Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hp-ses!hpcc01!hpccc!culberts
From: culberts@hpccc.HP.COM (Bruce Culbertson)
Newsgroups: comp.os.minix
Subject: Re: fopen (r+,w+,a+)
Message-ID: <6910002@hpccc.HP.COM>
Date: 21 Jul 89 02:31:42 GMT
References: <18518@louie.udel.EDU>
Organization: Hewlett-Packard Co.
Lines: 82

I think there are some incompatibilities between the recently posted
buffered I/O library routines and the ones I have used on BSD and
System V Unix.  In my experience, buffered files are flushed

	1) when their buffers fill,
	2) when explicitly flushed with a call to fflush(),
	3) when the file is closed,
	4) when the process calls exit(), and
	5) if stdin is read, stdout is flushed.

Unfortunately, I cannot seem to find a description of this in my
Unix documentation.  Perhaps someone else will find the documentation
and comment.

The new routines differ in the following ways:

	A) Stdout is not flushed when stdin is read.
	B) Stdout is flushed on all (f)printf's to stdout.
	C) Stdout is flushed after all newlines are written to stdout.

Problem A breaks several applications which perform fine on various
Unix systems.  The problem is not apparent if prompts for interactive
input are written with (f)printf because of B.  However, if a prompt is
written with (f)putc or fwrite, it never appears.  B and C are merely
performance issues, but perhaps are worth considering since stdio
exists solely to improve performance.  After implementing 5, I had
no further trouble with the new routines.  Having the "+" options
in fopen is a nice improvement.

------------------------------------------------------------------
/*  17 Jun 89   r+,w+,a+  added    RAL */

#include <stdio.h>



fgetc(iop)
FILE *iop;
{
	int ch;

	if ( testflag(iop, (_EOF | _ERR )))
		return (EOF);

	if (iop == stdin && stdout->_count > 0)
		fflush (stdout);

	if ( !testflag(iop, READMODE) ) {
                if (!testflag(iop, RDWRMODE))
		        return (EOF);
                fflush(iop);
                iop->_count = 0;
                iop->_ptr = iop->_buf;
                iop->_flags &= ~WRITEMODE;
                iop->_flags |= READMODE;
        }

	if (iop->_count <= 0){

		if ( testflag(iop, UNBUFF) )
			iop->_count = read(iop->_fd,&ch,1);
		else
			iop->_count = read(iop->_fd,iop->_buf,BUFSIZ);

		if (iop->_count <= 0){
			if (iop->_count == 0)
				iop->_flags |= _EOF;
			else
				iop->_flags |= _ERR;

			return (EOF);
		}
		else
			iop->_ptr = iop->_buf;
	}

	iop->_count--;		/* account one char */
	if (testflag(iop,UNBUFF))
		return (ch & CMASK);
	else
		return (*iop->_ptr++ & CMASK);
}