Question
I need to know if my program can write files to the disk (HDD, floppy, flash, CD) from where it is running. I have tried something like:
{$I-}
Rewrite(myFile);
{$I+}
Result:= (IOResult = 0);
The problem is that if the disk is read-only, Windows gives me an error message telling me that
"appName.exe - Write Protect Error The disk cannot be written to because it is write protected. Please remove the write protection from the volume USB_BOOT in drive D:. Cancel TryAgain Continue"
How can I test for write access without raising any error/warning messages? Thanks.
Edit:
Ok. The "bug" has nothing to do with the above mentioned piece of code. I only thought that it appears there. I move the code to the read-only disk and ran it from there. The bug appears in a function called "CreateShortcutEx", on this line:
MyPFile.Save(PWChar(WFileName),False);
MyPFile is declared like this:
var
MyObject : IUnknown;
MySLink : IShellLink;
MyPFile : IPersistFile;
Directory : String;
WFileName : WideString;
MyReg : TRegIniFile;
begin
MyObject := CreateComObject(CLSID_ShellLink);
MySLink := MyObject as IShellLink;
MyPFile := MyObject as IPersistFile;
.....
end;
So, why is MyPFile trying to write to the application's drive (the one that is read-only) if the WFileName parameter is "C:\documents and settings\bla bla" ?
Solution
Call the Windows API SetErrorMode() function to disable the error message box.
Edit:
I just tried, and this:
procedure TForm1.Button1Click(Sender: TObject);
var
Str: TStream;
OldMode: Cardinal;
begin
OldMode := SetErrorMode(SEM_FAILCRITICALERRORS);
try
try
Str := TFileStream.Create('z:\foo.txt', fmOpenReadWrite);
try
finally
Str.Free;
end;
except end;
finally
SetErrorMode(OldMode);
end;
end;
works as expected.
OTHER TIPS
Not really pretty but this seems to work for me.
function CanWrite(drive: string): boolean;
var
OldMode: Cardinal;
begin
OldMode := SetErrorMode(SEM_FAILCRITICALERRORS);
try
with TStringList.Create do
try
SaveToFile(drive + ':\file.txt');
result := true;
try
deletefile(drive + ':\file.txt');
except
end;
except
result := false;
end;
finally
SetErrorMode(OldMode);
end;
end;
Call to it with
if CanWrite('g') = true then
begin
showmessage('Can Write');
end
else
begin
showmessage('Can not write');
end;
What happens when you put your code inside an try/except?
Also, you can try (something like) this:
function CanWrite: boolean;
begin
result := true;
with TStringList.Create do
try
SaveToFile('file.txt');
except
result := false;
finally
Free;
end;
end;
Sorry, but I don't code in Delphi anymore and I don't have Delphi installed anywhere.
There exist a small freeware "Drive ready?" utility (dready.com) written by Horst Schaeffer that also can check write access. I have not tested it but as far as I can see this could be used as a solution; call it for instance as "DREADY C: /W" and check the return value.