//共享内存区段的挂载,脱离和使用   

//理解共享内存区段就是一块大内存   

#include <stdio.h>   

#include <sys/shm.h>   

#include <sys/ipc.h>   

#include <errno.h>   

#define MY_SHM_ID 67483   

int main(  )  

    {  

        //共享内存区段的挂载和脱离   

        int shmid,ret;  

        void* mem;  

        shmid=shmget( MY_SHM_ID,0,0 );  

        if( shmid>=0 )  

            {  

                mem=shmat( shmid,( const void* )0,0 );  

                //shmat()返回进程地址空间中指向区段的指针   

                if( ( int )mem!=-1 )  

                    {  

                        printf( "Shared memory was attached in our address space at %p/n",mem );  

                        //向共享区段内存写入数据   

                        strcpy( ( char* )mem,"This is a test string./n" );  

                        printf( "%s/n",(char*)mem );  

                        //脱离共享内存区段   

                        ret=shmdt( mem );  

                        if( ret==0 )  

                            printf( "Successfully detached memory /n" );  

                        else  

                            printf( "Memory detached failed %d/n",errno );  

                    }  

      &