使用管道在C中的子进程和父进程之间的双向通信 [英] two way communication between child and parent processes in C using pipes

问题描述

我希望父进程和子进程使用管道在C linux中进行通信。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。

但是我在下面的代码中获取ch和ch1字符串的输出为null。

请帮助我这个。

I want parent and child processes to communicate in C linux using pipes. I have created two file descriptors. one for parent to child i.e. readpipe and other writepipe for viceversa.
But I am getting null as output for ch and ch1 strings in my code below.
Please help me in this.

#include <stdio.h>
#include<stdlib.h>
#include 
#include<unistd.h>
int main()
{
    pid_t pid;
    int r;
    char *ch=NULL;
    char *ch1=NULL;
    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[1]);
            read(readpipe[0],ch,sizeof(ch));
            printf("\nREAD = %s",ch);
            close(readpipe[0]);
            ch1="YES";
            write(writepipe[1],ch1,sizeof(ch1));
            close(writepipe[1]);
    }
    else
    { //PARENT PROCESS
            close(writepipe[0]);
            close(writepipe[1]);
            ch="HI!! YOU THERE";
            write(readpipe[1],ch,sizeof(ch));
            close(readpipe[1]);
            read(writepipe[1],ch1,sizeof(ch1));
            printf("\nACK RECEIVED %s",ch1);
            close(writepipe[1]);
    }
    return 0;
}

谢谢......：）

Thanks...:)

推荐答案

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include<wait.h>
int main(void)
{
        pid_t pid;
        int r;
        char buf[1024];
        char cp[50];
        char ans;
        int readpipe[2];
        int writepipe[2];
        long 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("\nSIZE OF CP IS %d",sizeof(cp));
        printf("\nSEND SOMETHING TO CHILD PROCESS\t");
        scanf("%[^\n]%*c",&ans);
        fflush(stdin);
        pid=fork();
        if(pid==-1)
        {
                printf("pid:main");
                exit(1);
        }
        while(ans=='y' || ans=='Y')
        {
                if(pid==0)
                { 
                //CHILD PROCESS
                         if(ans=='n')
                        {
                                //a=getpid();
                                //printf("\nPARENT PROCESS a=%ld",a);
                                kill(pid,SIGKILL);
                        }

                        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");
                        fflush(stdin);
                        fgets(cp, 50, stdin);
                        printf("\nData Written to Parent%s",cp);
                        if(/*!strncmp("Q",cp,1) || */write(writepipe[1],cp,strlen(cp)+1) < 0)
                        {
                            break;
                        }
                        //printf("\nSEND SOMETHING TO PARENT PROCESS\t");
                        //fflush(stdin);
                        //scanf(" %[^\n]%*c",&ans);

                }
                else
                {
                        close(readpipe[0]);
                        close(writepipe[1]);
                        printf("\n(Parent)Enter data\t");
                        fgets(cp, 50, stdin);
                        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);
                        printf("\nSEND SOMETHING TO CHILD PROCESS\t");
                        fflush(stdin);
                        scanf(" %[^\n]%*c",&ans);
                        if(ans=='n')
                        {
                                kill(pid,SIGKILL);
                        }
                }
//              printf("\nSEND SOMETHING TO CHILD PROCESS\t");
//              scanf("%[^\n]%*c",&ans);

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

我看到两个问题（可能还有更多）......





1.在CHILD PROCESS的一半代码中，你关闭writepipe [1]然后写入它。



2在PARENT PROCESS的一半代码中，你关闭了两个写管脚，但后来又关闭了writepipe [1]。

I see two problems (there may be more) ...


1. In the CHILD PROCESS half of the code, you close writepipe[1] and then write to it.

2. In the PARENT PROCESS half of the code, you close BOTH writepipe handles but later close writepipe[1] again.

#include< stdio.h>

#include< unistd.h>

#include< sys types.h =>

#include< stdlib.h>

#include< memory.h>



int main（）{

//父母对孩子
int parentToChild [2];



//儿童为父母

int childToParent [2];



//字符串数据

char message1 [] =从孩子到父母的按摩;

char message2 [] =从父母到孩子的消息\ n;

char readBuffer [120];

pipe（parentToChi ld）;

pipe（childToParent）;

int processId，bytes;



if（（processId = fork（））== -1）{

printf（创建子进程时出错）;

}



if（processId == 0）{

//这里的子进程

//从孩子发送消息给父母

close（childToParent [0]）;

写（childToParent [1]，message1，strlen（message1）+1）;



/来自父母的/ recive消息

close（parentToChild [1]）;

bytes = read（parentToChild [0]，readBuffer，sizeof（readBuffer））;

printf（％s，readBuffer）;



//退出（1）;

}



if（processId！= 0）{

//这里的父流程

//从父母发送消息

close（parentToChild [0]）;

write（parentToChild [ 1]，message2，strlen（message2）+1）;



//收到孩子的留言

close（childToParent [1]） ;

bytes = read（childToParent [0]，readBuffer，sizeof（readBuffer））;

printf（％s，readBuffer）;

//退出（1）;

}



返回0;

}

#include <stdio.h>
#include <unistd.h>
#include <sys types.h="">
#include <stdlib.h>
#include <memory.h>

int main() {
//for parent to child
int parentToChild[2];

//for child to parent
int childToParent[2];

//string data
char message1[] = "massage from child to parent\n";
char message2[] = "message from parent to child\n";
char readBuffer[120];
pipe(parentToChild);
pipe(childToParent);
int processId , bytes;

if((processId = fork())== -1){
printf("error while creating a child process");
}

if(processId == 0){
//child process here
//send message from child to parent
close(childToParent[0]);
write(childToParent[1] , message1 , strlen(message1)+1);

//recive message from parent
close(parentToChild[1]);
bytes = read(parentToChild[0] , readBuffer , sizeof(readBuffer));
printf("%s",readBuffer);

// exit(1);
}

if(processId !=0 ){
//parent process here
//send message from parent to child
close(parentToChild[0]);
write(parentToChild[1] , message2 , strlen(message2)+1);

//recieve message from child
close(childToParent[1]);
bytes = read(childToParent[0] , readBuffer , sizeof(readBuffer));
printf("%s", readBuffer);
// exit(1);
}

return 0;
}

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