张宗平
b89819d5db
大纲按「3天C++强化(含OOP)+1天Qt桌面」组织，讲:练≈1:2.7；每个知识点直接 链接仓库真实代码文件与 ERRATA/VERSION_NOTES 里记录的具体坑。幻灯片 vendor 了 reveal.js 5.2.1（核心+highlight插件），零 CDN 依赖，配 serve.py 本地起服务（仅绑定 127.0.0.1）供离线播放，代码链接可点开查看源码。
312 lines
14 KiB
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312 lines
14 KiB
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<!DOCTYPE html>
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<html lang="zh-CN">
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<meta charset="utf-8">
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<title>Day 2 · OOP 进阶</title>
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<body>
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<div class="reveal">
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<div class="slides">
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<section>
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<h1>Day 2</h1>
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<h3>OOP 进阶</h3>
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<p class="module-badge">Qt 方向实训 · 第 2 / 4 天 · 讲:练 ≈ 1:2.7</p>
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<ul>
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<li>模块 A（3 课时）：对象模型 / 友元 / 运算符重载</li>
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<li>模块 B（3 课时）：继承与多态</li>
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</ul>
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<p><small>回顾：Day1 已建立类/构造析构/深浅拷贝的直觉——今天在这个基础上深挖机制</small></p>
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</section>
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<!-- ===================== 模块 A：讲 ===================== -->
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<section>
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<section>
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<p class="module-badge">模块 A · 讲授 35min</p>
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<h2>对象模型 / 友元 / 运算符重载 <span class="tag tag-lecture">讲</span></h2>
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<ul>
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<li>this 指针到底解决什么问题</li>
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<li>友元：突破封装的代价与取舍</li>
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<li>运算符重载：=、==、[]、()、++/-- 全景</li>
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</ul>
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</section>
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<section>
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<h3>this 指针：区分同名 + 隐式参数 <span class="tag tag-lecture">讲</span></h3>
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<pre><code class="cpp" data-trim data-noescape>
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class Person{
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public:
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Person(string name, int age){
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this->name = name; // 形参名与成员名相同，靠 this-> 区分
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this->age = age;
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}
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// 成员函数隐含的第一个参数就是 this —— operator= 也是这样实现的
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Person PersonPlusPerson(Person& person){
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string newname = this->name + person.name;
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int newage = this->age + person.age;
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return Person(newname, newage);
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}
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};
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</code></pre>
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<p><small>出处：<a class="filelink" target="_blank"
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href="../../../p01/ch04/s04/this_pointer.cpp">p01/ch04/s04/this_pointer.cpp</a></small></p>
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</section>
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<section>
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<h3>友元：全局函数 / 成员函数 / 整个类 <span class="tag tag-lecture">讲</span></h3>
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<pre><code class="cpp" data-trim data-noescape>
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class Building{
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friend void CleanBedRoom(Building& building); // 友元全局函数
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friend class MyFriend; // 友元类——MyFriend 的所有成员都能访问私有区
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public:
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Building();
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private:
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string mBedroom;
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};
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</code></pre>
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<p><small>友元是「单向」「不可传递」「不可继承」的特权授予——用得越多，封装边界越模糊，
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权衡取舍要讲清楚。出处：<a class="filelink" target="_blank"
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href="../../../p01/ch04/s05/friend_syntax.cpp">p01/ch04/s05/friend_syntax.cpp</a></small></p>
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</section>
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<section>
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<h3>赋值运算符重载：与拷贝构造的分工 <span class="tag tag-lecture">讲</span></h3>
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<pre><code class="cpp" data-trim data-noescape>
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Person2& operator=(const Person2& person){
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// 关键：当前对象已存在，pName 可能已指向堆内存——必须先释放，否则内存泄漏
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if (this->pName != NULL){ delete[] this->pName; }
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this->pName = new char[strlen(person.pName) + 1];
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strcpy(this->pName, person.pName);
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return *this; // 返回引用才能支持 a = b = c 连续赋值
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}
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</code></pre>
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<p><small>“初始化用拷贝构造，已存在对象再赋值用 operator=”——这条分界线是本节强化重点。
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出处：<a class="filelink" target="_blank"
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href="../../../p01/ch04/s06/overload_assignment.cpp">p01/ch04/s06/overload_assignment.cpp</a></small></p>
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</section>
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<section>
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<h3>前置/后置 ++ 的重载差异 <span class="tag tag-lecture">讲</span></h3>
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<pre><code class="cpp" data-trim data-noescape>
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Complex& operator++(){ // 前置++：改自身，返回引用
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mA++; mB++;
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return *this;
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}
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Complex operator++(int){ // 后置++：占位 int 参数只是为了和前置区分重载签名
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Complex temp = *this; // 必须先拷贝旧值
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mA++; mB++;
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return temp; // 返回值（而非引用）——所以后置++开销更大
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}
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</code></pre>
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<p><small>出处：<a class="filelink" target="_blank"
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href="../../../p01/ch04/s06/overload_increment_decrement.cpp">p01/ch04/s06/overload_increment_decrement.cpp</a></small></p>
