使用管道和叉子用 C 语言编写程序？

Question

我有一个任务，我必须解决这个问题...我是 C 的完全新手，我仍在努力学习 C。

问题来了

编写一个创建管道和子进程的程序。父母反复设置警报 15 秒。触发警报时，父级计算自启动以来经过的秒数和微秒数，并通过管道将这些发送给子级。在获得信息时，孩子将它们显示在屏幕上。整个持续2分钟。

我已经尝试过这个问题，但我有很多错误..

这是我的解决方案..

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


int main(void)
{
        int     fd[2], nbytes;
    int fd2[2];
        pid_t   childpid;
        char    readbuffer1[80];
    char    readbuffer2[80];

         clock_t start, stop;
         long count;
         double time_sec, time_milli;
    const char* time1, time2;

        pipe(fd);
    pipe(fd2);
        childpid = fork();



        if(childpid == -1)
        {
                perror("fork");
                exit(1);
        }

        if(childpid == 0)
        {
                /* Child process closes up input side of pipe */
                close(fd[1]);


        /* Read in a string from the pipe */
        read(fd[0], readbuffer1, sizeof(readbuffer1));
        read(fd2[0], readbuffer2, sizeof(readbuffer2));
                printf("Received string 1: %s", readbuffer1);
        printf("Received string 2: %s", readbuffer2);

        }
        else
        {
                start = clock();
                /* Parent process closes up output side of pipe */

                alarm(15);
                /* Send "string" through the output side of pipe */


                stop = clock();



                time_sec = (double)(stop-start)/CLOCKS_PER_SEC;
        time_milli = time_sec*1000;
        sprintf(&time1,"%f",time_sec);
        sprintf(&time2,"%f",time_milli);
        close(fd[0]);
        write(fd[1], time1, (strlen(time1)+1));
        write(fd2[1], time2, (strlen(time2)+1));

        }

        return(0);
}

如何让这个运行 2 分钟？我怎样才能重复运行警报 15 秒？请帮忙....

Answer 1

好的。我已将您的代码更正如下。您可以直接编译并运行它。它应该可以工作。

您的代码有几个问题：

1. 您应该在 sprintf 之前为 time1 和 time2 分配内存空间。

2. 您应该使用 time() 而不是 clock()。看： clock() function always returning 0

3. 使用 sleep() 代替 alarm()

希望对您有所帮助！

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


int main(void){


int     fd[2];
int     nbytes;
int     fd2[2];
pid_t   childpid;
char    readbuffer1[80];
char    readbuffer2[80];

time_t start, stop;
long count;
double time_sec, time_milli;
char* time1;
char* time2;

pipe(fd);
pipe(fd2);
childpid = fork();

    if(childpid == -1)
    {
            perror("fork");
            exit(1);
    }

    if(childpid == 0)
    {
            /* Child process closes up input side of pipe */
            close(fd[1]);

      /* Read in a string from the pipe */
      read(fd[0], readbuffer1, sizeof(readbuffer1));
      read(fd2[0], readbuffer2, sizeof(readbuffer2));

          printf("Received string 1: %s", readbuffer1);
      printf("Received string 2: %s", readbuffer2);
    }
    else
    {

        close(fd[0]);

        time(&start);

          sleep(15);

          time(&stop);

      time_sec = stop-start;
      time_milli = time_sec*1000;

      time1 = malloc(80);
      time2 = malloc(80);

      sprintf(time1,"%f",time_sec);
      sprintf(time2,"%f",time_milli);


      write(fd[1], time1, (strlen(time1)+1));

      write(fd2[1], time2, (strlen(time2)+1));

    }
}

Answer 2

首先，如果你运行你的代码，你会得到什么错误？

我在您的代码中看到的第一个问题是您正在创建两个管道，而不是问题中提到的一个！！！

这应该创建一个合适的管道，你可以在其中做你的事情

编辑：我刚刚在我的代码中添加了一个简单的一次性通信。您所要做的就是将所有内容包装在一个循环中，该循环运行 2 分钟并在正确的时间发送警报。

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

int main()
{
        int pipefd[2];
        int rt;
        pid_t child = 0;

        // An array with some values
        char charBuffer[10] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
        // A buffer we use to communicate over the pipe
        char outputBuffer[10];

        if( pipe(pipefd) == -1 ) // Create new pipe
        {
                fprintf(stderr, "Failed to create pipe\n");
                exit(1);
        }

        child = fork();        // Create new Child

        if( !child )
        {
                printf("child created\n");
                close(pipefd[1]); // Child is read only

                // Wait for your alarm here
                while( read(pipefd[0], (void*)&outputBuffer, 10) > 0 )
                {
                    printf("Child received something over the pipe\n");
                    // Write output direct to stdout
                    rt = write(STDOUT_FILENO, &outputBuffer, 10);
                    rt = write(STDOUT_FILENO, "\n", 1);
                }
        }
        else if( child == -1 )
        {
                fprintf(stderr, "Error on fork - no child\n");
                exit(2);
        }
        else if( child > 0 )
        {
                close(pipefd[0]); // Parent is write only

                // Write our values to the pipe
                rt = write(pipefd[1], &charBuffer, 10);

                printf("Parent finished writing\n");
                close(pipefd[1]); // Signal writing is finished
        }

        return 0;
}

Answer 3

您只需 sleep 15 秒，然后将其包装成一个循环

for (int i = 0; i < 8; ++i) {
    sleep(15);
    /* do something, talk to your child, ... */
}