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Internet Message Format | 1996-08-05 | 3.1 KB

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From: [e-mail] (John Noland)
Newsgroups: comp.os.msdos.programmer,comp.lang.c
Subject: Re: open vs fopen?
Date: 15 Feb 1996 00:31:27 GMT
Organization: Prose Software
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[e-mail] (Nathan T. Wild) writes:
>
>In C, why would one use open and DOS int handles rather than fopen and
>stdio file handles?
>
>The only reason I know of is UNIX portability.  Whenever I run across a
>unix program that uses the old-style open instead of fopen I usually
>end up rewriting it anyway though; I've had so many problems with
>the unix-style stuff I just rather would deal with the ANSI style.
>
>David
>>>Is there some speed advantage or differnet functionality?
>
>fopen() is mostly buffered, open() is, I believe, not. open() also gives some
>extra possible flags for sharing options. I use fopen() without problems.
>Besides, it's ANSI, and I program multiple programs and sometimes share
>modules that I'd have to check and redesign when switching from fopen to the
>local open command.

The open() function and its ilk are normally referred to as the "low-level"
I/O package. fopen() is the "Buffered" or "Standard" I/O package. The
strength of the low-level I/O functions is that they offer excellent control,
particularly when used with binary files. If you have a special I/O need, you
can use the low-level I/O routines to fashion the exact I/O package to fit
your needs.
The standard I/O package is one such creation. It is designed to provide fast
buffered I/O, mostly for text situations. For a lot of applications, using the
standard I/O package is simpler and more effective than using simple low-level
output. The essential feature is its use of automatic buffering. Buffered
I/O means reading and writing data in large chunks from a file to an array
and back. Reading and writing data in large chunks greatly speeds up the I/O
operations, while storing in an array allows access to the individual bytes.
The advantages of this approach should be apparent.
When fopen() is used, several things happen. The file, of course, is opened.
Second, an external character array is created to act as a buffer. The
<stdio.h> file has this buffer set to a size of 512 bytes. Third, a structure
is created to contain information about the buffer and the file. When you
call one of the functions from the standard I/O library, such as getc(),
the buffer is filled with data from the file. When getc() reaches the end of
the buffer, the buffer is automatically with the next block of data from the
file. You need not even be aware of the buffer, and you can program as if the
I/O functions worked directly with the file.
Technically, in DOS, all I/O is buffered since DOS itseld uses buffers
for disk I/O. This is a transparent function of the operating system and
has nothing to do with I/O packages included with C.

Hope this clarifies things.

-John Noland