linux C学习笔记02--共享内存(进程同步）

 system V下3中进程同步：共享内存(shared memory)，信号量(semaphore)和消息队列(message queue)

调试了下午，终于调通啦！ 运行./c.out 输出共享内存中的内容，运行 ./c.out arg1 对共享内存区进行修改,shell下输入ipcs -m 可以查看共享内存情况 ，-s 是信号量，-q 是消息队列

下面先贴上main的代码： 

#include <signal.h>        //head file of define signal
#include <pthread.h>
#include <static_lib.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/mman.h>extern int create_shm(char **shmptr);
int main(int argc,char* argv[])
{//IPC share memorychar *shmptr;if(create_shm(&shmptr) == -1){printf("create_shm error \n");return -1;        }if(argc > 1){//do the second thing for share memorywhile(1){printf("input str to share memory:");gets(shmptr);}}else{memcpy(shmptr,"hello",5);while(1){sleep(2);printf("share memory is %s \n",shmptr);}}   return 0;
}

下面是共享内存创建的代码：

/*************************************************************************> File Name: share_memory.c> Author: hailin.ma> Mail: mhl2018@126.com > Created Time: Wed 27 May 2015 11:19:26 PM CST************************************************************************/#include<stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/shm.h>
#include <sys/ipc.h>
#include <errno.h>#define SHARE_MEM_KEY 26int create_shm(char **shmptr)
{int shmid;//if((shmid = shmget(IPC_PRIVATE,200,IPC_CREAT|IPC_EXCL|0666)) == -1)if((shmid = shmget(SHARE_MEM_KEY,200,IPC_CREAT|IPC_EXCL|0666)) == -1){perror("shmget");if(errno == EEXIST){shmid = shmget(SHARE_MEM_KEY,0,0);if(shmid == -1){perror("shmget2");return -1;}else{if((*shmptr = shmat(shmid,0,0666)) == (void*)-1){perror("shmat2");return -1;}else{return shmid;}}}else{return -1;}}if((*shmptr = shmat(shmid,0,0)) == (void*)-1){perror("shmat");return -1;}return shmid;
}

 运行效果：

05.29日增加了共享内存释放和删除：

int main(int argc,char* argv[])
{//IPC share memorychar *shmptr;int shmid;if((shmid =create_shm(&shmptr)) == -1){printf("create_shm error \n");return -1;        }if(argc > 1){//do the second thing for share memorywhile(1){printf("input str to share memory:");gets(shmptr);if(shmptr[0] == 'q')        //quit{shmdt(shmptr);            //disconnect to the share memory but will not dellect the memerybreak;}}}else{while(1){sleep(2);printf("share memory is: %s \n",shmptr);if(shmptr[0] == 'q'){shmdt(shmptr);shmctl(shmid,IPC_RMID,NULL);        //delete the share memerybreak;}}}
}