设计一个含有两个私有变量的引用计数类，然后实现一个KString类，用这个引用计数类实现写时拷贝

以下是一个可能的实现：

#include <string>
#include <iostream>

class RefCount {
private:
    int count;
    int weakCount;
public:
    RefCount() : count(0), weakCount(0) {}
    void addRef() { count++; }
    void release() { count--; if (count == 0) delete this; }
    void addWeakRef() { weakCount++; }
    void releaseWeak() { weakCount--; if (weakCount == 0 && count == 0) delete this; }
};

class KString {
private:
    std::string* str;
    RefCount* refCount;
public:
    KString() : str(new std::string()), refCount(new RefCount()) { refCount->addRef(); }
    KString(const char* s) : str(new std::string(s)), refCount(new RefCount()) { refCount->addRef(); }
    KString(const std::string& s) : str(new std::string(s)), refCount(new RefCount()) { refCount->addRef(); }
    KString(const KString& other) : str(other.str), refCount(other.refCount) { refCount->addRef(); }
    ~KString() { refCount->release(); }
    KString& operator=(const KString& other) {
        if (this != &other) {
            refCount->release();
            str = other.str;
            refCount = other.refCount;
            refCount->addRef();
        }
        return *this;
    }
    char& operator[](int i) {
        if (refCount->count > 1) {
            refCount->release();
            str = new std::string(*str);
            refCount = new RefCount();
            refCount->addRef();
        }
        return (*str)[i];
    }
    const char& operator[](int i) const {
        return (*str)[i];
    }
};

int main() {
    KString s1("hello");
    KString s2 = s1;
    std::cout << s1[1] << std::endl; // 'e'
    std::cout << s2[1] << std::endl; // 'e'
    s1[1] = 'a';
    std::cout << s1[1] << std::endl; // 'a'
    std::cout << s2[1] << std::endl; // 'e'
    return 0;
}

这个实现中，KString类包含一个指向std::string的指针和一个指向RefCount的指针。RefCount类用于记录当前对象的引用计数和弱引用计数，当引用计数为0时会自动删除对象。KString类的默认构造函数和带参构造函数会创建一个新的std::string对象和一个新的RefCount对象，并将引用计数加一。拷贝构造函数和赋值运算符会将指针和引用计数从另一个KString对象复制过来，并将引用计数加一。KString类还重载了[]运算符，当引用计数大于1时会进行写时拷贝，即复制一个新的std::string对象并将引用计数设为1，然后再进行修改。这样可以确保只有当一个KString对象确实需要修改时才会进行拷贝，从而避免了不必要的性能开销。