Thread: helping a m8 fifo/pipes

hi my friend gave me some code and when comiling i get errors. The code contains fifo and i dont really have any idea about fifo and well i cant find any good tutorials/reading material about fifo i dont suppose anyone could tell me what i need to add to get this code working or link me to some stuff so i can learn fifo.

Code:

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


int myfork();

int main(void)
{
myfork();
}


int myfork(void)
{
int random, pipePrioity[2], pipePID[2];
pid_t pid;

printf("Child Process Being Created...please wait...\n");

sleep(2);																	                                                                    
pid = fork();																

if (pid == 0)
{


	printf("\nChild Prioity = %d", random);								
	printf("\nChild PID = %d\n\n", getpid());							
	char printTemp[10];													
	sprintf(printTemp, "%i", random);									
																				
	write(pipePrioity[1], printTemp, 5);								
	sprintf(printTemp, "%i", getpid());									
	write(pipePID[1], printTemp, 5);									
}
else if (pid > 0)
{
	int myfifoNum;
	int fifoint2;
	char fifochar1[80];

	sprintf( fifochar1, "%d|%d", random, getpid() );	

	fifoint2 = open(FIFO_NAME, O_WRONLY);

	if ((myfifoNum = write(fifoint2, fifochar1, strlen(fifochar1))) == -1)	
	{
		perror("write");
		printf("\nERROR WRITING TO PIPE\n");
	}
	else					
	{
		printf("\nPrint Job Sent to the Killer (DeSpooler)."); 
	}

	close(FIFO_NAME);
}
else
{
	perror("myfork");												
	printf("Error Creating Print Job.  Print Job Not Created");
	exit(1);																																			
}

output:

Code:

C:\Users\TraV\Desktop\c programming\meow2.c||In function `int myfork()':|
C:\Users\TraV\Desktop\c programming\meow2.c|46|error: `FIFO_NAME' was not declared in this scope|
C:\Users\TraV\Desktop\c programming\meow2.c|46|error: `O_WRONLY' was not declared in this scope|
||=== Build finished: 6 errors, 0 warnings ===|

i understand that i need to define a fifo name and stuff but i dont know how

I'm not accustomed to seeing C:\Users and <unistd.h> in the same place. Did you get other errors about missing header files? unistd.h is the "standard Unix" header, or some such name, and I wouldn't expect you to have it on a Win32 system (I don't think mingw includes it, but I can't check that right now).

I'm guessing you'd have more luck if you were on a linux system.

Originally Posted by tabstop

I'm not accustomed to seeing C:\Users and <unistd.h> in the same place. Did you get other errors about missing header files? unistd.h is the "standard Unix" header, or some such name, and I wouldn't expect you to have it on a Win32 system (I don't think mingw includes it, but I can't check that right now).

I'm guessing you'd have more luck if you were on a linux system.

well i have compiled it in ubuntu using cc
and this is the output

Code:

trav@travUBUNTU:~/Desktop$ cc lol.c -o lol
lol.c: In function ‘myfork’:
lol.c:46: error: ‘FIFO_NAME’ undeclared (first use in this function)
lol.c:46: error: (Each undeclared identifier is reported only once
lol.c:46: error: for each function it appears in.)
lol.c:46: error: ‘O_WRONLY’ undeclared (first use in this function)
lol.c:48: warning: incompatible implicit declaration of built-in function ‘strlen’
lol.c:65: error: expected declaration or statement at end of input

still same errors i think some of the code is missing and im trying to learn fifo and getting no where

strlen is in <string.h>. I believe O_WRONLY is in <fcntl.h>. I'm not sure where FIFO_NAME is; I've not seen any indication that it exists. The first argument of open is supposed to be a char* to a path; a cursory reading of the manual suggests that you'll want to use mkfifo to create such a thing.

