singleton 单例模式

#include <iostream>
using namespace std;
class singleton
{
public:
    void method(){ cout <<"singleton::method"<<endl; }
    //...
    static singleton *getInstance();
    static singleton *instance;
private:
    singleton(){}
};

singleton *singleton::instance = NULL;
singleton *singleton::getInstance()
{
    if (instance == NULL)
    {
        instance = new singleton();
    }
    return instance;
}

class singleton2
{
public:
    void method(){ cout <<"singleton2::method"<<endl; }
    static singleton2 *getInstance();

private:
    singleton2(){}
};

singleton2 *singleton2::getInstance()
{
    static singleton2 instance; //线程安全
    return &instance;
}

int main()
{
    singleton *s1 = singleton::getInstance();
    s1->method();
    delete s1;
    singleton2 *s2 = singleton2::getInstance();
    s2->method();
    return 0;
}