单件类运行时错误问题。。代码很短。。路过好心人帮帮忙

[baomaxiangche852]

单件类问题。。路过的大大帮帮忙啊~~~

写一个单件类，编译通过运行时提示：
1>------ 已启动生成: 项目: 单件类, 配置: Debug Win32 ------
1>正在链接...
1>main.obj : error LNK2001: 无法解析的外部符号 "protected: static class A * Singleton<class A>::ms_Singleton" (?ms_Singleton@?$Singleton@VA@@@@1PAVA@@A)
1>E:\程序\数据结构与STL复习\单件类\Debug\单件类.exe : fatal error LNK1120: 1 个无法解析的外部命令
1>生成日志保存在“file://e:\程序\数据结构与STL复习\单件类\单件类\Debug\BuildLog.htm”
1>单件类 - 2 个错误，0 个警告
========== 生成: 0 已成功, 1 已失败, 0 最新, 0 已跳过 ==========


代码

#include <assert.h>
template <typename T> 
class Singleton
{
//private:
	/** \brief Explicit private copy constructor. This is a forbidden operation.*/
	Singleton(const Singleton<T> &);

	/** \brief Private operator= . This is a forbidden operation. */
	Singleton& operator=(const Singleton<T> &);

protected:

	static T* ms_Singleton;

public:
	Singleton( void )
	{
		assert( !ms_Singleton );
		ms_Singleton = static_cast< T* >( this );

	}
	~Singleton( void )
	{  assert( ms_Singleton );  ms_Singleton = 0;  }
	static T& getSingleton( void )
	{	assert( ms_Singleton );  return ( *ms_Singleton ); }
	static T* getSingletonPtr( void )
	{ return ms_Singleton; }
};

class A:public Singleton<A>
{

};

int main()
{
	A* a1=new A();
	A* a2=new A();
	return 1;
}

[turing-complete]

亲，你这个是个链接错误，原因是没有初始化静态成员变量。

#include <cassert>

template<typename T>
class Singleton {
//private:
    /** \brief Explicit private copy constructor. This is a forbidden operation.*/
    Singleton(const Singleton<T> &);

    /** \brief Private operator= . This is a forbidden operation. */
    Singleton& operator=(const Singleton<T> &);

protected:

    static T* ms_Singleton;

public:
    Singleton(void) {
        assert( !ms_Singleton);
        ms_Singleton = static_cast<T*>(this);

    }
    ~Singleton(void) {
        assert( ms_Singleton);
        ms_Singleton = 0;
    }
    static T& getSingleton(void) {
        assert( ms_Singleton);
        return (*ms_Singleton);
    }
    static T* getSingletonPtr(void) {
        return ms_Singleton;
    }
};

template<typename T>
T* Singleton::ms_Singleton = NULL;

class A: public Singleton<A> {

};

int main() {
    A* a1 = new A();
    A* a2 = new A();
    return 1;
}

[惬意]

把你的类定义完之后再定义成员函数