[ProgSoc] I can't get smoke out of my pipe

["vlrajews@nospam.acs.itd.uts.edu.au" <vlrajews@nospam.acs.itd.uts.edu.au>]

Can anybody explain why the following simple program does not work:
#include <stdio.h>
#include <unistd.h>

void main(void)
{
   int p[2];
   FILE* a;
   FILE* b;
   char s[100];

   pipe(p);
   a=fdopen(p[0],"r");
   b=fdopen(p[1],"w");
   fprintf(b,"foo foo foo \n");
   fgets(s,99,a);
   printf("%s\n",s);
}

I think this should work, but with some experimentation, discovered that
pipes usually need their write-ends closed before the read end receives
anything (I think). Thus if close(p[1]); is placed after fprintf, then it
should not hang. However, having done this, s is empty. Further
experimenting led me to replace fprintf(..) with :
   write(p[1],"ZXCZXCZXCZXC", 10);
This time, lo and behold, it worked. Can someone explain why the original
program does not work?

Cheers,

\/|<

Victor Rajewski
vik@nospam.progsoc.uts.edu.au
http://www.progsoc.uts.edu.au

`Man will occasionally stumble over the truth, but most of the time he
will pick himself up and continue on'
           - Winston Churchill, British statesman and writer (1874-1965)


--
You are subscribed to the progsoc mailing list. To unsubscribe, send a
message containing "unsubscribe" to progsoc-request@nospam.progsoc.uts.edu.au.
If you are having trouble, ask owner-progsoc@nospam.progsoc.uts.edu.au for help.

This list is archived at <http://www.progsoc.uts.edu.au/lists/progsoc/>