Question

我是编程的新手，我正在尝试使该类单例化的程序。这是制作类单例的正确方法吗？

#include <iostream>
using namespace std;
class Singleton
{
private:
    static bool instanceFlag;
    static Singleton *single;
public:
    static Singleton* getInstance();
    void method();
    ~Singleton()
    {
        instanceFlag = false;
    }
};
bool Singleton::instanceFlag = false;
Singleton* Singleton::single = NULL;
Singleton* Singleton::getInstance()
{
    if(! instanceFlag)
    {
        single = new Singleton();
        instanceFlag = true;
        return single;
    }
    else
    {
        return single;
    }
}
void Singleton::method()
{
    cout << "Method of the singleton class";
}
int main()
{
    Singleton *sc1,*sc2;
    sc1 = Singleton::getInstance();
    sc1->method();
    sc2=Singleton::getInstance();
    sc2->method();
    return 0;
}

这是制作班级单身的正确方法吗？

Answer 1

你的事情过于复杂。试试Scott Meyers的单身人士：

struct SingletonClass {
    // instance() function return a reference
    static SingletonClass& instance() {
        // static local variable are initialized one time.
        static SingletonClass inst;

        // We return the instance, which is the same for every calls.
        return inst;
    }

private:
    // Private since we don't want other class to create instances
    SingletonClass() = default;

    // Our class is not copiable or movable
    SingletonClass(const SingletonClass&) = delete;
    SingletonClass(SingletonClass&&) = delete;
    SingletonClass& operator=(const SingletonClass&) = delete;
    SingletonClass& operator=(SingletonClass&&) = delete;
};

您可以像这样使用您的课程：

auto& myInstance = SingletonClass::instance();

奖励：它不使用动态分配，它是线程安全的，而且更简单。

Answer 2

试试这个解决方案：

class Singleton {
private:
    static Singleton* instance;
    Singleton() {}  // must be private
public:
    static Singleton* getInstance() {
        if (instance == NULL)
            instance = new Singleton();
        return instance;
    }
    void method() { cout << "Method of the singleton class\n"; }
};
Singleton* Singleton::instance = NULL;

这是制作班级单身人士的正确程序吗？

2 个答案: