进程间通信----共享内存

int shmget(key_t key, size_t size, int shmflg);  

#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);  
}