Pipes are used to establish communication between no. of processes.
creating a pipe in c:
To create a simple pipe with C, we make use of the pipe() system call. It takes a single argument, which is an array of two integers, and if successful, the array will contain two new file descriptors to be used for the pipeline. After creating a pipe, the process typically spawns a new process (remember the child inherits open file descriptors).
SYSTEM CALL: pipe();
PROTOTYPE: int pipe( int fd[2] );
RETURNS: 0 on success
-1 on error: errno = EMFILE (no free descriptors)
EMFILE (system file table is full)
EFAULT (fd array is not valid)
NOTES: fd[0] is set up for reading, fd[1] is set up for writing
The first integer in the array (element 0) is set up and opened for reading, while the second integer (element 1) is set up and opened for writing. Visually speaking, the output of fd1 becomes the input for fd0. Once again, all data traveling through the pipe moves through the kernel.
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
main()
{
int fd[2];
pipe(fd);
.
.
}
Remember that an array name in C decays into a pointer to its first member. Above, fd is equivalent to &fd[0]. Once we have established the pipeline, we then fork our new child process:
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
main()
{
int fd[2];
pid_t childpid;
pipe(fd);
if((childpid = fork()) == -1)
{
perror("fork");
exit(1);
}
.
.
}
