I have 2 programs (write.c and read.c). I want to continuously write to the named pipe from standard input, and read from it on the other end (and write to standard output). I've made something work, but it isn't working right. The program on the other end reads in the wrong order or reads special characters (so it reads more then it needs?). I also want to be able to compare the named pipe output to a certain string.
Anyways, here's the code from both files:
write.c:
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#define BUFFSIZE 512
#define err(mess) { fprintf(stderr,"Error: %s.", mess); exit(1); }
void main()
{
int fd, n;
char buf[BUFFSIZE];
mkfifo("fifo_x", 0666);
if ( (fd = open("fifo_x", O_WRONLY)) < 0)
err("open")
while( (n = read(STDIN_FILENO, buf, BUFFSIZE) ) > 0) {
if ( write(fd, buf, strlen(buf)) != strlen(buf)) {
err("write");
}
}
close(fd);
}
read.c:
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFFSIZE 512
#define err(mess) { fprintf(stderr,"Error: %s.", mess); exit(1); }
void main()
{
int fd, n;
char buf[BUFFSIZE];
if ( (fd = open("fifo_x", O_RDONLY)) < 0)
err("open")
while( (n = read(fd, buf, BUFFSIZE) ) > 0) {
if ( write(STDOUT_FILENO, buf, n) != n) {
exit(1);
}
}
close(fd);
}
Example of input:
hello how are you
123
test
Example of incorrect output:
hello how are you
b123
o how are you
btest
how are you
b
Another example of input:
test
hi
And output:
test
hi
t
Processes can use the open() function to access named pipes and then use the regular I/O functions for files, such as read() , write() , and close() , when manipulating named pipes. Buffered I/O functions can also be used to access and manipulate named pipes.
A named pipe is a one-way or duplex pipe that provides communication between the pipe server and some pipe clients. A pipe is a section of memory that is used for interprocess communication. A named pipe can be described as first in, first out (FIFO); the inputs that enter first will be output first.
FIFO is an abbreviation for first in, first out. It is a method for handling data structures where the first element is processed first and the newest element is processed last.
The buffer modify by read is not a valid c string so
write(fd, buf, strlen(buf)) != strlen(buf) // write.c
is undefined behaviour. You should do
write(fd, buf, n) != n
because you read n octet with read()
.
It's funny because you do it for read.c but not for write.c
The type of n
must but ssize_t
and not int
, man read.
main()
must return a int
Declare main prototype
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