c++++ 中的继承允许创建新类，从基类继承数据和函数；多态通过虚函数和基类指针实现，允许对象根据类型展示不同行为。实战案例展示了继承和多态在银行账户层次结构中的应用，包括储蓄、支票和信用卡账户，每个账户类型都有特定行为，例如存款、取款、支付账单等。

C++ 函数的艺术：继承与多态，对象设计模式之精髓

继承

继承是 C++ 中一种创建新类的方式，新类继承了基类的数据成员和成员函数。语法如下：

立即学习“C++免费学习笔记（深入）”；

class DerivedClass : public BaseClass
{
    // Derived class members
};

多态

多态是对象设计模式的核心，允许对象根据其类型表现出不同的行为。虚函数和基类指针是实现多态的关键。语法如下：

class BaseClass {
public:
    virtual void doSomething() = 0; // 抽象函数
};

class DerivedClass : public BaseClass {
public:
    void doSomething() override {
        // 覆盖基类函数
    }
};

实战案例：多态银行账户

创建一个银行账户层次结构，实现储蓄账户、支票账户和信用卡账户。

#include <iostream>

class BankAccount {
protected:
    double balance;
public:
    virtual double getBalance() const { return balance; }
};

class SavingsAccount : public BankAccount {
public:
    void deposit(double amount) { balance += amount; }
    double withdraw(double amount) {
        if (amount <= balance) {
            balance -= amount;
            return balance;
        }
        return -1; // 提款失败
    }
};

class CheckingAccount : public BankAccount {
public:
    void deposit(double amount) { balance += amount; }
    double withdraw(double amount) {
        if (amount <= balance) {
            balance -= amount;
            return amount;
        }
        return -1; // 提款失败
    }
    bool payBill(double amount) {
        if (amount <= balance) {
            balance -= amount;
            return true;
        }
        return false; // 支付账单失败
    }
};

class CreditCardAccount : public BankAccount {
protected:
    double creditLimit;
public:
    CreditCardAccount(double limit) : creditLimit(limit) {}
    void deposit(double amount) { balance = amount; }
    double withdraw(double amount) {
        if (amount <= balance) {
            balance -= amount;
            return balance;
        } else if (balance + creditLimit >= amount) {
            double overdraft = amount - balance;
            balance = -overdraft;
            return amount;
        }
        return -1; // 提款失败
    }
};

void printBalance(BankAccount& account) {
    std::cout << "Balance: " << account.getBalance() << std::endl;
}

int main() {
    SavingsAccount savings;
    CheckingAccount checking;
    CreditCardAccount credit(1000);

    savings.deposit(500);
    savings.withdraw(200);
    printBalance(savings);

    checking.deposit(1000);
    checking.withdraw(800);
    checking.payBill(300);
    printBalance(checking);

    credit.deposit(200);
    credit.withdraw(500);
    printBalance(credit);

    return 0;
}

在这个示例中，继承和多态被用于创建银行账户层次结构，其中每个账户类型都有不同的行为。调用基类函数 getBalance() 和 printBalance() 可以为所有账户类型一致地获取和打印余额。