NTFS file compression
I need to compress a file on an NTFS volume using NT's compression attributes. It can't be done by changing the compressed attribute (2048). I've found API calls CreateFile and DeviceIoControl can do the trick, but I cant get them to work correctly.
Which one doesn't work?
ASKER
I got this line of C code which apparently does the trick:
bRet = DeviceIoControl(hFile, FSCTL_SET_COMPRESSION, &uMode, sizeof(uMode), NULL, 0, &dwAttributes, NULL)
Can't getit to work with VB as:
nRet = DeviceIoControl(nHandle, &HD0003, nMode, 4&, 0&, 4&, 0&, 0&)
Tried various combinations of parameters.
bRet = DeviceIoControl(hFile, FSCTL_SET_COMPRESSION, &uMode, sizeof(uMode), NULL, 0, &dwAttributes, NULL)
Can't getit to work with VB as:
nRet = DeviceIoControl(nHandle, &HD0003, nMode, 4&, 0&, 4&, 0&, 0&)
Tried various combinations of parameters.
Maybe just write a dll and call it from vb
That's not a very good answer - with a few rare exceptions if it can be done from a DLL it can be done from VB.
pokrakam, I just figured out how to do it - I'll post the code as soon as I can post it as an answer (i.e. as soon as you reject the current one). What you had is close, who knows, maybe by the time you read this you might have figured it out. (If so, please give me a chance to post the answer anyway and get the points, since I spent a lot of time figuring this one out). Thanks!
pokrakam, I just figured out how to do it - I'll post the code as soon as I can post it as an answer (i.e. as soon as you reject the current one). What you had is close, who knows, maybe by the time you read this you might have figured it out. (If so, please give me a chance to post the answer anyway and get the points, since I spent a lot of time figuring this one out). Thanks!
ASKER
alamo's comment was about the most useful answer thus far, so I'll reopen the question.
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ASKER
Sorry about delay - 'puter got trashed, back online now.
All workes fine - I'd love to know where you got
FSCTL_SET_COMPRESSION As Long = &H9C040
from???
All workes fine - I'd love to know where you got
FSCTL_SET_COMPRESSION As Long = &H9C040
from???
I computed FSCTL_SET_COMPRESSION from the header file definitions. I did however, compute it the first time incorrectly (as &HD0003, same as you). Having seen &HD0003 in your post I didn't question my initial computation and wasted 2-3 hours trying things. Then I went back and double-checked and found that in:
#define CTL_CODE( DeviceType, Function, Method, Access )
(((DeviceType) << 16) | ((Access) << 14) | ((Function) << 2) | Method))
the order of the arguments and the order they are used are different, the middle two are swapped. If you don't notice they are swapped you get &HD003. When you do eventually notice you get
the right answer... oh well.
#define CTL_CODE( DeviceType, Function, Method, Access )
(((DeviceType) << 16) | ((Access) << 14) | ((Function) << 2) | Method))
the order of the arguments and the order they are used are different, the middle two are swapped. If you don't notice they are swapped you get &HD003. When you do eventually notice you get
the right answer... oh well.