带有FIFO的Fork（）

Question

I am having the toughest time with this assignment. So this assignment I have two children(two separate programs) and they have to write to the parent (main). The parent has to read both data from the kids and then print it out. I have to use named pipes. Well so my FIFO keeps giving me "USAGE: NAMEPIPECLIENT[String]" message and I don't know why. The message is on the client side by the way. Also if someone can point me in a good direction on how to use fork with multiply children on separate files that would be really appreciated. Thanks in advance!Using GNU C

My Reader

#include<unistd.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<sys/stat.h>
#include<linux/stat.h>
#define FIFO_FILE "MYFIFO"         //default is current directory
int main(void){
  FILE *fpoint;
  char readbuffer[80];
  int again = 1;
  mknod(FIFO_FILE, S_IFIFO | 0666, 0);
  while(again){
    fpoint = fopen(FIFO_FILE, "r");
    fgets(readbuffer, 80, fpoint);
    printf("recevived string: %s\n, readbuffer");
    fclose(fpoint);
    if(strcmp(readbuffer, "stop") == 0 ) again = 0;
    return(0);
  }//exit main
}

My Writer

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<sys/stat.h>
#include<linux/stat.h>
#define FIFO_FILE "MYFIFO"
int main(int argc, char *argv[]){
  FILE *fpoint;
  int again =1;
  char strIn[80] = "Use message from command line";
  if(argc !=2){
    printf("USAGE: NamedPipeClient[string]\n");
    exit(1);
  }
  strcpy(strIn, argv[1]);
  while(again == 1){
    if((fpoint = fopen (FIFO_FILE, "w")) == NULL){
      perror("fopen");
      exit(1);
    }
    fputs(strIn, fpoint);
    fclose(fpoint);
    printf("Enter message to send: ");
    scanf("%s", strIn);
    again = strcmp(strIn, "Stop");
  }

  if((fpoint = fopen(FIFO_FILE, "w")) == NULL){
    perror("fopen");
    exit(1);
  }

  fputs(strIn,fpoint);
  fclose(fpoint);
  return(0);
}

Answer 1

Here is an extensively corrected version of the writer process

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

#define FIFO_FILE "MYFIFO"

int main(int argc, char *argv[])
{
    if(argc !=2)
    {
        printf("USAGE: NamedPipeClient[string]\n");
        exit(1);
    }

    FILE *fpoint;
    if((fpoint = fopen (FIFO_FILE, "w")) == NULL)
    {
        perror("fopen");
        exit(1);
    }

    char strIn[80];
    strcpy(strIn, argv[1]);


    int again =1;
    while(again == 1)
    {
        fputs(strIn, fpoint);

        printf("Enter message to send: ");
        scanf("%79s", strIn);
        again = strcmp(strIn, "Stop");
    }

    fputs(strIn,fpoint);
    fclose(fpoint);
    return(0);
}

This is the main reason that only one string is read:

while(again)
{
    fpoint = fopen(FIFO_FILE, "r");
    fgets(readbuffer, 80, fpoint);
    printf("recevived string: %s\n, readbuffer");
    fclose(fpoint);
    if(strcmp(readbuffer, "stop") == 0 ) again = 0;
    return(0);
}

Note that the function returns after only one pass through the loop.

Suggest:

while(again)
{
    fpoint = fopen(FIFO_FILE, "r");
    fgets(readbuffer, 80, fpoint);
    printf("recevived string: %s\n, readbuffer");
    fclose(fpoint);
    if(strcmp(readbuffer, "stop") == 0 ) again = 0;
}

return 0;

Note: return is not a function, (similar to sizeof is not a function), so no parens needed.

Note: the continually opening and closing of the FIFO is not a good idea.

Suggest only open once in any one process.

Suggest only close once in any one process.

When calling fopen() , always check the returned value to assure the operation was successful.