NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part1/7079

Internet Message Format | 1996-08-05 | 1.8 KB

Path: lrz-muenchen.de!news
From: [e-mail] (Kurt Watzka)
Newsgroups: comp.lang.c
Subject: Re: fwrite help?
Date: 18 Feb 1996 11:45:37 GMT
Organization: Leibniz-Rechenzentrum, Muenchen (Germany)
Distribution: world
Message-ID: <4g73h1$[e-mail]>
References: <4fmaig$[e-mail]> <[e-mail]>
NNTP-Posting-Host: sun2.lrz-muenchen.de

[e-mail] (Derek Harmon) writes:

>[e-mail] writes:
>>What would the syntax for fwrite be to output 8 characters of
>>char line[10] to a file?  K&R doesn't write much about it. Thanks
>>for the help.

>size_t fwrite(const void *ptr, size_t size, size_t n, FILE *stream); is the
>prototype I have.  You can use line to devolve into a pointer towards the
>first element in line, sizeof(char) for size insures compatibility on machines
>where a character is more than one byte, and since you want 8 characters, set
>n to 8.

If sizeof(char) != 1, it's not C, it's somethig different. sizeof(char)
is 1 by definition. sizeof returns the size of it's operand in chars,
so, as far as the C programming language is concerned, there is _no_
chance for sizeof(char) to be anything but 1.

>: fwrite( line, sizeof(char), 8, fp);

>   Of course, when they are contiguous in an array, and you know the sizeof a
>char is 1 byte, it's much more efficient to say you want to write an 8-byte
>block of memory once, instead of a 1-byte block of memory eight times.

Nothing prevents the implementation of fwrite() to treat

  fwrite(line, 1, 8, fp)

as efficient as

  fwrite(line, 8, 1, fp)

The only neccessary difference is the value returned on successful
completion of the operation.

Kurt
--
| Kurt Watzka                             Phone : [phone]
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