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How do I compress a file (under NT4)???

cdms
cdms asked
on
Medium Priority
583 Views
Last Modified: 2008-02-01
As I understand it the following code should compress a file using the standard NT file compression, but it does not work.  Any ideas???

Also does anyone know which unit I need to get the value for FSCTL_SET_COMPRESSION - I write a small C program to display this constant to get its value as it did not seem to be defined in the Windows stuff.

I have removed the error processing to minimise the code I need to post.

Regards

Dave

procedure FCompress(pathname: string);
const
   comp_buflen = 16384;       // 16K buffer

var
   TFifile:          TFileStream;
   comp_buffer:      Pchar;
   comp_result:      Boolean;
   BytesReturned:    LongInt;

begin
    comp_buffer := nil;

    GetMem(comp_buffer, comp_buflen);

    TFIfile := TFileStream.create(pathname,
               fmOpenReadWrite and fmShareDenyWrite);

    comp_result := deviceIOControl(TFifile.Handle,
       $09c040, // This should be FSCTL_SET_COMPRESSION,
                // but this constant seems to have been
               // omitted from the Delphi libraries
       comp_buffer,
       comp_buflen,
       nil,
       0,
       BytesReturned,
       nil);

    TFIfile.Free;
    FreeMem(comp_buffer);
    comp_buffer := nil;

end;
Comment
Watch Question

why not use this component with source code found at DSP: http://sunsite.icm.edu.pl/delphi/ftp/d10free/tlzrw1.zip

Guess it should do the job


Author

Commented:
Sorry, but a component is overkill for this purpose, and does answer the main point of my question - where have I gone wrong???

Author

Commented:
Having looked at the component Rene suggested, I note that this ia a component to compress a file into an archive.  Just to clarify, this is NOT what I want.

All I want to be able to do is turn on the NTFS compression attribute, compressing the file in situ.

Hope this helps...

Dave

Commented:
In the FindFirst, the attribute value for the compressed files is 2048 ($800). However, Microsoft say it's 128 ($80)..... (i've never obtain this value).

Author

Commented:
I dont want to find the compressed files.  I want to compress them!!!

However, I found the answer elsewhere.  The code should read...

procedure FCompress(pathname: string);
const
   comp_buflen = sizeof(Integer);
var
   TFifile:          TFileStream;
   comp_buffer:      Integer;
   comp_result:      Boolean;
   BytesReturned:    LongInt;

begin
    comp_buffer := 1; // NT default compression

    TFIfile := TFileStream.create(pathname,
               fmOpenReadWrite and fmShareDenyWrite);

    comp_result := deviceIOControl(TFifile.Handle,
       $09c040, // This should be FSCTL_SET_COMPRESSION,
                // but this constant seems to have been
                // omitted from the Delphi libraries
       Pointer(@comp_buffer),
       comp_buflen,
       nil,
       0,
       BytesReturned,
       nil);

    TFIfile.Free;
end;

Commented:
I have understand what you mean, but have you try the value 2048 and 128 for FSCTL_SET_COMPRESSION? You should know that Microsoft use different names for the same values depending on where they are. That's why i'gave you the corresponding values for another function.

Author

Commented:
This value is actually very specific, and is a bit-mapped value with four different components. The value of 9c040 (hex) is correct.
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