Originally Posted by tabstop

strlen is in <string.h>. I believe O_WRONLY is in <fcntl.h>. I'm not sure where FIFO_NAME is; I've not seen any indication that it exists. The first argument of open is supposed to be a char* to a path; a cursory reading of the manual suggests that you'll want to use mkfifo to create such a thing.

thanks added in those header files made some errors go away
im getting there just had a read and mess about with fifo and i have managed to get my m8s program to compile and run using this code:

Code:

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

#define FIFO_NAME "my_fifo"


int myfork();

int main(void)
{
myfork();
}


int myfork(void)
{
int random, pipePrioity[2], pipePID[2];
pid_t pid;


int myfifoNum;
	int fifoint2;
	char fifochar1[80];
	  if (access(FIFO_NAME, F_OK) == -1)
		 {                     /* check if fifo already exists*/
     		   fifoint2 = mkfifo(FIFO_NAME, 0777);                /* if not then, create the fifo*/
     			if (fifoint2 != 0) 
			{
        		fprintf(stderr, "Could not create fifo %s\n", FIFO_NAME);
       			exit(EXIT_FAILURE);
    			 }
  		 }



random = rand()%10;
printf("Child Process Being Created...please wait...\n");

sleep(2);																	                                                                    
pid = fork();																

if (pid == 0)
{


	printf("\nChild Prioity = %d", random);								
	printf("\nChild PID = %d\n\n", getpid());							
	char printTemp[10];													
	sprintf(printTemp, "%i", random);									
																				
	write(pipePrioity[1], printTemp, 5);								
	sprintf(printTemp, "%i", getpid());									
	write(pipePID[1], printTemp, 5);									
}
else if (pid > 0)
{
	


	sprintf( fifochar1, "%d|%d", random, getpid() );	

	fifoint2 = open(FIFO_NAME, O_WRONLY);

	if ((myfifoNum = write(fifoint2, fifochar1, strlen(fifochar1))) == -1)	
	{
		perror("write");
		printf("\nERROR WRITING TO PIPE\n");
	}
	else					
	{
		printf("\nPrint Job Sent to the Killer (DeSpooler)."); 
	}

	exit(EXIT_SUCCESS);
}
else
{
	perror("myfork");												
	printf("Error Creating Print Job.  Print Job Not Created");
	exit(1);																																			
}
}

and the output is :

./lol
Child Process Being Created...please wait...

Child Prioity = 3
Child PID = 7562

3��

after that the program hangs and nothing else it outputted
i think there is a problem with the fifo/pipe anyone got any ideas?

Originally Posted by MK27

You never read from the fifo. Why would there be any output?

ok sorry im not very experienced with C and im new to fifo and pipes ect ect if I wanted to read from my fifo how could i implement this?

thankyou

Originally Posted by MK27

This is what I came up with. Notice the use of "perror" throughout -- you should look this command up and learn to use it:

Code:

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

int main() {
	char buffer[1024];
	int fin, fout;
	pid_t pid;
	if (mkfifo("pipefile", S_IRUSR | S_IWUSR)!=0) perror("mkfifo");

	if ((pid=fork())<0) perror("fork");
	if (pid==0) {		/* the child writes */
		if ((fin=open("pipefile", O_WRONLY))<3) perror("child open");
		if (write(fin,"hello world\0",12)<0) perror ("child write");
		return 0;
	} else {		/* the parent reads */
		if ((fout=open("pipefile", O_RDONLY))<3) perror("parent open");
		if (read(fout,buffer,1024)<0) perror("parent read");
		printf("Message: \"%s\"\n",buffer);
	}
	
	return 0;
}

1) Make the fifo and set read/write permission for the owner.
2) Fork and open the fifo for writing by the child process (then write something into it).
3) Back in the parent process, open the fifo for reading, read, and print the mesage to the screen.
4) Stir carefully and allow to cool.

The reason I used <3 with read and write is that 0,1, and 2 are the standard file descriptors (in, out, and error).

wow thanks i shall have a look and try to understand this i have to like have another .c file which reads the other end of fifo then kills processes and stuff. Im goin off for the night

thankyou alot i will post back

x

Originally Posted by MK27

Make the "parent" and "child" separate programs (obviously you won't need fork() then).

well this is what i have to do for my program

First process
This process will be required to run to create a series of child processes that will represent each of the printer jobs. The PID number of each child is to be inserted / spooled within a priority queue.
The queue will be made available to the second process to allow de-spooling.
The process should be configurable using command line arguments.

Second Process
This process will be separate from the first and running within a separate console window and will simulate the de-spooling process.
The process should be configurable using command line arguments.
It should perform the following functions:

Find and delete a number of printer jobs by priority order.
Print a message to notify the user of the deletion.
Kill the corresponding process.

It will be necessary to develop a communication mechanism to transfer data between the two main processes.

It should be possible to configure the maximum number of jobs allowed within the whole system.

It should also be possible to configure the consumer and / or the producer to specify how many jobs they will de-spool or spool during each cycle.

im still trying to get the first process all good before i start on the second one .