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Date: Sun, 17 Mar 2013 22:06:10 -0500
From: Rob Landley <rob@...dley.net>
To: musl@...ts.openwall.com
Cc: musl@...ts.openwall.com
Subject: Re: question: hard-coded file descriptors in
stdin/stdout/stderr
On 03/14/2013 11:18:53 AM, Zvi Gilboa wrote:
> Greetings,
>
> I just noticed that the file descriptors in stdin.c, stdout.c, and
> stderr.c do not use the #defines from <unistd.h> (namely
> STDIN_FILENO, STDOUT_FILENO, and STDERR_FILENO), but are rather
> hard-coded (as 0, 1, and 2 respectively).
Because these have been constant values since 1969, were adopted by DOS
in 1983, and the numerical values are SPECIFIED BY POSIX:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/stdin.html
STDIN_FILENO - Standard input value, stdin. Its value is 0.
STDOUT_FILENO - Standard output value, stdout. Its value is 1.
STDERR_FILENO - Standard error value, stderr. Its value is 2.
> I was therefore wondering whether there was a special reason for that?
Because MUSL is simple and using a macro to specify a constant that's
standardized by posix, has been stable for over 40 years, and is
regularly used on the command line, is pointless?
> With POSIX systems this would normally not be an issue, however there
> are still some
> systems out there with standard file descriptor numbers which are
> different...
Posix specifies the value of the constant. Supporting systems that
violate posix was not, last I checked, part of musl's goals?
> On that same note: wouldn't it make sense to slightly modify unistd.h
> so that it
> first checks whether STDIN_FILENO, etc. have already been defined?
> That would allow
> a system with different standard file descriptor numbers to define
> them in one of
> the /arch headers, yet enable the default for systems that use the
> "normal" numbers.
> The relevant section would then read:
What system are you referring to? "There are systems" means what,
exactly>
Not Linux, not Mac, not Android, not iOS... what are you referring to?
Rob
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