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</section>
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</section>
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<!-- ===================== 模块 A：练 ===================== -->
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<section>
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<section>
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<p class="module-badge">模块 A · 练习 95min</p>
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<h2>动手：运算符重载 <span class="tag tag-practice">练</span></h2>
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</section>
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<section>
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<div class="task-card">
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<h4>任务卡 1 · operator= + operator== <span class="tag tag-practice">练</span></h4>
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<p>给 Day1 写的类（或新写一个含指针成员的类）实现 <code>operator=</code>（注意先
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释放旧资源）与 <code>operator==</code>，参照
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<a class="filelink" target="_blank" href="../../../p01/ch04/s06/overload_assignment.cpp">overload_assignment.cpp</a>、
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<a class="filelink" target="_blank" href="../../../p01/ch04/s06/overload_equality.cpp">overload_equality.cpp</a>。</p>
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</div>
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</section>
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<section>
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<div class="task-card">
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<h4>任务卡 2 · operator[] 边界检查 <span class="tag tag-practice">练</span></h4>
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<p>实现一个重载了 <code>operator[]</code> 的简单容器类（固定大小数组包装），
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越界访问要有明确行为（断言或抛异常），参照
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<a class="filelink" target="_blank" href="../../../p01/ch04/s06/overload_pointer_operator.cpp">overload_pointer_operator.cpp</a> 的思路。</p>
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</div>
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</section>
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<section>
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<div class="task-card">
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<h4>任务卡 3 · 选做：友元实现 operator<< <span class="tag tag-practice">练</span></h4>
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<p>参照 <a class="filelink" target="_blank"
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href="../../../p01/ch04/s06/overload_with_friend.cpp">overload_with_friend.cpp</a>，
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为你的类实现 <code>friend ostream& operator<<</code>，讨论「为什么流输出运算符
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通常不能写成成员函数」（提示：左操作数是 ostream，不是本类对象）。</p>
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</div>
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</section>
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</section>
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<!-- ===================== 模块 B：讲 ===================== -->
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<section>
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<section>
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<p class="module-badge">模块 B · 讲授 35min</p>
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<h2>继承与多态 <span class="tag tag-lecture">讲</span></h2>
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<ul>
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<li>继承中构造/析构的顺序</li>
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<li>同名成员遮蔽 vs 重写</li>
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<li>虚继承解决菱形问题</li>
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<li>upcast 裁切问题 → virtual 解决</li>
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<li>纯虚函数/抽象类、虚析构的意义</li>
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</ul>
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</section>
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<section>
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<h3>构造先基类后派生类，析构相反 <span class="tag tag-lecture">讲</span></h3>
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<pre><code class="cpp" data-trim data-noescape>
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class A{ public: A(){cout<<"A构造\n";} ~A(){cout<<"A析构\n";} };
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class B : public A{ public: B(){cout<<"B构造\n";} ~B(){cout<<"B析构\n";} };
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class C : public B{ public: C(){cout<<"C构造\n";} ~C(){cout<<"C析构\n";} };
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int main(){ C c; }
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// 输出顺序：A构造 → B构造 → C构造 → C析构 → B析构 → A析构
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</code></pre>
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<p><small>出处：<a class="filelink" target="_blank"
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href="../../../p01/ch04/s07/inheritance_ctor_dtor_order.cpp">p01/ch04/s07/inheritance_ctor_dtor_order.cpp</a></small></p>
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</section>
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<section>
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<h3>同名成员：默认遮蔽，需类名限定 <span class="tag tag-lecture">讲</span></h3>
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<pre><code class="cpp" data-trim data-noescape>
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class Base{ public: Base():mParam(0){} int mParam; };
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class Derived : public Base{
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public:
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Derived():mParam(10){}
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void Print(){
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cout << Base::mParam << endl; // 必须类名限定才能访问被遮蔽的基类成员
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cout << mParam << endl; // 默认访问派生类自己的
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}
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int mParam;
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};
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</code></pre>
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<p><small>出处：<a class="filelink" target="_blank"
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href="../../../p01/ch04/s07/same_name_members.cpp">p01/ch04/s07/same_name_members.cpp</a></small></p>
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</section>
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<section>
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<h3>菱形继承 → 虚继承 <span class="tag tag-lecture">讲</span></h3>
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<pre><code class="cpp" data-trim data-noescape>
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class BigBase{ public: int mParam; };
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class Base1 : public BigBase{};
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class Base2 : public BigBase{};
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class Derived : public Base1, public Base2{};
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// derived.mParam 二义——两份 BigBase 子对象；须写 derived.Base1::mParam 消歧义
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// 虚继承（public virtual BigBase）能让两条路径共享同一份 BigBase 子对象
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</code></pre>
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<p><small>出处：<a class="filelink" target="_blank"
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href="../../../p01/ch04/s07/diamond_virtual_inheritance.cpp">diamond_virtual_inheritance.cpp</a>
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及 <a class="filelink" target="_blank"
