hidden in the private section, and can only be changed by the public member functions which dictate allowable changes.
某个变量只能通过公共方法来存取，这种变量叫做accessor或mutator。
accessor和mutator主要用来实现数据的封装，有了accessor和mutator，我们就可以将数据成员设为私有，所有对它们的读写操作都通过这两个函数来实现。

#include<iostream>
#include<string>

class student{ 
   
private:
     int id；//id这个名称称为accessor存取器或mutator变值器。
public:
     int getId();//accessor function，是只读性质的函数
     void setId(int id);//mutator function，是只写性质的函数
}；

函数形参与类私有成员重名的解决方法

#include<iostream>

class retangle{
private:
    double width;
    double height;
public:
    void setWidth(double width);
    void setHeight(double height);
};

-按照一般做法，我们会这样来实现这两个set函数：

#include<iostream>

class retangle{
private:
    double width;
    double height;
public:
    void setWidth(double width) {
        width = width；//error
        return；
    }
    void setHeight(double height) {
        height = height；//error
        return；
    }
};

但是我们会发现这样是行不通的，会出现编译错误，原因大概是，编译器把两个width和height都当成是传进函数的参数。
这个时候，我们就需要引入this指针来解决这个问题。

#include<iostream>

class retangle{
private:
    double width;
    double height;
public:
    void setWidth(double width) {
        this->width = width；
        return；
    }
    void setHeight(double height) {
        this->height = height；
        return；
    }
};