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Virtual function and pure virtual function
concept
First: Emphasize a concept
Defining a function as a virtual function does not mean that the function is a function that is not implemented.
Defining it as a virtual function is to allow the pointer of the base class to call this function of the subclass.
Defining a function as a pure virtual function means that the function has not been implemented.
The purpose of defining a pure virtual function is to implement an interface and act as a specification. Programmers who inherit this class from the specification must implement this function.
Normal counter
Normal counter
class Calculator
{
public:
void setv1(int v)
{
this->val1 = v;
}
void setv2(int v)
{
this->val2 = v;
}
int getResult(string oper)
{
if (oper == "+")
{
return val1 + val2;
}
else if (oper == "-")
{
return val1 - val2;
}
}
private:
int val1;
int val2;
};
void test01()
{
Calculator cal;
cal.setv1(10);
cal.setv2(10);
cout << cal.getResult("+") << endl;
cout << cal.getResult("-") << endl;
}
Polymorphic calculator
In real development, there is a development principle that is open and closed .
- Open to expansion
- Close to modification
Polymorphic calculator code
#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
//利用多态实现计算器
class abstractCalculator
{
public:
//虚函数 virtual int getResult(){ return 0; };
//纯虚函数
//如果父类中有了 纯虚函数 子类继承父类，就必须要实现 纯虚函数
//如果父类中 有了 纯虚函数 ，这个父类 就无法实例化对象了
//这个类有了纯虚函数，通常又称为 抽象类
virtual int getResult() = 0;
void setv1(int v)
{
this->val1 = v;
}
void setv2(int v)
{
this->val2 = v;
}
public:
int val1;
int val2;
};
//如果父类中有了 纯虚函数 子类继承父类，就必须要实现 纯虚函数
class A :public abstractCalculator
{
public:
virtual int getResult()
{
return 0;
}
};
//加法计算器
class PlusCalculator :public abstractCalculator
{
public:
virtual int getResult()
{
return val1 + val2;
};
};
class SubCalculator : public abstractCalculator
{
public:
virtual int getResult()
{
return val1 - val2;
};
};
class ChengCalculator :public abstractCalculator
{
public:
virtual int getResult()
{
return val1 * val2;
};
};
void test02()
{
abstractCalculator* abc;
//加法计算器
abc = new PlusCalculator;
abc->setv1(10);
abc->setv2(20);
cout << abc->getResult() << endl;
delete abc;
abc = new SubCalculator;
abc->setv1(10);
abc->setv2(20);
cout << abc->getResult() << endl;
delete abc;
abc = new ChengCalculator;
abc->setv1(10);
abc->setv2(20);
cout << abc->getResult() << endl;
//如果父类有了纯虚函数，不能实例化对象了
//abstractCalculator aaa;
//abstractCalculator * abc = new abstractCalculator;
}
int main() {
//test01();
test02();
system("pause");
return EXIT_SUCCESS;
}
Among them, virtual int getResult(){ return 0; };is a virtual function, virtual int getResult() = 0;is a pure virtual function.
other
The difference between virtual function and pure virtual function