编辑“︁C++ 享元模式”︁（章节）

== 代码示例 ==  
以下示例展示如何用享元模式优化文本编辑器中的字符渲染：  

<syntaxhighlight lang="cpp">  
#include <iostream>  
#include <unordered_map>  
#include <string>  

// 享元接口  
class Character {  
public:  
    virtual void display(int position) = 0;  
    virtual ~Character() = default;  
};  

// 具体享元类  
class ConcreteCharacter : public Character {  
private:  
    char symbol_;  // 内在状态（可共享）  
public:  
    explicit ConcreteCharacter(char symbol) : symbol_(symbol) {}  

    void display(int position) override {  // 外在状态由参数传递  
        std::cout << "Character '" << symbol_ << "' at position " << position << std::endl;  
    }  
};  

// 享元工厂  
class CharacterFactory {  
private:  
    std::unordered_map<char, Character*> characters_;  

public:  
    Character* getCharacter(char key) {  
        if (characters_.find(key) == characters_.end()) {  
            characters_[key] = new ConcreteCharacter(key);  
        }  
        return characters_[key];  
    }  

    ~CharacterFactory() {  
        for (auto& pair : characters_) {  
            delete pair.second;  
        }  
    }  
};  

// 客户端代码  
int main() {  
    CharacterFactory factory;  

    // 模拟文本中的字符  
    std::string text = "Hello, Flyweight!";  
    for (int i = 0; i < text.size(); ++i) {  
        Character* character = factory.getCharacter(text[i]);  
        character->display(i);  // 位置是外在状态  
    }  

    return 0;  
}  
</syntaxhighlight>  

=== 输出示例 ===  
<pre>  
Character 'H' at position 0  
Character 'e' at position 1  
Character 'l' at position 2  
Character 'l' at position 3  
Character 'o' at position 4  
...  
</pre>  

=== 代码解析 ===  
1. '''ConcreteCharacter''' 存储内在状态（如字符符号），而外在状态（如位置）通过参数传递。  
2. '''CharacterFactory''' 确保相同字符仅创建一个实例。  
3. 客户端通过工厂获取享元对象，避免重复创建。