编写Linux平台下的C应用程序，完成任务：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

以下是使用管道通信方式的C应用程序实现：

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

#define MAX_BUF_SIZE 1024

int main() {
    int p1[2], p2[2], nbytes;
    char buf[MAX_BUF_SIZE];

    if (pipe(p1) == -1 || pipe(p2) == -1) {
        perror("pipe");
        return 1;
    }

    pid_t pid = fork();

    if (pid == -1) {
        perror("fork");
        return 1;
    }

    if (pid == 0) {
        // P3 process
        close(p1[1]);
        close(p2[1]);

        while (1) {
            if ((nbytes = read(p1[0], buf, MAX_BUF_SIZE)) > 0) {
                buf[nbytes] = '\0';
                printf("P3 received %s from P1\n", buf);
            }

            if ((nbytes = read(p2[0], buf, MAX_BUF_SIZE)) > 0) {
                buf[nbytes] = '\0';
                printf("P3 received %s from P2\n", buf);
            }
        }

        close(p1[0]);
        close(p2[0]);
    } else {
        pid_t pid2 = fork();

        if (pid2 == -1) {
            perror("fork");
            return 1;
        }

        if (pid2 == 0) {
            // P2 process
            close(p1[0]);
            close(p2[1]);

            while (1) {
                printf("P2 enter a string: ");
                fgets(buf, MAX_BUF_SIZE, stdin);
                write(p1[1], buf, strlen(buf));
            }

            close(p1[1]);
            close(p2[0]);
        } else {
            // P1 process
            close(p1[1]);
            close(p2[0]);

            while (1) {
                printf("P1 enter a string: ");
                fgets(buf, MAX_BUF_SIZE, stdin);
                write(p2[1], buf, strlen(buf));
            }

            close(p1[0]);
            close(p2[1]);
        }
    }

    return 0;
}

以下是使用消息队列通信方式的C应用程序实现：

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

#define MAX_MESSAGE_SIZE 1024

struct message {
    long mtype;
    char mtext[MAX_MESSAGE_SIZE];
};

int main() {
    int qid;
    key_t key;
    struct message msg;

    if ((key = ftok(".", 'a')) == -1) {
        perror("ftok");
        return 1;
    }

    if ((qid = msgget(key, IPC_CREAT | 0666)) == -1) {
        perror("msgget");
        return 1;
    }

    pid_t pid = fork();

    if (pid == -1) {
        perror("fork");
        return 1;
    }

    if (pid == 0) {
        // P3 process
        while (1) {
            if (msgrcv(qid, &msg, MAX_MESSAGE_SIZE, 1, 0) > 0) {
                printf("P3 received %s from P1\n", msg.mtext);
            }

            if (msgrcv(qid, &msg, MAX_MESSAGE_SIZE, 2, 0) > 0) {
                printf("P3 received %s from P2\n", msg.mtext);
            }
        }
    } else {
        pid_t pid2 = fork();

        if (pid2 == -1) {
            perror("fork");
            return 1;
        }

        if (pid2 == 0) {
            // P2 process
            while (1) {
                printf("P2 enter a string: ");
                fgets(msg.mtext, MAX_MESSAGE_SIZE, stdin);
                msg.mtype = 2;
                msgsnd(qid, &msg, strlen(msg.mtext) + 1, 0);
            }
        } else {
            // P1 process
            while (1) {
                printf("P1 enter a string: ");
                fgets(msg.mtext, MAX_MESSAGE_SIZE, stdin);
                msg.mtype = 1;
                msgsnd(qid, &msg, strlen(msg.mtext) + 1, 0);
            }
        }
    }

    msgctl(qid, IPC_RMID, NULL);

    return 0;
}

以下是使用共享存储通信方式的C应用程序实现：

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

#define MAX_BUF_SIZE 1024

int main() {
    int shmid1, shmid2;
    char *shm1, *shm2;

    if ((shmid1 = shmget(IPC_PRIVATE, MAX_BUF_SIZE, IPC_CREAT | 0666)) == -1 ||
        (shmid2 = shmget(IPC_PRIVATE, MAX_BUF_SIZE, IPC_CREAT | 0666)) == -1) {
        perror("shmget");
        return 1;
    }

    if ((shm1 = shmat(shmid1, NULL, 0)) == (char *) -1 ||
        (shm2 = shmat(shmid2, NULL, 0)) == (char *) -1) {
        perror("shmat");
        return 1;
    }

    pid_t pid = fork();

    if (pid == -1) {
        perror("fork");
        return 1;
    }

    if (pid == 0) {
        // P3 process
        while (1) {
            if (*shm1 != '\0') {
                printf("P3 received %s from P1\n", shm1);
                *shm1 = '\0';
            }

            if (*shm2 != '\0') {
                printf("P3 received %s from P2\n", shm2);
                *shm2 = '\0';
            }
        }
    } else {
        pid_t pid2 = fork();

        if (pid2 == -1) {
            perror("fork");
            return 1;
        }

        if (pid2 == 0) {
            // P2 process
            while (1) {
                printf("P2 enter a string: ");
                fgets(shm2, MAX_BUF_SIZE, stdin);
            }
        } else {
            // P1 process
            while (1) {
                printf("P1 enter a string: ");
                fgets(shm1, MAX_BUF_SIZE, stdin);
            }
        }
    }

    shmdt(shm1);
    shmdt(shm2);

    shmctl(shmid1, IPC_RMID, NULL);
    shmctl(shmid2, IPC_RMID, NULL);

    return 0;
}