NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/6181

Internet Message Format | 1996-08-05 | 2.8 KB

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From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.os.msdos.programmer,comp.lang.c
Subject: Re: open vs fopen?
Date: Thu, 22 Feb 96 23:28:36 GMT
Organization: none
Message-ID: <[e-mail]>
References: <[e-mail]> <4f8qbg$[e-mail]> <4gg5nk$[e-mail]>
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In article <4gg5nk$[e-mail]>
           [e-mail] "Andreas Karnetzki" writes:

>[e-mail] schrieb:
>> [e-mail] (Nathan T. Wild) wrote:
>
>> >In C, why would one use open and DOS int handles rather than fopen and
>> >stdio file handles?
>
>> >Is there some speed advantage or differnet functionality?
>
>
>> because files opened using open and DOS files handles can be read and
>> write at the same time, while stdio files can't.
>
>That's not correct, I think. You can open files for read/write with the
>the stdio routines, too. Just use the "w+", "r+" or "a+" open modes with
>fopen().
>
>        fopen( "New.dat", "w+" );
>
>opens a file starting with 0 bytes for writing but with the possibility
>to switch to read mode without the need of closing it.
>
>        fopen( "Old.dat", "r+" );
>
>opens an (existing) file starting with reading with the possibility to
>switch to writing without closing.
>
>        fopen( "Any.dat", "a+" );
>
>opens for appending and maybe reading afterwards.
>
>The only thing to assure for read/write switches is to use an
>fseek() call between read and write operations:
>
>        fp = fopen( "My.dat", "r+" );
>        fwrite( "Hello", 1, 5, fp );
>        fseek( fp, 0L, SEEK_SET );

You could have fflush(), rewind() or fsetpos() instead here.

>        fread( Message, 1, 5, fp );
>        fseek( fp, 0L, SEEK_CUR );

You could have rewind() or fsetpos() instead here.

>        fwrite( " and Goodby.", 1, 12, fp );
>        fclose( fp );

>The main difference between stdio calls and the "low-level" routines
>(not only under DOS but for Unix too) is the absence of buffering in
>the low-level functions.

The 'low-level' functions typically have buffering in the OS. However
stdio typically implements an extra level of buffering local to the
particular program.

>if you use fwrite(), for example, you can not be sure that the number of
>bytes you want to write are actually written to the output at that time.
>The "real" write operation will take place if the stdio buffer for that
>file is full.

A good implementation of fwrite could bypass the stdio buffering where the
block sizes were appropriate.

--
-----------------------------------------
Lawrence Kirby | [e-mail]
Wilts, England | [e-mail]
-----------------------------------------