Is this a good Singleton implementation? Is there anything I should be aware of? If so, how can it be improved?template <class T>class Singleton{public:    static T& getInstance()    {        static T instance;        return instance;    }protected:    Singleton() {}    ~Singleton() {}private:    Singleton(Singleton const&);    void operator=(Singleton const&);};Usage example:#include <stdio.h>class A : public Singleton<A> {public:    A() {        a = 100;    }    int get_a() { return a; }    void set_a(int v) { a = v;  }private:    int a;};A& s = A::getInstance();void free1() {    printf(%d\n, s.get_a());}void free2() {    s.set_a(200);}void free3() {    printf(--> %d, s.get_a());}void main() {    free1();    free2();    free3();}Let's consider an alternative to avoid the usage of Singletons, instead having:class A : public Singleton<A>let's say it becomes:class Aand let's say we define a global variable:A g_s = A();and then this global variable will be accessed by other files using external, would that bring some sort of benefit?external A g_s;
C++ singleton using templates
c++;singleton