多态分为两类
- 静态多态:函数重载 和 运算符重载属于静态多态,复用函数名
- 动态多态:派生类和虚函数实现运行时多态
静态多态和动态多态区别:
- 静态多态的函数地址早绑定 - 编译阶段确定函数地址
- 动态多态的函数地址晚绑定 - 运行阶段确定函数地址
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| #include <iostream>
using namespace std;
class Animal { public: virtual void speak() { cout << "动物在说话" << endl; } };
class Cat :public Animal { public: void speak() { cout << "miao miao miao" << endl; } };
void doSpeak(Animal &animal) { animal.speak(); }
void test01() { Cat cat; doSpeak(cat); }
int main() { test01(); }
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总结:
多态满足条件
多态使用条件
重写:函数返回值类型 函数名 参数列表 完全一致称为重写
虚表
还是上面的例子,打印一下 sizeof(animal)
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| Animal animal; cout << sizeof(animal) << endl; // 8
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是因为,class Animal
中有一个 vfptr
指针指向 vftable
vfptr
是指虚函数指针,指向 vftable
虚函数表
- v - virtual
- f - function
- ptr - pointer
当子类重写父类的虚函数
子类中的虚函数表内部会替换成子类的虚函数地址
使用多态的例子
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| #include <iostream> #include <string>
using namespace std;
class Calculator { public:
int getResult(string oper) { if (oper == "+") { return m_Num1 + m_Num2; } else if (oper == "-") { return m_Num1 - m_Num2; } else if (oper == "*") { return m_Num1 * m_Num2; } return -1; } int m_Num1; int m_Num2; };
class AbstractCalculator { public: virtual int getResult() = 0; int m_Num1, m_Num2; };
class AddCalculator :public AbstractCalculator { public: int getResult() { return m_Num1 + m_Num2; } };
class SubCalculator :public AbstractCalculator { public: int getResult() { return m_Num1 - m_Num2; } };
class MulCalculator :public AbstractCalculator { public: int getResult() { return m_Num1 * m_Num2; } };
void test01() { Calculator c; c.m_Num1 = 10; c.m_Num2 = 10;
cout << c.m_Num1 << " + " << c.m_Num2 << " = " << c.getResult("+") << endl;
cout << c.m_Num1 << " - " << c.m_Num2 << " = " << c.getResult("-") << endl;
cout << c.m_Num1 << " * " << c.m_Num2 << " = " << c.getResult("*") << endl;
}
void test02() { AbstractCalculator * abc = new AddCalculator(); abc->m_Num1 = 100; abc->m_Num2 = 100; cout << abc->m_Num1 << " + " << abc->m_Num2 << " = " << abc->getResult() << endl; delete(abc);
abc = new SubCalculator(); abc->m_Num1 = 100; abc->m_Num2 = 100; cout << abc->m_Num1 << " - " << abc->m_Num2 << " = " << abc->getResult() << endl; }
int main() { test01(); test02(); }
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多态好处:
- 组织结构清晰
- 可读性强
- 对于前期和后期扩展以及维护性高