#ifndef _SHMDATA_H_HEADER
#define _SHMDATA_H_HEADER

#define TEXT_SZ 2048

struct shared_use_st
{
    int written;//作为一个标志，非0：表示可读，0表示可写
    char text[TEXT_SZ];//记录写入和读取的文本
};

#endif

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/shm.h>
#include "shmdata.h"

int main()
{
    int running = 1;//程序是否继续运行的标志
    void *shm = NULL;//分配的共享内存的原始首地址
    struct shared_use_st *shared;//指向shm
    int shmid;//共享内存标识符
    //创建共享内存
    shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666|IPC_CREAT);
    if(shmid == -1)
    {
        fprintf(stderr, "shmget failed\n");
        exit(EXIT_FAILURE);
    }
    //将共享内存连接到当前进程的地址空间
    shm = shmat(shmid, 0, 0);
    if(shm == (void*)-1)
    {
        fprintf(stderr, "shmat failed\n");
        exit(EXIT_FAILURE);
    }
    printf("\nMemory attached at %X\n", (int)shm);
    //设置共享内存
    shared = (struct shared_use_st*)shm;
    shared->written = 0;
    while(running)//读取共享内存中的数据
    {
        //没有进程向共享内存定数据有数据可读取
        if(shared->written != 0)
        {
            printf("You wrote: %s", shared->text);
            sleep(rand() % 3);
            //读取完数据，设置written使共享内存段可写
            shared->written = 0;
            //输入了end，退出循环（程序）
            if(strncmp(shared->text, "end", 3) == 0)
                running = 0;
        }
        else//有其他进程在写数据，不能读取数据
            sleep(1);
    }
    //把共享内存从当前进程中分离
    if(shmdt(shm) == -1)
    {
        fprintf(stderr, "shmdt failed\n");
        exit(EXIT_FAILURE);
    }
    //删除共享内存
    if(shmctl(shmid, IPC_RMID, 0) == -1)
    {
        fprintf(stderr, "shmctl(IPC_RMID) failed\n");
        exit(EXIT_FAILURE);
    }
    exit(EXIT_SUCCESS);
}

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/shm.h>
#include "shmdata.h"

int main()
{
    int running = 1;
    void *shm = NULL;
    struct shared_use_st *shared = NULL;
    char buffer[BUFSIZ + 1];//用于保存输入的文本
    int shmid;
    //创建共享内存
    shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666|IPC_CREAT);
    if(shmid == -1)
    {
        fprintf(stderr, "shmget failed\n");
        exit(EXIT_FAILURE);
    }
    //将共享内存连接到当前进程的地址空间
    shm = shmat(shmid, (void*)0, 0);
    if(shm == (void*)-1)
    {
        fprintf(stderr, "shmat failed\n");
        exit(EXIT_FAILURE);
    }
    printf("Memory attached at %X\n", (int)shm);
    //设置共享内存
    shared = (struct shared_use_st*)shm;
    while(running)//向共享内存中写数据
    {
        //数据还没有被读取，则等待数据被读取,不能向共享内存中写入文本
        while(shared->written == 1)
        {
            sleep(1);
            printf("Waiting...\n");
        }
        //向共享内存中写入数据
        printf("Enter some text: ");
        fgets(buffer, BUFSIZ, stdin);
        strncpy(shared->text, buffer, TEXT_SZ);
        //写完数据，设置written使共享内存段可读
        shared->written = 1;
        //输入了end，退出循环（程序）
        if(strncmp(buffer, "end", 3) == 0)
            running = 0;
    }
    //把共享内存从当前进程中分离
    if(shmdt(shm) == -1)
    {
        fprintf(stderr, "shmdt failed\n");
        exit(EXIT_FAILURE);
    }
    sleep(2);
    exit(EXIT_SUCCESS);
}