C++实用教程（四）：面向对象核心多态笔记

推荐B站视频：C++现代实用教程(四):面向对象核心多态_哔哩哔哩_bilibilihttps://www.bilibili.com/video/BV15v4y1M7fF/?spm_id_from=333.999.0.0&vd_source=a934d7fc6f47698a29dac90a922ba5a3

本项目通用的tasks.json文件和launch.json

tasks.json

{
    "version": "2.0.0",
    "options": {
        "cwd": "${workspaceFolder}/build"
    },
    "tasks": [
        {
            "type": "shell",
            "label": "cmake",
            "command": "cmake",
            "args": [
                ".."
            ]
        },
        {
            "label": "make",
            "group": "build",
            "command": "make",
            "args": [],
            "problemMatcher": []
        },
        {
            "label": "Build",
            "dependsOrder": "sequence",
            "dependsOn": [
                "cmake",
                "make"
            ]
        },
        {
            "type": "cppbuild",
            "label": "C/C++: g++ 生成活动文件",
            // "command": "/usr/bin/g++",
            "command": "D://mingw64//bin//g++.exe",
            "args": [
                "-fdiagnostics-color=always",
                "-g",
                "-o",
                "${workspaceFolder}/bin/app.exe",
                // "-finput-charset=UTF-8",
                /*
                    -fexec-charset指定输入文件的编码格式
                    -finput-charset指定生成可执行的编码格式,
                */
                "-finput-charset=GBK",  // 处理mingw中文编码问题
                "-fexec-charset=GBK"
            ],
            "options": {
                "cwd": "${workspaceFolder}"
            },
            "problemMatcher": [
                "$gcc"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            },
            "detail": "D://mingw64//bin//g++.exe"
        }
    ]
}

launch.json

{
    // 使用 IntelliSense 了解相关属性。 
    // 悬停以查看现有属性的描述。
    // 欲了解更多信息，请访问: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "(gdb) 启动",
            "type": "cppdbg",
            "request": "launch",
            "program": "${workspaceFolder}/bin/app.exe",
            "args": [],
            "stopAtEntry": false,
            "cwd": "${workspaceFolder}",
            "environment": [],
            "externalConsole": false,
            "MIMode": "gdb",
            "setupCommands": [
                {
                    "description": "为 gdb 启用整齐打印",
                    "text": "-enable-pretty-printing",
                    "ignoreFailures": true,
                },
            ],
            "preLaunchTask": "Build",
            "miDebuggerPath": "D://mingw64//bin//gdb.exe", // 修改为你的 gdb 路径
        },
    ]
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.28.0)
project(project)
include_directories(${PROJECT_SOURCE_DIR}/include)
aux_source_directory(${PROJECT_SOURCE_DIR}/src SRC_LIST)

add_executable(app main.cpp ${SRC_LIST})
set(EXECUTABLE_OUTPUT_PATH ${PROJECT_SOURCE_DIR}/bin)

C++的面向对象与很多其他的面向对象语言有很多不同，本质的原因是在于C++是一门极其重视性能的编程语言

>>多态是面向对象的核心

这一点对于C++来说也不例外
面向对象的三大特性为：封装、继承、多态
- 本人不是很喜欢C++的继承，其实是不喜欢继承
- 封装和继承基本上是为多态而准备的
面向对象是使用多态性获得对系统中每个源代码依赖项的绝对控制的能力的（大牛说的）
高内聚、低耦合是程序设计的目标（无论是否面向对象，），而多态是实现高内聚，低耦合的基础

>>目录

    1.多态与静态绑定

    2.虚函数与动态绑定

    3.多态对象的应用场景与大小

    4.Override与Final

    5.Overloading与多态

    6.析构函数与多态

    7.Dynamic_cast类型转换

    8.typeid操作符

    9.纯虚函数与抽象类

    10.接口式抽象类

第一节：多态与静态绑定

>>多态：

在编程语言和类型论中，多态（英语：polymorphism）指为不同数据类型的实体提供统一的接口
多态意味着调用成员函数时，会根据调用函数的对象的类型来执行不同的函数

>>静态绑定：将名称绑定到一个固定的函数定义，然后在每次调用该名称时执行该定义，这个也是常态执行的方式

shape.h

#ifndef SHAPE_H
#define SHAPE_H
#include <string>
#include <string_view>
#include <iostream>
class Shape{
public:
    Shape() = default;
    ~Shape() = default;
    Shape(std::string_view name);
    void draw() const {
        std::cout<<"Shape Drawing "<<m_name<<std::endl;
    }
protected:
    std::string m_name;
};
#endif

shape.cpp

#include "shape.h"

Shape::Shape(std::string_view name) : m_name(name){

}

rectangle.h

#ifndef RECTANGLE_H
#define RECTANGLE_H
#include <string>
#include <string_view>
#include <iostream>
#include "shape.h"
class Rectangle:public Shape{
public:
    Rectangle() = default;
    ~Rectangle() = default;
    Rectangle(double x,double y,std::string_view name);

    void draw() const {
        std::cout<<"Rectangle Drawing "<<m_name<<" with x: "<<get_x()<<",y: "<<get_y()<<std::endl;
    }
protected:
    double get_x() const{
        return m_x;
    }
    double get_y() const{
        return m_y;
    }
private:
    double m_x{0.0};
    double m_y{0.0};
};
#endif

rectangle.cpp

#include "rectangle.h"

