open, close, dup, dup2, lseek, read, write, fileno, etc.

[Walter Bright]

Janice Caron wrote:
> On 09/02/2008, Walter Bright <newshound1 at digitalmars.com> wrote:
>> Going directly to the underlying OS functions makes for faster, more
>> efficient I/O. Calling open, close, etc., on Windows makes for poor
>> performance, because those functions are layered on top of the Windows
>> I/O functions.
> 
> Thanks for the answer. Though my question wasn't "Why does
> std.stream.File use them?", it was "Why can't I use them?", which is a
> slightly different question, and I see no reason for prohibition.

You can use them - they are in the C runtime library for Windows. Just 
put in the declarations for them. You'll be disappointed, though. They 
are NOT part of Windows, they are C runtime functions which mostly 
emulate the linux ones.

You're better off skipping the middleman.

> It is simpler easier to write platform-independent code if you can use
> open() and close(), because then you don't have to do
> 
>     version(Windows) { h = wide ? CreateFileW() : CreateFileA(); }
>     version(linux) { h = open(); }
> 
> Platform independent code is also inherently easier to test, if you
> don't happen to have a linux platform handy.

To write platform independent code, why not use the D I/O facilities? 
That is the point of them. If they are deficient, it is better to 
enhance them than use open/close/read/write/dup.

open/close/etc. are NOT platform independence. They are low level unix 
api functions. For example, for open() on windows, you have to go 
through one layer to CreateFileA() (and a lot of messing about trying to 
convert unix-style modes and permissions to windows-style), and internal 
to Windows, CreateFileA() executes a conversion to go to CreateFileW().

> I wasn't complaining though - it is trivially easy to import those
> functions with extern(C) so it's hardly a big deal. I was just
> curious.

I advise against using them because they are the wrong abstraction to 
use. For example, they are a direct reflection of the linux filesystem, 
not the Windows filesystem.