Re: [fpc-pascal] Fixed record files
Thanks for the link. For best compatibility should I make it:
Type
DrawCMD = Packed Record
GC: Word;
PX,PY,PZ,GX,GY,GZ,GI,GJ,R,SA,EA:Double;
End;
Or
Type
{$PackRecords 2}
DrawCMD = Record
GC: Word;
PX,PY,PZ,GX,GY,GZ,GI,GJ,R,SA,EA:Double;
End;
{$PackRecords default}
Or am I not understanding this correctly?
James
From: fpc-pascal [mailto:fpc-pascal-boun...@lists.freepascal.org] On Behalf Of
Vojtech Cihák
Sent: Sunday, July 09, 2017 2:44 PM
To: FPC-Pascal users discussions <fpc-pascal@lists.freepascal.org>
Subject: Re: [fpc-pascal] Fixed record files
Hi,
"packed record" is for compatibility. Its guaranteed that inner alignment and
size of record will be always the same and will not change in future versions
of compiler, unlike the plain "record".
https://www.freepascal.org/docs-html/ref/refsu15.html
V.
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Re: [fpc-pascal] Fixed record files
Hi, "packed record" is for compatibility. Its guaranteed that inner alignment and size of record will be always the same and will not change in future versions of compiler, unlike the plain "record". https://www.freepascal.org/docs-html/ref/refsu15.html V. __ Od: "James Richters" <ja...@productionautomation.net> Komu: "'FPC-Pascal users discussions'" <fpc-pascal@lists.freepascal.org> Datum: 09.07.2017 20:12 Předmět: Re: [fpc-pascal] Fixed record files I don't understand "packed record" could you elaborate? James ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal <http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal> ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] Fixed record files
I prefer performance over size, The only reason 'GC' was a byte was because it
didn't really need to be a word, however it wouldn't hut to be a word anyway,
so I could just use this:
Type
DrawCMD = Record
GC: Word;
PX,PY,PZ,GX,GY,GZ,GI,GJ,R,SA,EA:Double;
End;
I don't understand "packed record" could you elaborate?
James
-Original Message-
From: fpc-pascal [mailto:fpc-pascal-boun...@lists.freepascal.org] On Behalf Of
Ched
Sent: Sunday, July 09, 2017 12:01 PM
To: FPC-Pascal users discussions <fpc-pascal@lists.freepascal.org>
Subject: Re: [fpc-pascal] Fixed record files
Hello,
I'll try something like
If filesize(drawfile)>0 then
Seek(drawfile, sizeof(drawfile)-1)
else
"empty file";
For portability of you file and software, I recommand you to use a "packed
record" with an internal forced word-align of the double data. If size matters,
no need to align.
Type
DrawCMD = Record
GC: Byte;
__: byte; { no use axcept to force align on words for
speed on certain systems }
PX,PY,PZ,GX,GY,GZ,GI,GJ,R,SA,EA:Double;
End;
This can also be uses for memory access, as on some processors, word aligning
data can save some cpu cycles with reference to non aligned data for data
longer than one byte/char.
Chers, Ched
Le 09.07.2017 à 13:45, James Richters a écrit :
> I have a few questions about fixed record files. I have the following:
>
> Type
>
> DrawCMD = Record
>
> GC: Byte;
>
> PX,PY,PZ,GX,GY,GZ,GI,GJ,R,SA,EA:Double;
>
> End;
>
> Var
>
>DrawFile: File Of DrawCMD;
>
>Drawinfo: DrawCMD;
>
> I wish to get to the end of the file and read the last record. Currently I
> am doing it like this:
>
> Reset(DrawFile);
>
> while not eof(DrawFile) do
>
> begin
>
> Read(DrawFile,DrawInfo);
>
> End;
>
> When this finishes Drawinfo contains the last record of the file. But
> I’m wondering if there is a better way since it’s a file of fixed records.
>
> I’m also wondering if there is a way to insert a record at the
> beginning of the file, or in the middle of the file without doing
> something like copying the entire file to a temp file, then re-writing the
> entire new file in the desired order?
>
> James
>
>
>
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Re: [fpc-pascal] Fixed record files
Hello,
I'll try something like
If filesize(drawfile)>0 then
Seek(drawfile, sizeof(drawfile)-1)
else
"empty file";
For portability of you file and software, I recommand you to use a "packed record" with an internal
forced word-align of the double data. If size matters, no need to align.
Type
DrawCMD = Record
GC: Byte;
__: byte; { no use axcept to force align on words for
speed on certain systems }
PX,PY,PZ,GX,GY,GZ,GI,GJ,R,SA,EA:Double;
End;
This can also be uses for memory access, as on some processors, word aligning data can save some cpu
cycles with reference to non aligned data for data longer than one byte/char.
Chers, Ched
Le 09.07.2017 à 13:45, James Richters a écrit :
I have a few questions about fixed record files. I have the following:
Type
DrawCMD = Record
GC: Byte;
PX,PY,PZ,GX,GY,GZ,GI,GJ,R,SA,EA:Double;
End;
Var
DrawFile: File Of DrawCMD;
Drawinfo: DrawCMD;
I wish to get to the end of the file and read the last record. Currently I am
doing it like this:
Reset(DrawFile);
while not eof(DrawFile) do
begin
Read(DrawFile,DrawInfo);
End;
When this finishes Drawinfo contains the last record of the file. But I’m wondering if there is a better
way since it’s a file of fixed records.
I’m also wondering if there is a way to insert a record at the beginning of the file, or in the middle of
the file without doing something like copying the entire file to a temp file, then re-writing the entire
new file in the desired order?
James
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