Rectangle::Rectangle(double x, double y,std::string_view name)
    : Shape(name),m_x(x),m_y(y)
{

}

square.h

#ifndef SQUARE_H
#define SQUARE_H
#include "rectangle.h"
class Square:public Rectangle{
public:
    Square() = default;
    ~Square() = default;
    Square(double x,std::string_view name);

    void draw() const {
        std::cout<<"Square Drawing "<<m_name<<" with x: "<<get_x()<<std::endl;
    }
};
#endif

square.cpp

#include "square.h"

Square::Square(double x, std::string_view name)
    : Rectangle(x,x,name)
{
}

main.cpp

#include <iostream>
#include "square.h"
#include "rectangle.h"
#include "shape.h"
using namespace std;

// Shape -> Rectangle -> Square
// draw()
void test1() {
    // 静态绑定的不足
    Shape s1("Shape1");
    s1.draw();// Shape Drawing Shape1

    Rectangle r1(1.0,2.0,"Rectangle1");
    r1.draw();// Rectangle Drawing Rectangle1 with x: 1,y: 2

    Square sq1(3.0,"Square1");
    sq1.draw();// Square Drawing Square1 with x: 3

    // Base Pointer
    Shape* shape_ptr = &s1;
    shape_ptr->draw();// Shape Drawing Shape1
    shape_ptr = &r1;
    shape_ptr->draw();// Shape Drawing Rectangle1
    shape_ptr = &sq1;
    shape_ptr->draw();// Shape Drawing Square1
}

int main(int argc,char* argv[]) {
    test1();
    cout<<"over~"<<endl;
    return 0;
}

执行结果：

PS D:\Work\C++UserLesson\cppenv\static_bind\build> ."D:/Work/C++UserLesson/cppenv/static_bind/bin/app.exe"
Shape Drawing Shape1
Rectangle Drawing Rectangle1 with x: 1,y: 2
Square Drawing Square1 with x: 3
Shape Drawing Shape1
Shape Drawing Rectangle1
Shape Drawing Square1
over~
PS D:\Work\C++UserLesson\cppenv\static_bind\build>

第二节：虚函数与动态绑定

>>动态绑定

实现继承
父类、子类需要动态绑定的函数设置为虚函数
创建父类指针/引用（推荐指针）指向子类对象，然后调用

>>虚函数

虚函数是应在派生类中重新定义的成员函数
关键字为virtual

通过例子来实现多态

shape.h

#ifndef SHAPE_H
#define SHAPE_H
#include <string>
#include <string_view>
#include <iostream>
class Shape{
public:
    Shape() = default;
    ~Shape() = default;
    Shape(std::string_view name);
    virtual void draw() const {
        std::cout<<"Shape Drawing "<<m_name<<std::endl;
    }
protected:
    std::string m_name;
};
#endif

shape.cpp

#include "shape.h"

Shape::Shape(std::string_view name) : m_name(name){

}

rectangle.h

#ifndef RECTANGLE_H
#define RECTANGLE_H
#include <string>
#include <string_view>
#include <iostream>
#include "shape.h"
class Rectangle:public Shape{
public:
    Rectangle() = default;
    ~Rectangle() = default;
    Rectangle(double x,double y,std::string_view name);

    virtual void draw() const {
        std::cout<<"Rectangle Drawing "<<m_name<<","<<"x: "<<get_x()<<",y: "<<get_y()<<std::endl;
    }
protected:
    double get_x() const{
        return m_x;
    }
    double get_y() const{
        return m_y;
    }
private:
    double m_x{0.0};
    double m_y{0.0};
};
#endif

rectangle.cpp

#include "rectangle.h"

Rectangle::Rectangle(double x, double y,std::string_view name)
    : Shape(name),m_x(x),m_y(y)
{

}

square.h

#ifndef SQUARE_H
#define SQUARE_H
#include "rectangle.h"
class Square:public Rectangle{
public:
    Square() = default;
    ~Square() = default;
    Square(double x,std::string_view name);

    void draw() const {
        std::cout<<"Square Drawing "<<m_name<<" with x: "<<get_x()<<std::endl;
    }
};
#endif

square.cpp

#include "square.h"

Square::Square(double x, std::string_view name)
    : Rectangle(x,x,name)
{
}

执行结果：

PS D:\Work\C++UserLesson\cppenv\dynamic_bind\bin> ."D:/Work/C++UserLesson/cppenv/dynamic_bind/bin/app.exe"
Shape Drawing Shape1
Rectangle Drawing Rectangle1,x: 1,y: 2
Square Drawing Square1 with x: 3
over~
PS D:\Work\C++UserLesson\cppenv\dynamic_bind\bin>

未完待续~

本文来自互联网用户投稿，该文观点仅代表作者本人，不代表本站立场。本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如若转载，请注明出处：/a/349416.html

如若内容造成侵权/违法违规/事实不符，请联系我们进行投诉反馈qq邮箱809451989@qq.com，一经查实，立即删除！