使用系统调用pipe( )建立一个管道，然后使用系统调用fork( )创建2个子进程p1和p2。这2个子进程分别向管道中写入字符串：“Child process p1 is sending message！”和“Child process p2 is sending message！”，而父进程则从管道中读出来自两个子进程的信息，并显示在屏幕上。程序流程图

很高兴回答您的问题。下面是这个程序的流程图：

+------------------+
|     Main Process  |
+------------------+
          |
          | (1) create pipe
          |
+---------v----------+
|                    |
|    +-----------+   |
|    | Child p1  |   |
|    +-----------+   |
|          | (2) write to pipe
|          |
|    +-----------+   |
|    | Child p2  |   |
|    +-----------+   |
|          | (3) write to pipe
|          |
|    +-----------+   |
|    |   Parent  |   |
|    +-----------+   |
|          | (4) read from pipe
|          |
|    +-----------+   |
|    |   Display |   |
|    +-----------+   |
|                    |
+--------------------+

具体实现细节如下：

1. 在主进程中使用 `pipe()` 系统调用创建一个管道。
2. 父进程使用 `fork()` 创建子进程 p1。
3. 子进程 p1 向管道中写入字符串：“Child process p1 is sending message！”。
4. 父进程使用 `fork()` 创建子进程 p2。
5. 子进程 p2 向管道中写入字符串：“Child process p2 is sending message！”。
6. 父进程从管道中读取来自子进程 p1 的信息。
7. 父进程从管道中读取来自子进程 p2 的信息。
8. 父进程将读取到的信息显示在屏幕上。

具体代码实现可以参考下面的示例：

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

#define BUFFER_SIZE 256

int main() {
    int fd[2];
    char buffer[BUFFER_SIZE];
    pid_t pid1, pid2;

    /* Create a pipe */
    if (pipe(fd) == -1) {
        perror("pipe");
        exit(EXIT_FAILURE);
    }

    /* Fork the first child process */
    pid1 = fork();
    if (pid1 == -1) {
        perror("fork");
        exit(EXIT_FAILURE);
    } else if (pid1 == 0) {
        /* This is the first child process */

        /* Close the read end of the pipe */
        close(fd[0]);

        /* Write to the pipe */
        char *message = "Child process p1 is sending message!";
        write(fd[1], message, strlen(message));

        /* Close the write end of the pipe */
        close(fd[1]);

        /* Exit */
        exit(EXIT_SUCCESS);
    }

    /* Fork the second child process */
    pid2 = fork();
    if (pid2 == -1) {
        perror("fork");
        exit(EXIT_FAILURE);
    } else if (pid2 == 0) {
        /* This is the second child process */

        /* Close the read end of the pipe */
        close(fd[0]);

        /* Write to the pipe */
        char *message = "Child process p2 is sending message!";
        write(fd[1], message, strlen(message));

        /* Close the write end of the pipe */
        close(fd[1]);

        /* Exit */
        exit(EXIT_SUCCESS);
    }

    /* This is the parent process */

    /* Close the write end of the pipe */
    close(fd[1]);

    /* Read from the pipe */
    int bytes_read = read(fd[0], buffer, BUFFER_SIZE);

    /* Null-terminate the buffer */
    buffer[bytes_read] = '\0';

    /* Display the message */
    printf("Received from child p1: %s\n", buffer);

    /* Read from the pipe */
    bytes_read = read(fd[0], buffer, BUFFER_SIZE);

    /* Null-terminate the buffer */
    buffer[bytes_read] = '\0';

    /* Display the message */
    printf("Received from child p2: %s\n", buffer);

    /* Close the read end of the pipe */
    close(fd[0]);

    /* Wait for the children to exit */
    waitpid(pid1, NULL, 0);
    waitpid(pid2, NULL, 0);

    /* Exit */
    exit(EXIT_SUCCESS);
}