C tutorial covering inheritance and polymorphism
Jul 02, 2025 am 01:23 AM
C++的繼承和多態(tài)是面向?qū)ο缶幊痰暮诵臋C(jī)制。1. 繼承允許基于已有類創(chuàng)建新類，實現(xiàn)代碼復(fù)用與層次結(jié)構(gòu)設(shè)計，需注意訪問控制符、構(gòu)造函數(shù)調(diào)用及避免過度繼承；2. 多態(tài)通過虛函數(shù)實現(xiàn)，使基類指針或引用可調(diào)用派生類方法，應(yīng)用包括圖形界面、插件系統(tǒng)等，但需關(guān)注性能開銷、虛析構(gòu)函數(shù)及正確使用override關(guān)鍵字；3. 典型問題如基類未定義虛析構(gòu)函數(shù)導(dǎo)致delete時未調(diào)用派生類析構(gòu)，以及虛函數(shù)覆蓋錯誤，可通過設(shè)置虛析構(gòu)和添加override修復(fù)。掌握這兩個特性有助于理解并應(yīng)用多種設(shè)計模式，并提升大型項目中類結(jié)構(gòu)的設(shè)計能力。
C++的繼承和多態(tài)是面向?qū)ο缶幊痰暮诵膬?nèi)容，理解這兩個概念能幫助你寫出結(jié)構(gòu)清晰、可擴(kuò)展性強(qiáng)的代碼。這篇文章不會從頭講類的基礎(chǔ)知識，而是聚焦在繼承怎么用、多態(tài)為什么重要，以及實際開發(fā)中容易踩坑的地方。
繼承：代碼復(fù)用的基礎(chǔ)方式
繼承允許我們基于一個已有的類（稱為基類或父類）創(chuàng)建新的類（派生類或子類），從而實現(xiàn)代碼復(fù)用和層次結(jié)構(gòu)的設(shè)計。
- 派生類可以訪問基類的 public 和 protected 成員
- 可以重寫基類中的方法，也可以添加新功能
- 支持單繼承和多繼承，但多繼承容易帶來復(fù)雜性，慎用
舉個簡單的例子：
class Animal {
public:
void eat() { cout << "Animal is eating." << endl; }
};
class Dog : public Animal {
public:
void bark() { cout << "Dog is barking." << endl; }
};上面的例子中，Dog 類繼承了 Animal 類的功能，并在此基礎(chǔ)上增加了自己的方法。
使用繼承時要注意幾點(diǎn)：
- 訪問控制符（public / protected / private）會影響成員的可見性
- 如果基類有構(gòu)造函數(shù)，派生類需要通過初始化列表調(diào)用它
- 避免過度繼承，保持類之間的邏輯清晰
多態(tài)：運(yùn)行時決定行為的關(guān)鍵機(jī)制
多態(tài)指的是同一個接口可以有不同的實現(xiàn)方式。在 C++ 中，主要是通過虛函數(shù)（virtual functions）來實現(xiàn)的。
當(dāng)你想讓基類指針或引用調(diào)用派生類的方法時，必須將該方法聲明為虛函數(shù)。
示例：
class Shape {
public:
virtual void draw() { cout << "Drawing a shape." << endl; }
};
class Circle : public Shape {
public:
void draw() override { cout << "Drawing a circle." << endl; }
};在這個例子中，如果使用 Shape* 指向 Circle 對象并調(diào)用 draw()，會執(zhí)行 Circle 的版本，前提是 draw() 是虛函數(shù)。
多態(tài)常見應(yīng)用場景包括：
- 圖形界面事件處理
- 插件系統(tǒng)或策略模式設(shè)計
- 游戲中不同角色的行為管理
需要注意：
- 虛函數(shù)帶來一定的性能開銷（虛函數(shù)表）
- 不要忘記將析構(gòu)函數(shù)設(shè)為虛函數(shù)，否則可能造成內(nèi)存泄漏
- 使用
override關(guān)鍵字有助于避免覆蓋錯誤
繼承與多態(tài)結(jié)合使用的典型問題
在實際項目中，很多人會遇到“delete 基類指針導(dǎo)致未定義行為”的情況。這通常是因為基類沒有虛析構(gòu)函數(shù)。
比如下面這段代碼就有風(fēng)險：
class Base {
public:
~Base() {} // 非虛析構(gòu)函數(shù)
};
class Derived : public Base {
public:
~Derived() { /* 資源釋放 */ }
};
Base* obj = new Derived();
delete obj; // 不會調(diào)用 Derived 的析構(gòu)函數(shù)！修復(fù)辦法很簡單：只要把基類的析構(gòu)函數(shù)設(shè)為虛函數(shù)即可。
另一個常見問題是虛函數(shù)覆蓋不正確，比如參數(shù)不同或者拼寫錯誤。這時候加上 override 就能被編譯器及時發(fā)現(xiàn)。
基本上就這些。掌握好繼承和多態(tài)之后，你會發(fā)現(xiàn)很多設(shè)計模式都建立在這兩個機(jī)制之上。雖然語法不算太難，但真正用好還是得多實踐，尤其是在大型項目中如何合理設(shè)計類層次的問題。
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