NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/std/c/582

Internet Message Format | 1996-08-06 | 3KB

Path: mail2news.demon.co.uk!genesis.demon.co.uk
From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.std.c
Subject: Re: sizeof(char) ~= sizeof(float)
Date: Sun, 17 Mar 96 00:59:21 GMT
Organization: none
Message-ID: <[e-mail]>
References: <[e-mail]> <4gr3d1$[e-mail]> <[e-mail]>
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In article <[e-mail]>
           [e-mail] "Tanmoy Bhattacharya" writes:

>In article <[e-mail]>
>[e-mail] (Stephen Baynes) writes:
>
>SB: Tanmoy Bhattacharya ([e-mail]) wrote:
>SB: : In article <4gr3d1$[e-mail]>
>SB: : [e-mail] (Norman Diamond) writes:
>SB: <snip - copying data by using chars of different sorts vs memcpy >
>SB: : This was a free-standing implementation, and memcpy may be absent. (In
>SB: : a hosted implementation, as all read/write is done as if through
>SB: : getc/putc which handles unsigned char values, and binary files written
>SB: : out must be read back unchanged, the situation is impossible).
>SB:
>SB: That read/write is done by getc/putc does not imply very much about copying
>SB: chars. I don't see any requirement that fwrite/fread use one putc/getc per
>SB: byte(ie char) of memory. Fwrite could use one per bit writing the
>values 'Y' or
>SB: 'N' if it wanted so long as fread will read it back again. My
>understanding
>SB: is that the use of getc/putc means you can write a file with
>fwrite, copy it
>SB: with getc/putc and read the copy with fread to get what you started with.
>
>I understood it to mean that I could take the same (void*) pointer to
>the data, and call putc repeatedly on the successive bytes of the
>data, and the resulting file is identical to doing an fwrite. I think
>the standard should clarify its meaning.

OK, I'm a little late in getting round to this! :-)

This is a property that fread/fwrite really must have if they are to be
of much use. Without it you can't use them for random access reading/writing
of record because you don't know how large those records are going to
end up being in the file, even using a binary stream.

This would also bring into question whether:

fwrite(str, 1, strlen(str), fp)

has the same effect (ignoring the return values) as:

fputs(str, fp)

for valid arguments.

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