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truncate from down to up

Posted on 2003-12-02
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Last Modified: 2012-05-04
how i can create function, which delete from file line which is first

whis delete line from last

  AssignFile(F, DBname);
  Reset(F);
  Seek(F, FileSize(F)-1);
  Truncate(F);
  CloseFile(F);

I need the same but from first record to last
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Question by:bulbul2
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9 Comments
 
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Accepted Solution

by:
roknjohn earned 20 total points
ID: 9859470
it takes longer because you have to move each record up.  One way is:

  AssignFile(F, DBname);
  Reset(F);
  for i := 0 to FileSize(f)-2 do begin
    Seek(F, i+1);
    Read(F,X);
    Seek(F, i);
    Write(F,X);
  end;
  Seek(F, FileSize(F)-1);
  Truncate(F);
  CloseFile(F);

If the file is small, you can just read the whole file in, then write it out again (less the first record, of course).
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LVL 27

Expert Comment

by:kretzschmar
ID: 9859486
copy the last record over the first (or any before last) record,
and truncate the file as above

meikl ;-)
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Expert Comment

by:roknjohn
ID: 9859540
>>copy the last record over the first

That would work, but it wouldn't preserve the record order of the file, which I assumed was important.  

I like your thinking, though. :-)
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LVL 27

Expert Comment

by:kretzschmar
ID: 9859793
:-))
usual i do so on sequential files,
because its the fast solution,
but as you stated, it will dissort the recordorder

take also a look to this q
http://www.experts-exchange.com/Programming/Programming_Languages/Delphi/Q_20147576.html

meikl ;-)
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LVL 5

Expert Comment

by:delphized
ID: 9864809
To have best performance you should act in this way: put a flag in your rows and virtually delete a row with marking this flag.
when you want to phisically delete the records marked (shrink the file) you make a new file and copy all the records not marked to it.
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Expert Comment

by:kretzschmar
ID: 9864824
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LVL 5

Expert Comment

by:delphized
ID: 9896815
And so...?..
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Expert Comment

by:-Karamja-
ID: 12382178
No comment has been added to this question in more than 21 days, so it is now classified as abandoned..
I will leave the following recommendation for this question in the Cleanup topic area:
Accept: roknjohn

Any objections should be posted here in the next 4 days. After that time, the question will be closed.

Karamja (Alan)
EE Cleanup Volunteer
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