笔试题（1）

1.类实例化一次

class A{ public: static A * GetInstance() { if (NULL == _instance) _instance = new A(); return _instance; } private: A(){}//构造 static A *_instance;};//初始化静态变量A *A::_instance = NULL;

2.进程通信

3.进程同步

4.模板特例