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href="../../../p01/ch04/s07/diamond_virtual_inheritance_2.cpp">_2.cpp</a>（虚继承版本对比）</small></p>
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</section>
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<section>
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<h3>upcast 裁切问题：不加 virtual 就没有多态 <span class="tag tag-lecture">讲</span></h3>
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<pre><code class="cpp" data-trim data-noescape>
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// 问题版：Animal::speak_1 不是 virtual
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class Animal{ public: void speak_1(){ cout<<"动物在唱歌...\n"; } };
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class Dog : public Animal{ public: void speak_1(){ cout<<"小狗在唱歌...\n"; } };
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void DoBussiness(Animal& animal){ animal.speak_1(); }
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void test(){ Dog dog; DoBussiness(dog); } // 输出「动物在唱歌」——静态绑定，不是想要的结果
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// 解决版：都加 virtual → 动态绑定，输出「小狗在唱歌」
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</code></pre>
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<p><small>问题版出处：<a class="filelink" target="_blank"
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href="../../../p01/ch04/s08/upcast_problem.cpp">upcast_problem.cpp</a>；解决版：
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<a class="filelink" target="_blank"
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href="../../../p01/ch04/s08/virtual_function_solution.cpp">virtual_function_solution.cpp</a></small></p>
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</section>
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<section>
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<h3>纯虚函数、抽象类、虚析构的意义 <span class="tag tag-lecture">讲</span></h3>
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<pre><code class="cpp" data-trim data-noescape>
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class People{
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public:
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virtual void showName() = 0; // 纯虚函数 → People 是抽象类，不能实例化
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virtual ~People(){ cout<<"析构 People\n"; } // 虚析构：基类指针 delete 派生类对象时能正确调用派生类析构
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};
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class Worker : public People{
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public:
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virtual void showName(){ /* ... */ }
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~Worker(){ cout<<"析构 Worker\n"; delete[] pName; }
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private:
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char* pName;
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};
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People* p = new Worker;
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delete p; // 若 ~People() 不是 virtual，只会调用 ~People，Worker::pName 泄漏
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</code></pre>
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<p><small>强化点：<code class="filelink">ERRATA.md [58954469:5] abstract-instantiation</code>
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——wiki 原文一度把带纯虚析构的类直接实例化，这是编译错误。出处：
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<a class="filelink" target="_blank" href="../../../p01/ch04/s08/pure_virtual_dtor.cpp">pure_virtual_dtor.cpp</a>、
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<a class="filelink" target="_blank" href="../../../p01/ch04/s08/virtual_dtor_purpose.cpp">virtual_dtor_purpose.cpp</a></small></p>
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</section>
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</section>
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<!-- ===================== 模块 B：练 ===================== -->
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<section>
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<section>
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<p class="module-badge">模块 B · 练习 95min</p>
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<h2>动手：继承与多态 <span class="tag tag-practice">练</span></h2>
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</section>
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<section>
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<div class="task-card">
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<h4>任务卡 1 · 复现并修复 upcast 裁切 <span class="tag tag-practice">练</span></h4>
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<p>先跑 <a class="filelink" target="_blank"
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href="../../../p01/ch04/s08/upcast_problem.cpp">upcast_problem.cpp</a> 观察输出，
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再手动加 <code>virtual</code> 关键字重新编译，对比两次输出差异，写清楚“静态绑定 vs 动态绑定”
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各自发生在什么时候。</p>
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</div>
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</section>
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<section>
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<div class="task-card">
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<h4>任务卡 2 · 基类指针管理派生类对象 <span class="tag tag-practice">练</span></h4>
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<p>设计一个含虚析构的基类 + 2 个派生类（各自持有一个堆内存成员），用基类指针数组
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管理多个对象，逐个 <code>delete</code>，通过析构函数里的打印验证：(1) 调用的是派生类
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析构 (2) 没有内存泄漏（可用打印计数或 valgrind 验证）。</p>
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</div>
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</section>
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<section>
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<div class="task-card">
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<h4>任务卡 3 · 选做：普通继承 vs 虚继承对比 <span class="tag tag-practice">练</span></h4>
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<p>对照 <a class="filelink" target="_blank"
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href="../../../p01/ch04/s07/diamond_virtual_inheritance.cpp">diamond_virtual_inheritance.cpp</a>
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与 <a class="filelink" target="_blank"
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href="../../../p01/ch04/s07/diamond_virtual_inheritance_2.cpp">_2.cpp</a>，
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打印 <code>sizeof(Derived)</code> 并解释两种继承方式下对象体积差异的原因。</p>
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</div>
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</section>
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</section>
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<!-- ===================== 收尾 ===================== -->
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<section>
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<h2>当日产出验证</h2>
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<div class="verify-box">
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<h4>验收标准</h4>
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<pre><code class="bash" data-trim>cmake --build build --target all_p01_ch04_s06
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cmake --build build --target all_p01_ch04_s07
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cmake --build build --target all_p01_ch04_s08</code></pre>
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<p>全绿；产出「基类指针管理派生类对象、正确释放」的可运行小程序。</p>
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</div>
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<p class="footer-note"><small>明日预告：Day 3 —— 泛型与标准库（模板 / 类型转换 /
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异常 / IO 流 / STL）</small></p>
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<p><a class="filelink" href="index.html">返回目录</a></p>
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