访问类的静态成员变量的时候出现undefined reference to

Question

#include <iostream>using namespace std;class CSingleton{//其他成员public:static CSingleton* GetInstance();int age;private:CSingleton(){};static CSingleton* m_pInstance;};CSingleton* CSingleton::GetInstance(){if ( m_pInstance == NULL ) //判断是否第一次调用m_pInstance = new CSingleton();return m_pInstance;}int main(){CSingleton* p1 = CSingleton::GetInstance();p1->age=10;cout<<p1->age;return 0;}