Xref: utzoo comp.sys.hp:4371 comp.lang.c:26086
Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!cernvax!chx400!forty2!mecazh!paul
From: paul@mecazh.UUCP (Paul Breslaw)
Newsgroups: comp.sys.hp,comp.lang.c
Subject: Unbuffered Stdio Input
Keywords: stdio, buffering, ptys
Message-ID: <378@node17.mecazh.UUCP>
Date: 19 Feb 90 22:29:29 GMT
Reply-To: paul@zurich01.UUCP (Paul Breslaw)
Organization: Mecasoft SA, CH-8057 Zurich, Switzerland
Lines: 42


I have a little program that opens a master side pty and reads from it.
I have another little program that opens the corresponding slave side
and writes to it.

If the master side is coded something like:-

    FILE *f;
    char buf[ BF ];
    int  nr;

    f = fopen( master, "a+" );
    nr = fread( buf, sizeof( char ), BF, f );

then the program hangs on the fread.

If, however, I replace the last line with

    nr = read( fileno( f ), buf, BF );

then the read succeeds. An optional 

    setbuf( f, NULL );

does not alter the situation.

I have tested the program on an HP9000/340 (HP-UX 6.5) and a 
Sun3/50 (SunOS 3.5) with not quite identical non-events :-)

Any suggestions what I've done wrong?


Paul Breslaw




-- 
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Paul Breslaw, Mecasoft SA,          |  telephone :  41 1 362 2040
Guggachstrasse 10, CH-8057 Zurich,  |  e-mail    :  mcsun!chx400!mecazh!paul
Switzerland.                        |               paul@mecazh.UUCP