linux下如何用C++实现虚拟内存的创建和管理。

#ifndef WIN32

#ifndef SHM_R

#define SHM_R (256)	//共享内存只读

#endif



#ifndef SHM_W	

#define SHM_W (128)	//共享内存只写

#endif



#ifndef SHM_OPEN

#define SHM_OPEN (SHM_R | SHM_W | SHM_R >> 3 | SHM_W >> 3 | SHM_R >> 6 | SHM_W >> 6) //打开共享内存，如果不存在则出错

#endif



#ifndef SHM_CREATE

#define SHM_CREATE (SHM_OPEN | IPC_CREAT)	//建立共享内存，如果已存在则出错

#endif

#include <sys/types.h>

#include <sys/shm.h>

#endif







class yCShm

{

public:

	yCShm ()

	{	

		m_nShmID = 0;

	}

	

	//析构函数

	~yCShm ()

	{

	}

	

public:

	int Create (const char *pIPCName, int nShmSize)

	{

		key_t key = ftok (pIPCName, 0x111);		

		if (key < 0)

		{

			printf("create shm 1\r\n");

			return 0;

		}

		

		if ((m_nShmID = shmget (key, nShmSize, SHM_CREATE)) == -1)

		{

			if ((m_nShmID = shmget (key, nShmSize, SHM_OPEN)) == -1)

			{

				m_nShmID = 0;

				printf("create shm 2\r\n");

				return 0;

			}

		}	

		printf("create shm 3\r\n");

		return 1;

	}

	int Drop ()

	{

		if (m_nShmID != 0)

		{

			shmctl (m_nShmID, IPC_RMID, NULL);

			m_nShmID = 0;

		}

		return 1;

	}

	void *Shmat ( const void * pAddr=0, int nFlag=0)

	{

		void *pointer = NULL;

		pointer = (void *) shmat (m_nShmID, pAddr, nFlag);

		if (pointer == ((void *) -1))

			pointer = NULL;

		return pointer;

	}

private:

	int m_nShmID;		//共享内存ID

	char shm_name[50];	//共享内存映射文件名（也就是Create的第一个参数）

};



int main(int argc, char* argv[])

{

	yCShm rshm;

	rshm.Create("./temp",1);

	rshm.Create("./temp",1024*1024);

	void *p=rshm.Shmat(0,0);

	if(p)

	{

		printf("create shm succ\r\n");

	}

	else

	{

		printf("create shm fail\r\n");

	}

	getchar();

	rshm.Drop();

	return 0;

}