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;
}

Answer 1

你打电话

    printf("\nEnter data\t"); //printed twice
    fgets(cp, 50, stdin);     //not taking data

在之前

，检查您是在父进程还是子进程中。这当然会导致两个进程都打印，并且两者都是标准输入。因此，不清楚哪个进程会读取您输入的日期。

这些问题会出现同样的问题：

printf("\nSEND SOMETHING TO CHILD PROCESS\t"); scanf(" %c",&ans);

我建议你重新设计你的程序，以清楚地分离在父进程fork()中运行的代码和在子进程中运行的代码。

Answer 2

为什么fgets不接受数据？在第一次扫描中，您正在读取单个字符，新行仍将在中输入缓冲区，这将跳过

要解决这个问题，你应该使用scanf（“％[^ \ n]％* c”，＆amp; ans） - 有关详细信息，请参阅this
找到修改过的代码..它可能会对你有所帮助（从我做出一些改变的时候打破，我验证了基本功能）

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("%[^\n]%*c",&ans);
//ans = getchar();
fflush(stdin);
pid=fork();
if(pid==-1)
{
    printf("pid:main");
    exit(1);
}

while(ans=='y' || ans=='Y')
{
    if(pid==0)
    { 
        //CHILD PROCESS
        close(readpipe[1]);
        close(writepipe[0]);
        if(read(readpipe[0],buf,sizeof(buf)) < 0)
        {
            break;
        }

        printf("\nChild Process Read: %s\n",buf);

        printf("\n(child)Enter data:\t"); //printed twice
        fgets(cp, 50, stdin);     //not taking data
        printf("\nData Written to Parent%s",cp);
        if(!strncmp("Q",cp,1) || write(writepipe[1],cp,strlen(cp)+1) < 0)
        {
            break;
        }
    }
    else
    { 
        //PARENT PROCESS
        close(readpipe[0]);
        close(writepipe[1]);
        printf("\n(Parent)Enter data\t"); //printed twice
        fgets(cp, 50, stdin);     //not taking data

        printf("\nData Writtent to Child: %s",cp);
        if(!strncmp("Q",cp,1) || write(readpipe[1],cp,strlen(cp)+1) < 0)
        {
            break;
        }        

        if(read(writepipe[0],buf,sizeof(buf)) < 0)
        {
            break;
        }
        printf("\nParent Process Read: %s\n",buf);
    }
    ans ='y';
}

close(readpipe[1]);
close(writepipe[0]);
close(readpipe[0]);
close(writepipe[1]);
return 0;

}

在C linux中使用管道的2路通信

2 个答案: