linux 有P1，P2，P3三个进程，P1和P2负责从键盘接收字符串，均发送给P3，P3接收到字符串，根据发送方分别显示”P3 received *** from P1（或P2）" ；分别用管道通信，消息队列和共享存储三种通信方式实现。形成完整的可运行代码，不需要注释。

使用管道通信方式实现：

P1：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

int main()
{
    int fd[2];
    char buf[100];

    if(pipe(fd) == -1) {
        perror("pipe");
        exit(1);
    }

    while(1) {
        printf("Enter message for P3 (from P1):\n");
        scanf("%s", buf);
        write(fd[1], buf, strlen(buf)+1);
    }

    return 0;
}

P2：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

int main()
{
    int fd[2];
    char buf[100];

    if(pipe(fd) == -1) {
        perror("pipe");
        exit(1);
    }

    while(1) {
        printf("Enter message for P3 (from P2):\n");
        scanf("%s", buf);
        write(fd[1], buf, strlen(buf)+1);
    }

    return 0;
}

P3：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

int main()
{
    int fd1[2], fd2[2];
    char buf[100];

    if(pipe(fd1) == -1) {
        perror("pipe1");
        exit(1);
    }

    if(pipe(fd2) == -1) {
        perror("pipe2");
        exit(1);
    }

    while(1) {
        read(fd1[0], buf, sizeof(buf));
        printf("P3 received %s from P1\n", buf);

        read(fd2[0], buf, sizeof(buf));
        printf("P3 received %s from P2\n", buf);
    }

    return 0;
}

使用消息队列通信方式实现：

P1：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/msg.h>

struct msgbuf {
    long mtype;
    char mtext[100];
};

int main()
{
    key_t key;
    int msgid;
    struct msgbuf buf;

    key = ftok(".", 'a');
    msgid = msgget(key, IPC_CREAT|0666);

    while(1) {
        printf("Enter message for P3 (from P1):\n");
        scanf("%s", buf.mtext);
        buf.mtype = 1;
        msgsnd(msgid, &buf, strlen(buf.mtext)+1, 0);
    }

    return 0;
}

P2：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/msg.h>

struct msgbuf {
    long mtype;
    char mtext[100];
};

int main()
{
    key_t key;
    int msgid;
    struct msgbuf buf;

    key = ftok(".", 'a');
    msgid = msgget(key, IPC_CREAT|0666);

    while(1) {
        printf("Enter message for P3 (from P2):\n");
        scanf("%s", buf.mtext);
        buf.mtype = 2;
        msgsnd(msgid, &buf, strlen(buf.mtext)+1, 0);
    }

    return 0;
}

P3：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/msg.h>

struct msgbuf {
    long mtype;
    char mtext[100];
};

int main()
{
    key_t key;
    int msgid;
    struct msgbuf buf;

    key = ftok(".", 'a');
    msgid = msgget(key, IPC_CREAT|0666);

    while(1) {
        msgrcv(msgid, &buf, sizeof(buf), 1, 0);
        printf("P3 received %s from P1\n", buf.mtext);

        msgrcv(msgid, &buf, sizeof(buf), 2, 0);
        printf("P3 received %s from P2\n", buf.mtext);
    }

    return 0;
}

使用共享存储通信方式实现：

P1：

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

struct shared_use_st {
    int written;
    char text[100];
};

int main()
{
    int running = 1;
    void *shm = NULL;
    struct shared_use_st *shared;
    char buffer[BUFSIZ];
    int shmid;

    shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666|IPC_CREAT);

    if(shmid == -1) {
        fprintf(stderr, "shmget failed\n");
        exit(EXIT_FAILURE);
    }

    shm = shmat(shmid, (void *)0, 0);

    if(shm == (void *)-1) {
        fprintf(stderr, "shmat failed\n");
        exit(EXIT_FAILURE);
    }

    shared = (struct shared_use_st *)shm;
    shared->written = 0;

    while(running) {
        printf("Enter message for P3 (from P1):\n");
        scanf("%s", buffer);

        while(shared->written == 1) {
            sleep(1);
            printf("Waiting for P3 to read...\n");
        }

        strncpy(shared->text, buffer, 100);
        shared->written = 1;
    }

    if(shmdt(shm) == -1) {
        fprintf(stderr, "shmdt failed\n");
        exit(EXIT_FAILURE);
    }

    if(shmctl(shmid, IPC_RMID, 0) == -1) {
        fprintf(stderr, "shmctl(IPC_RMID) failed\n");
        exit(EXIT_FAILURE);
    }

    return 0;
}

P2：

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

struct shared_use_st {
    int written;
    char text[100];
};

int main()
{
    int running = 1;
    void *shm = NULL;
    struct shared_use_st *shared;
    char buffer[BUFSIZ];
    int shmid;

    shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666|IPC_CREAT);

    if(shmid == -1) {
        fprintf(stderr, "shmget failed\n");
        exit(EXIT_FAILURE);
    }

    shm = shmat(shmid, (void *)0, 0);

    if(shm == (void *)-1) {
        fprintf(stderr, "shmat failed\n");
        exit(EXIT_FAILURE);
    }

    shared = (struct shared_use_st *)shm;
    shared->written = 0;

    while(running) {
        printf("Enter message for P3 (from P2):\n");
        scanf("%s", buffer);

        while(shared->written == 1) {
            sleep(1);
            printf("Waiting for P3 to read...\n");
        }

        strncpy(shared->text, buffer, 100);
        shared->written = 1;
    }

    if(shmdt(shm) == -1) {
        fprintf(stderr, "shmdt failed\n");
        exit(EXIT_FAILURE);
    }

    if(shmctl(shmid, IPC_RMID, 0) == -1) {
        fprintf(stderr, "shmctl(IPC_RMID) failed\n");
        exit(EXIT_FAILURE);
    }

    return 0;
}

P3：

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

struct shared_use_st {
    int written;
    char text[100];
};

int main()
{
    int running = 1;
    void *shm = NULL;
    struct shared_use_st *shared;
    int shmid;

    shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666|IPC_CREAT);

    if(shmid == -1) {
        fprintf(stderr, "shmget failed\n");
        exit(EXIT_FAILURE);
    }

    shm = shmat(shmid, 0, 0);

    if(shm == (void *)-1) {
        fprintf(stderr, "shmat failed\n");
        exit(EXIT_FAILURE);
    }

    shared = (struct shared_use_st *)shm;

    while(running) {
        if(shared->written == 1) {
            printf("P3 received %s from P1\n", shared->text);
            shared->written = 0;
        }

        if(shared->written == 2) {
            printf("P3 received %s from P2\n", shared->text);
            shared->written = 0;
        }

        sleep(1);
    }

    if(shmdt(shm) == -1) {
        fprintf(stderr, "shmdt failed\n");
        exit(EXIT_FAILURE);
    }

    if(shmctl(shmid, IPC_RMID, 0) == -1) {
        fprintf(stderr, "shmctl(IPC_RMID) failed\n");
        exit(EXIT_FAILURE);
    }

    return 0;
}