<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<!--Converted with LaTeX2HTML 96.1-c (Feb 29, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds -->
<HTML>
<HEAD>
<TITLE>6.3.3 FIFO Operations</TITLE>
<META NAME="description" CONTENT="6.3.3 FIFO Operations">
<META NAME="keywords" CONTENT="lpg">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<LINK REL=STYLESHEET HREF="lpg.css">
</HEAD>
<BODY LANG="EN">
<A NAME="tex2html548" HREF="node19.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="/icons//next_motif.gif"></A> <A NAME="tex2html546" HREF="node15.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="/icons//up_motif.gif"></A> <A NAME="tex2html540" HREF="node17.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="/icons//previous_motif.gif"></A> <A NAME="tex2html550" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="/icons//contents_motif.gif"></A> <BR>
<B> Next:</B> <A NAME="tex2html549" HREF="node19.html">6.3.4 Blocking Actions on </A>
<B>Up:</B> <A NAME="tex2html547" HREF="node15.html">6.3 Named Pipes (FIFOs </A>
<B> Previous:</B> <A NAME="tex2html541" HREF="node17.html">6.3.2 Creating a FIFO</A>
<BR> <P>
<H2><A NAME="SECTION00733000000000000000">6.3.3 FIFO Operations</A></H2>
<P>
I/O operations on a FIFO are essentially the same as for normal pipes, with
once major exception. An ``open'' system call or library function should be
used to physically open up a channel to the pipe. With half-duplex pipes,
this is unnecessary, since the pipe resides in the kernel and not on a physical
filesystem. In our examples, we will treat the pipe as a stream, opening it
up with fopen(), and closing it with fclose().
<P>
Consider a simple server process:
<P>
<PRE>/*****************************************************************************
Excerpt from "Linux Programmer's Guide - Chapter 6"
(C)opyright 1994-1995, Scott Burkett
*****************************************************************************
MODULE: fifoserver.c
*****************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <unistd.h>
#include <linux/stat.h>
#define FIFO_FILE "MYFIFO"
int main(void)
{
FILE *fp;
char readbuf[80];
/* Create the FIFO if it does not exist */
umask(0);
mknod(FIFO_FILE, S_IFIFO|0666, 0);
while(1)
{
fp = fopen(FIFO_FILE, "r");
fgets(readbuf, 80, fp);
printf("Received string: %s\n", readbuf);
fclose(fp);
}
return(0);
}</PRE>
<P>
Since a FIFO blocks by default, run the server in the background after you
compile it:
<P>
<PRE> $ fifoserver&</PRE>
<P>
We will discuss a FIFO's blocking action in a moment. First, consider the
following simple client frontend to our server:
<P>
<PRE>/*****************************************************************************
Excerpt from "Linux Programmer's Guide - Chapter 6"
(C)opyright 1994-1995, Scott Burkett
*****************************************************************************
MODULE: fifoclient.c
*****************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#define FIFO_FILE "MYFIFO"
int main(int argc, char *argv[])
{
FILE *fp;
if ( argc != 2 ) {
printf("USAGE: fifoclient [string]\n");
exit(1);
}
if((fp = fopen(FIFO_FILE, "w")) == NULL) {
perror("fopen");
exit(1);
}
fputs(argv[1], fp);
fclose(fp);
return(0);
}</PRE>
<P>
<BR> <HR>
<P><ADDRESS>
<I>Converted on: <BR>
Fri Mar 29 14:43:04 EST 1996</I>
</ADDRESS>
</BODY>
</HTML>
