static.cpp

#include <iostream>
using namespace std;

class InnerClassA
{
  public:
    InnerClassA() { cout << "in create of InnerClassA" << endl; }
};

class InnerClassB
{
  public:
    InnerClassB() { cout << "in create of InnerClassB" << endl; }
    ~InnerClassB() { cout << "in destruction of InnerClassB" << endl; }
};

class WrapperClassA
{
  public:
    WrapperClassA() {}

    InnerClassA &singleton()
    {
        static InnerClassA innerObjA; //local static object
        return innerObjA;
    }
};

// class with non-local static object
class WrapperClassB
{
  public:
    WrapperClassB() {}
    //static data member declaration
    static InnerClassB innerObjB;
};

//static member definition
InnerClassB WrapperClassB::innerObjB;

int main(int argc, char *argv[])
{
    cout << "main() started." << endl;
    WrapperClassA objA;
    objA.singleton();   //只有执行该语句时,innerObjA才被构造出来
    cout << "main() terminated." << endl;
    return 1;
}
// in create of InnerClassB
// main() started.
// in create of InnerClassA
// main() terminated.
// in destruction of InnerClassB