NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/6991

Text File | 1996-08-05 | 4.7 KB | 117 lines

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From: [e-mail] (John Noland)
Newsgroups: comp.os.msdos.programmer,comp.lang.c
Subject: Re: open vs fopen?
Date: 17 Feb 1996 01:01:24 GMT
Organization: Prose Software
Message-ID: <4g39d4$[e-mail]>
References: <[e-mail]> <4f8bev$[e-mail]> <[e-mail]> <4ftusv$[e-mail]> <danpop.824430285@rscernix>
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In article <danpop.824430285@rscernix>, [e-mail] says...
>
>In <4ftusv$[e-mail]> [e-mail] (John Noland) writes:
>
>>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.
>
>???  What can read/write do on a binary file that fread/fwrite cannot do?

Where in the above did I compare them with each other?

>
>>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.
>
>Same question as above.

Same question from me again. Are the read/write functions written using fread/
fwrite or is it vice versa? I believe, and feel free to correct me if I'm
wrong, that the fread/fwrite functions are written using the read/write
functions.

>
>>The standard I/O package is one such creation. It is designed to provide fast
>>buffered I/O, mostly for text situations.
>               ^^^^^^^^^^^^^^^^^^^^^^^^^^
>???

I use the stdio routines almost exclusively myself. Even for binary files.
That doesn't make the above statement wrong. Your statements seem to imply
that all systems are buffered at the OS level, so who cares what I/O
approach you use. You're not going to see any difference in I/O speed no
matter what. While this may be true for your particular situation, it's by
no means universal. The usefulness of buffering is in working sequentially
with a file. This makes buffered I/O well suited for text files. That
doesn't mean you can't or won't read a binary file sequentially or that it
sucks for use with binary files. Which, judging from what you've written,
is exactly what you'll think I meant.

>>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.
>
>Except that you can read and write data in large chunks using stdio
>routines.  The impact of the extra level of buffering is insignificant.

Isn't the above blurb talking about the stdio routines? Once again, your
reference to an extra level of buffering is not applicable to all systems.
If you're really referring to the low-level routines, then your statement
is not always true.

>
>>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.
>
>To a default size of _minimum_ 256 bytes.  I'm typing this text on a
>system which uses a default buffer size of 8192 bytes.  The size of the
>buffer can be controlled by the programmer via the setvbuf function.
>

That's a big default buffer. How many disk accesses does it take to fill
that thing? I seriously doubt you would want a buffer that big when reading
a file randomly. But, maybe your system is so fast you can afford that kind
of waste. In my <stdio.h> file, the constant BUFSIZ is 512. You say that
you can control the size of the buffer using setvbuf(). That's true, but it
doesn't change the default buffer size as you seem to imply. If I do the
following:

FILE *input, *output;

input = fopen("myfile.in", "r+b");
setvbuf(input, NULL, _IOFBF, 1024);

output = fopen("myfile.out", "w+b");

do you think output points to a buffer of the size set by setvbuf?  I don't
think this is what you meant.


>>Technically, in DOS, all I/O is buffered since DOS itself uses buffers
>>for disk I/O.
>
>The same applies to other operating systems (e.g. Unix) except that they
>do a much better job at buffering I/O than MSDOS.

Some versions of UNIX don't do any buffering at all.

>
>>Hope this clarifies things.
>
>So many inaccurate statements don't clarify things.  On the contrary.

The shit you have to up with when trying to be helpful.

John