NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/5429

Internet Message Format | 1996-08-05 | 2.5 KB

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From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.lang.c
Subject: Re: open vs fopen?
Date: Fri, 09 Feb 96 23:06:23 GMT
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In article <4f7v8u$[e-mail]> [e-mail] "Mark Klenk" writes:

>Nathan Wild asked:
>>
>>In C, why would one use open and DOS int handles rather than fopen and
>>stdio file handles?
>
>        open() and family are really UNIX-isms that DOS adopted.
>
>        To answer your question, though:
>
>         a)  file I/O through open/close/read/write/lseek is generally
>              unbuffered and therefore in some cases faster, especially
>              in random-access situations

That is debatable. Where open etc. can be a win is if you create your own
buffering which is optimised to the code's usage patterns. FILE buffering
isn't bad but it is generalised and may not be optimal for specific
cases.

In Unix open() gives you finer control over the file mode and options
not available on fopen. 'int handles' are also used for other system
provided functions such as record locking and dealing with special/device
files. They are probably not as useful in DOS.

>         b)  ANSI C only defines fopen/fclose/fread/fwrite/fseek, which
>              by default usually provide buffered, but more portable, I/O

Right so if these do the job they are generally the appropriate choice.
They are also generally easier to use since you don't have to worry about
buffering yourself and you get powerful functions like printf. The
bottom line is that since open() isn't part of the C language you can't
use it in 'portable' C code.

>         c)  for sequential access, the f*() functions can improve I/O
>              performance because they generally do read-ahead and
>              write-behind in order to match system block-sizes more
>              closely

No, they don't (at least not any of the ones I've come across). To do this
would require asynchronous file I/O. It is almost always the OS that performs
any read-ahead hence both fopen and open style reads get the benefit.

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