Fork() with FIFO - c

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.