【C++】Accessor and Mutator Functions & 函数形参与类私有成员重名的解决方法

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;
    }
};
  • 通过引用this指针,可以明确复制号的左操作数是调用函数的对象里面的width和height,而不是传进去的参数,从而不会引起混淆。

  • 当然了,这种设形参的方法本来就不太好,如果不是题目要求而是自己编程的时候应该尽量避免使用。

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