使用管道的进程间通信 (IPC)

Question

Consider you have two variables for questions and answers as below char* questions[] = {"Quit", "In which university do you study?", "Which course are you studying?", "What is your area of interest?"};

char* answers[] = {"Quit", "DAIICT", "Systems Software", "Kernel Programming"};

• Parent process will accept input as question number from user. If the question number is between 0 to 3, the actual text of question will be sent from parent to child process using the following.

write(fd1[WRITE], questions[que], strlen(questions[que])+1);

• Once parent sends the question to child, it just waits for getting answer back from child using the following.

bytesRead = read(fd2[READ], message, MSGLEN);

• When child process receives the question using the following.

bytesRead = read(fd1[READ], message, MSGLEN );

• Child process then finds the index of the question that it receives from questions[] string array. It uses that index to get the correct answer from the answers[] string array.

• Child process then replies to the parent the answer using using the following.

write(fd2[WRITE], answers[que], strlen(answers[que])+1);

• If child finds that question number is equal to 0 (ie Quit) then it exits after closing all the open file handles. Parent process upon reading question number equal to 0 from and after receiving “Quit” as the answer from child closes all open file handles and waits for child to exit using wait() system call to ensure that we don't create a zombie child process. Once parent comes out of wait() system call, it also exits.

Answer 1

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

#define READ 0
#define WRITE 1

int main()
{
  int i,que,bytesRead;
  int fd1[2],fd2[2];
  char message[100];

  char* questions[] = {"Quit","In which university do you study?","Which course are you studying?","What is your area of interest?"};
  char* answers[] = {"Quit", "DAIICT", "Systems Software", "Kernel Programming"};

  pipe(fd1);
  pipe(fd2);

  if(fork() ==0)
  {
    close(fd1[WRITE]);
    close(fd2[READ]);

    while(1){
      bytesRead = read(fd1[READ], message,100 );
      for(i=0;i<4;i++)
      {
        if(strcmp(message,questions[i])==0)
        {`enter code here`
            break;

        }
      }

    write(fd2[WRITE], answers[i], strlen(answers[i])+1);
    if(i==0)
    {
      close(fd1[1]);
      close(fd2[0]);

      printf("Child exiting for you entered 0\n");
      exit(0);
    }
    }
  }


  else
  {

    close(fd1[READ]);
    close(fd2[WRITE]);
    while(1)
    {



      printf("Enter digit from 0 to 3\n");
      scanf("%d", &que);//dont show correct output if input is greater than 3
      printf("Your choice is  '%s'\n",questions[que]);

      write(fd1[WRITE], questions[que], strlen(questions[que])+1);
      bytesRead = read(fd2[READ], message, 100);

      if(strcmp(message,answers[0])==0)
      {
        close(fd1[WRITE]);
        close(fd2[READ]);

        wait(fork());
        printf("Parent exiting for you entered 0\n");
        exit(0);
      }
      printf("Answer is '%s' \n",message);
    }
    return 0;
}
}