Question

我希望父进程和子进程使用管道在C linux中进行通信。首先，我希望父传递一个字符串，然后让孩子确认它。我创建了两个文件描述符。一个用于父母对孩子，即readpipe和其他writepipe for viceversa。问题是它没有把我的数据作为输入。另外，我希望printf语句如“输入你的数据”一次打印，但是因为在fork之后，有两个进程，所以它们被显示两次。任何替代方案??

 //readpipe[0] = child read
 //readpipe[1]= parent write

 //writepipe[0]=parent read
 //writepipe[1]=child write

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

 int main(void)
 {
     pid_t pid;
     int r;
    /* Hope this is big enough. */
     char buf[1024];
     char cp[50];
     char ans;
     int readpipe[2];
     int writepipe[2];
     int a;
     int b;
     a=pipe(readpipe);
     b=pipe(writepipe);
     if (a == -1) { perror("pipe"); exit(EXIT_FAILURE); }
     if (b == -1) { perror("pipe"); exit(EXIT_FAILURE); }

     printf("\nSEND SOMETHING TO CHILD PROCESS\t");
     scanf(" %c",&ans);
     pid=fork();
     if(pid==-1)
     {
         printf("pid:main");
         exit(1);
     }

     while(ans=='y' || ans=='Y')
     {
        printf("\nEnter data\t"); //printed twice
        fgets(cp, 50, stdin);     //not taking data
        printf("\n%s",cp);        
        if(pid==0)
        { //CHILD PROCESS
            close(readpipe[1]);
            close(writepipe[0]);
            read(readpipe[0],buf,sizeof(buf));
            printf("\nSENT\n %s",buf);
            write(writepipe[1],cp,strlen(cp)+1);
        }
        else
        { //PARENT PROCESS
            close(readpipe[0]);
            close(writepipe[1]);
            write(readpipe[1],cp,strlen(cp)+1);
            read(writepipe[0],buf,sizeof(buf));
            printf("\nRECEIVED\n %s",buf);
        }
        printf("\nSEND SOMETHING TO CHILD PROCESS\t");
        scanf(" %c",&ans);
   }
  close(readpipe[1]);
  close(writepipe[0]);
  close(readpipe[0]);
  close(writepipe[1]);

 return 0;
}

谢谢:)

Answer 1

您的代码中存在一些问题：

1

close(writepipe[1]);

您不应该关闭稍后需要的文件描述符。

2

read(readpipe[0],ch,sizeof(ch));

ch为NULL，这意味着您没有为其指定任何空间。

3

ch1="YES";
write(writepipe[1],ch1,sizeof(ch1));

您应该使用strlen(ch)+1而不是sizeof(ch)来查找需要写入的字节数。

4

您的父进程代码存在类似问题。

以下是基于此问题中代码的固定版本：

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

int main(void)
{
    pid_t pid;
    int r;
    /* Hope this is big enough. */
    char buf[1024];
    char *cp;

    int readpipe[2];
    int writepipe[2];
    int a;
    int b;
    a=pipe(readpipe);
    b=pipe(writepipe);
    // check a and b

    pid=fork();
    // check pid

    if(pid==0)
    { //CHILD PROCESS
        close(readpipe[1]);
        close(writepipe[0]);
        read(readpipe[0],buf,sizeof(buf));
        printf("\nREAD = %s",buf);
        close(readpipe[0]);
        cp="YES\n";
        write(writepipe[1],cp,strlen(cp)+1);
        close(writepipe[1]);
    }
    else
    { //PARENT PROCESS
        close(readpipe[0]);
        close(writepipe[1]);
        cp="HI!! YOU THERE";
        write(readpipe[1],cp,strlen(cp)+1);
        close(readpipe[1]);
        read(writepipe[0],buf,sizeof(buf));
        printf("\nACK RECEIVED %s",buf);
        close(writepipe[0]);
    }
    return 0;
}

C linux中子进程和父进程之间的通信：父进程没有阻塞

1 个答案: