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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Even more problems with lcc-win
Date: Fri, 24 Mar 2017 13:48:20 -0700
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BartC <bc@freeuk.com> writes:
[...]
> stdio.h exists in /usr/include/. There is also a version in 
> /usr/include/x64_64-linux-gnu/bits/

It's /usr/include/x86_64-linux-gnu/bits/,
not  /usr/include/x64_64-linux-gnu/bits/

But that second one is just another file that happens to have the same
name.  On my system, it includes the following lines:

    #ifndef _STDIO_H
    # error "Never include <bits/stdio.h> directly; use <stdio.h> instead."
    #endif

It's an *internal* file, part of the implementation, not something that
any C programmer needs to care about.  It doesn't provide, for example,
a declaration of printf, just some low-level declarations that are used
by the real <stdio.h>.  Apparently the designers found it useful to use
parallel file names (that directory contains several other files whose
names match those of standard headers).

> So the OS is providing stdio.h, and gcc tells me that is the one it uses 
> (the bits directory isn't directly specified in the include search path).

Actually it's provided by the libc6-dev package, at least on my Ubuntu
system -- but I think that package is preinstalled, so you could say
it's provided by the OS.

[...]

> Anyway I'm not sure why this is relevant: does the definition of 
> printf() differ wildly across OSes?

(I'm sure you mean the *declaration* of printf.)  It doesn't vary a
whole lot, though some systems will probably have to make the "restrict"
optional somehow to allow for pre-C99 compilers.

But the definition of type FILE probably does vary a great deal.

[...]

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"