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Checking if a drive is ready for access?

Posted on 1998-11-01
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Last Modified: 2010-04-06
What is the best way to test if a drive is ready for access? This is needed for drives like cd-roms and jaz drives.

Thanks!
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Question by:Kmiller
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Expert Comment

by:philipleighs
ID: 1345316
Hi,

Here is a snippet of code that may help.
The important point is the SetErrorMode calls. Without these, (and when running outside Delphi), and when the a: drive is not ready you get a message saying "System error, drive not ready, Abort, Retry, Cancel.
The SetErrorMode supresses these error messages.
You can then call DiskFree. There may be something better than DiskFree, but if it returns -1 then the drive is not ready.

PrevErrorMode := SetErrorMode(SEM_FAILCRITICALERRORS);
try
   if DiskFree(1) <> -1 then
      //A: Drive is ready
   else
      //A: drive is not ready
finally
  SetErrorMode(PrevErrorMode);
end;

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Author Comment

by:Kmiller
ID: 1345317
how would this be done when you only have the drive letter? Say M:\ which is a cdrom drive.
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Expert Comment

by:philipleighs
ID: 1345318
//'A' or 'a' returns 1,
//'B' or 'b' returns 2 etc
function GetDriveNumber(Letter: Char): Integer;
begin
  Result := Ord(UpCase(Letter)) - Ord('A') + 1;
end;


begin
DiskFree(   GetDriveNumber('M')  );
.

Note if you have a string, you could also use GetDriveNumber like this:

s := 'M:\';
DiskFree(   GetDriveNumber(  s[1]  );

Cheers,
Phil.

PS: Tell me if you want code that tells you which drives(s) are CD-ROMs then I'll can paste it here.

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Expert Comment

by:dwwang
ID: 1345319
This one is from Inprise's FAQ, it does not need to use try..except.

function IsDriveReady(DriveLetter : char) : bool;
                    var
                      OldErrorMode : Word;
                      OldDirectory : string;
                    begin
                      OldErrorMode := SetErrorMode(SEM_NOOPENFILEERRORBOX);
                      GetDir(0, OldDirectory);
                      {$I-}
                        ChDir(DriveLetter + ':\');
                      {$I+}
                       if IoResult <> 0 then
                        Result := False
                       else
                        Result := True;

                      ChDir(OldDirectory);
                      SetErrorMode(OldErrorMode);
                    end;
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Author Comment

by:Kmiller
ID: 1345320
Thanks! They both seem to work... someone answer for credit.
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dwwang earned 100 total points
ID: 1345321
Sorry for others ^_^
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Expert Comment

by:philipleighs
ID: 1345322
Hmm,

Don't you think the first answer is the one that deserves the credit?
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Expert Comment

by:dwwang
ID: 1345323
Hi, I just happened to be notified by e-mail and come here to make an answer, if you care of that, now I just ask Kmiller to reject my answer.
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