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From: Waldek Hebisch
Subject: anyfile and blockwrite
Date: 19 Nov 2009, 00:53:01

Wolfgang Helbig wrote:
> Hi,
> 
> Using blockwrite with Anyfile surprises me:
> 
> The type definitions are:
> byteFile= file of packed record b: eightbits end;
> eightbits = 0..255;
> 
> And the variables:
> dvibuf: array [0..800] of eightbits;
> dvifile: byteFile;
> 
> 
> The file is opened by rewrite(dvifile, filename) and then written by
> procedure writeit(f: anyfile);
> begin blockwrite(f, dvibuf[0..211], 212) end;
> 
> I expected to get a file with 212 bytes like this one:
> osx $ od -tu1 expected
> 0000000   247   2   1 131 146 192  28  59   0   0   0   0   3 232  27  32
> 
> But instead I get this file, the length is correct, but every byte occupies 32 bit, the higher bytes are not written at all.
> 
> osx $ od -tu1 unexpected
> 0000000   247   0   0   0   2   0   0   0   1   0   0   0 131   0   0   0
> 0000020   146   0   0   0 192   0   0   0  28   0   0   0  59   0   0   0
> 
> All this is done with gpc version 20070904 on Mac OS X 10.6.2.
> 
> I want to make minimal use of GPC extensions, thats why I didn't use the GPC byte for eight_bits or didn't use
> packed on subranges. I'd prefer to use packed file of eightbits instead, but GPC ignores packed for files.
> 
> And then I'd like to use buffered output without changing the source file!
> 

Declaration for 'dvifile' does not matter.  'blockwrite' simply writes
content of 'dvibuf', exactly how it is stored in memory.  AFAICS you
want:

dvibuf: packed array [0..800] of eightbits;

GPC simply stores each record in a separate machine word.  Compare
'SizeOf(dvibuf)' with both your original declaration and with
packed added.

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