Path: utzoo!utgpu!water!watmath!clyde!rutgers!ucla-cs!cit-vax!elroy!ames!pasteur!agate!violet.berkeley.edu!dean
From: dean@violet.berkeley.edu (Dean Pentcheff)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Turbo C bug (?)
Summary: This results from \r\n conversion
Message-ID: <7056@agate.BERKELEY.EDU>
Date: 19 Feb 88 06:55:39 GMT
References: <734@agora.UUCP>
Sender: usenet@agate.BERKELEY.EDU
Reply-To: dean@violet.berkeley.edu.UUCP (Dean Pentcheff)
Followup-To: comp.sys.ibm.pc
Organization: University of California, Berkeley   Department of Zoology
Lines: 37

In article <734@agora.UUCP> qintar@agora.UUCP (Jim Seymour) writes:
>In version 1.0 I noticed what seemed to be a bug in the read() function.
>The docs claim (and the standard dictates) that this function returns the
>actual byte count read in from the file...

Actually, the reference under read() claims that "... a positive integer
is returned indicating the number of bytes placed in the buffer;  if the
file was opened in text mode, read does not count carriage returns or
Ctrl-Z characters in the number of bytes read."

A little experimentation clarifies this somewhat ambiguous statement.
Read() (in text mode) will read the requested number of
bytes from the file, but _then_ perform \r and ^Z elimination, fill your
buffer with whatever remains, and return the final number of characters
that ended up in your buffer (_after_ \r and ^Z removal).

A suggested fix is to use the Turbo _read() function which operates
purely, without \r and ^Z manipulation.  Alternately, you could open the
file using the O_BINARY flag, and use the normal read().

One interesting "feature" connected with this is the ambiguous case of
reading a file (in text mode) which consists of only '\r' characters.
The result turns out to be rather ugly:  if you read a buffer's worth
of '\r's, Turbo can't return a 0 for the number of characters placed in
the buffer, since that is supposed to mean EOF.  So, read() returns a
1, and (usually!) leaves a '\r' as the first character in the buffer.
On the last read before EOF, though, it seems to leave garbage in that
character position.  Gag, ack, blech.

-Dean


-----------------
Dean Pentcheff	(dean@violet.berkeley.edu)
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"A university is a place where people pay high prices for goods which they then
proceed to leave on the counter when they go out of the store."  Loren Eiseley