【C++】【学习笔记】【019】覆盖方法和重载方法

覆盖方法：

1、当我们需要在基类里提供一个通用的函数，但在它的某个子类里需要修改这个方法的实现，在C++里，覆盖（overriding）就可以做到。简言之，覆盖方法就是共性里面寻找特性；

2、覆盖的实现：在子类里重新声明这个方法，然后再改写一下它的实现代码就行了，就像是一个新增加的方法一样；

3、子类里的方法，如果和基类里的方法名字一样，不管参数是否一样，都会把基类里的所有同样名字的方法覆盖的；

样例：为Animal添加eat()方法，并在Pig和Turtle中进行覆盖；

#include <iostream>#include <string>// 动物基类class Animal{public:    std::string mouth;    void eat();    void sleep();    void drool(); // 流口水};void Animal::eat(){    std::cout << "Animal: I'm eating!" << std::endl;}void Animal::sleep(){    std::cout << "Animal: I'm sleeping!" << std::endl;}void Animal::drool(){    std::cout << "Animal: I'm drooling!" << std::endl;}// 猪子类class Pig : public Animal{public:    void climb();    void eat();};void Pig::climb(){    std::cout << "Pig: I'm climbing!" << std::endl;}// 覆盖基类的eat方法void Pig::eat(){    Animal::eat();    std::cout << "Pig: I'm eating!" << std::endl;}// 乌龟子类class Turtle : public Animal{public:    void swim();    void eat();};void Turtle::swim(){    std::cout << "Turtle: I'm swimming!" << std::endl;}void Turtle::eat(){    Animal::eat();    std::cout << "Turtle: I'm eating!" << std::endl;}int main(){    Pig pig;    Turtle turtle;    pig.eat();    turtle.eat();    pig.climb();    turtle.swim();    return 0;}

输出：Animal: I'm eating!Pig: I'm eating!Animal: I'm eating!Turtle: I'm eating!Pig: I'm climbing!Turtle: I'm swimming!

重载方法：

1、重载机制：使得可以定义多个同名的方法（函数），只是他们的输入参数必须不同。编译器是依靠不同的输入参数来区分不同的方法；

2、重载并不是一个真正的面向对象特性，它只是可以简化编程工作的捷径，而简化编程工作正是C++的全部追求；

注意：

1、对方法（函数）进行重载一定要有的放矢，重载的方法（函数）越多，程序就越不容易看懂；

2、对方法进行覆盖（注意区分覆盖和重载）时一定要看仔细，因为只要声明的函数输入参数和返回值与原来的不一致，则该方法将是一个重载方法而不是覆盖方法。这种错误很难调试；

3、对从基类继承来的方法进行重载，程序永远不会像预期的那样工作（继承之后尝试的重载本质上是覆盖）；

样例：为Animal添加eat(int eatCount)方法，进行重载；

#include <iostream>#include <string>// 动物基类class Animal{public:    std::string mouth;    void eat();    void eat(int eatCount);    void sleep();    void drool(); // 流口水};void Animal::eat(){    std::cout << "Animal: I'm eating!" << std::endl;}void Animal::eat(int eatCount){    std::cout << "Animal: I'm eating " << eatCount << " foods." << std::endl;}void Animal::sleep(){    std::cout << "Animal: I'm sleeping!" << std::endl;}void Animal::drool(){    std::cout << "Animal: I'm drooling!" << std::endl;}// 猪子类class Pig : public Animal{public:    void climb();};void Pig::climb(){    std::cout << "Pig: I'm climbing!" << std::endl;}// 乌龟子类class Turtle : public Animal{public:    void swim();};void Turtle::swim(){    std::cout << "Turtle: I'm swimming!" << std::endl;}int main(){    Pig pig;    Turtle turtle;    pig.eat();    turtle.eat();    pig.eat(2);    pig.climb();    turtle.swim();    return 0;}

输出：Animal: I'm eating!Animal: I'm eating!Animal: I'm eating 2 foods.Pig: I'm climbing!Turtle: I'm swimming!

样例：为Pig从Animal继承来的方法eat()进行重载（本质是覆盖）；

#include <iostream>#include <string>// 动物基类class Animal{public:    std::string mouth;    void eat();    void sleep();    void drool(); // 流口水};void Animal::eat(){    std::cout << "Animal: I'm eating!" << std::endl;}void Animal::sleep(){    std::cout << "Animal: I'm sleeping!" << std::endl;}void Animal::drool(){    std::cout << "Animal: I'm drooling!" << std::endl;}// 猪子类class Pig : public Animal{public:    void eat(int eatCount);    void climb();};void Pig::eat(int eatCount){    std::cout << "Pig: I'm eating " << eatCount << " foods." << std::endl;}void Pig::climb(){    std::cout << "Pig: I'm climbing!" << std::endl;}// 乌龟子类class Turtle : public Animal{public:    void swim();};void Turtle::swim(){    std::cout << "Turtle: I'm swimming!" << std::endl;}int main(){    Pig pig;    Turtle turtle;    pig.eat(); <span style="color:#ff0000;">// 这里编译出错！！</span>    pig.eat(2);    turtle.eat();    pig.climb();    turtle.swim();    return 0;}

||=== Build: Debug in test_cpp (compiler: GNU GCC Compiler) ===|D:\13....SVNLib\01.Exercise\03.CPP\test_cpp\main.cpp||In function 'int main()':|D:\13....SVNLib\01.Exercise\03.CPP\test_cpp\main.cpp|65|error: no matching function for call to 'Pig::eat()'|D:\13....SVNLib\01.Exercise\03.CPP\test_cpp\main.cpp|65|note: candidate is:|D:\13....SVNLib\01.Exercise\03.CPP\test_cpp\main.cpp|37|note: void Pig::eat(int)|D:\13....SVNLib\01.Exercise\03.CPP\test_cpp\main.cpp|37|note: candidate expects 1 argument, 0 provided|||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|