C++ 单例模式

#include <stdio.h>
class aaa
{
public:
    static aaa* GetInstance()
    {
        if (m_instance == NULL)
        {
            m_instance = new aaa();
        }
        return m_instance;
    }

private:
    aaa(){};
    static aaa* m_instance;
};
aaa* aaa::m_instance = NULL;

int main()
{
    aaa* a = aaa::GetInstance();
    aaa* b = aaa::GetInstance();
    return 0;
}