How to properly close a pipe - c

Question

I have a piece of code I am trying to alter. The code is simply 2 pipes that communicate between two processes (parent and child process). I am trying to create a "clean termination" of the program so that whenever a 0 is sent from parent to the child the respective process shuts down their end of all pipes.
The code is something like:
int main
{
int pipe1[2], pipe2[2], value, request;
if(pipe(pipe1) < 0 || pipe(pipe2) < 0)
printf("Failed to create pipes.\n");
switch(fork())
{
case -1:
perror("Cannot create fork.\n");
break;
case 0:
close (pipe1[WRITE]);
close (pipe2[READ]);
close (0);
close (1);
for(;;) {
read(pipe1[READ], &value, sizeof value);
//If user enters 0.
if(value == 0)
{
printf("Terminating child process!\n");
close(pipe1[READ]);
//write a 0 back to the parent so that it can close its end.
write(pipe2[WRITE], 0, sizeof (int));
close(pipe2[WRITE]);
exit(0);
}
else
{
/*Enter function to do something on the number here*/
write(pipe2[WRITE], &result, sizeof result);
}
}
break;
default: /* PARENT PROCESS - PRODUCER */
close(pipe1[READ]);
close(pipe2[WRITE]);
for(;;) {
printf("Ange ett tal: ");
scanf("%d", &value);
if(write(pipe1[WRITE], &value, sizeof value) != sizeof value)
{
perror("Cannot write thru pipe.\n");
return 1;
}
//Clean shutdown if value == 0
if(value == 0)
{
close(pipe2[WRITE]);
read(pipe2[READ],&result,sizeof(result));
if(result == 0)
{
close(pipe2[READ]);
printf("Pipe2[Read] closed!\n");
wait(0);
}
}
else
{
read(pipe2[READ],&result,sizeof(result));
printf("Result: %d.\n",result);
}
}
break;
}
}
I have been at this for hours now and I do not understand why my code is acting all crazy. When I enter 1 it says "Pipe closed and if i enter 0 it tries to accept another input before giving an error Cannot create pipes!.
I think I am missing something very fundamental here. Any help on the subject is very much appreciated.

Answer 1

Note the key change!
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
enum { READ = 0, WRITE = 1 };
int main(void)
{
int pipe1[2], pipe2[2], value, result;
if (pipe(pipe1) < 0 || pipe(pipe2) < 0)
printf("Failed to create pipes.\n");
switch (fork())
{
case -1:
perror("Cannot create fork.\n");
break;
case 0:
close(pipe1[WRITE]);
close(pipe2[READ]);
while (read(pipe1[READ], &value, sizeof(value)) > 0)
{
// If user enters 0.
if (value == 0)
{
printf("Terminating child process!\n");
close(pipe1[READ]);
// write a 0 back to the parent so that it can close its end.
write(pipe2[WRITE], 0, sizeof(int));
close(pipe2[WRITE]);
exit(0);
}
else
{
result = value + 1;
write(pipe2[WRITE], &result, sizeof result);
}
}
break;
default: /* PARENT PROCESS - PRODUCER */
close(pipe1[READ]);
close(pipe2[WRITE]);
for ( ; ; )
{
printf("Ange ett tal: ");
if (scanf("%d", &value) != 1)
break;
if (write(pipe1[WRITE], &value, sizeof(value)) != sizeof(value))
{
perror("Cannot write thru pipe.\n");
return 1;
}
// Clean shutdown if value == 0
if (value == 0)
{
close(pipe1[WRITE]); // Key change!
if (read(pipe2[READ], &result, sizeof(result)) <= 0 || result == 0)
{
close(pipe2[READ]);
printf("Pipe2[Read] closed!\n");
wait(0);
break;
}
}
else
{
if (read(pipe2[READ], &result, sizeof(result)) <= 0)
break;
printf("Result: %d.\n", result);
if (result == 0)
{
printf("Read zero - exit\n");
close(pipe1[WRITE]);
close(pipe2[READ]);
break;
}
}
}
break;
}
return 0;
}