Get GUID of specific drive - windows

Question

I would like to find out the Drive-GUID for a specific drive letter.
I have following code:
Function GetVolumeNameForVolumeMountPoint(lpszVolumeMountPoint: LPCTSTR; lpszVolumeName: LPTSTR; cchBufferLength: DWORD): BOOL; stdcall;
external 'kernel32.dll' name 'GetVolumeNameForVolumeMountPointW';
procedure TForm1.Button1Click(Sender: TObject);
var
Buffer: array[0..50] of AnsiChar;
begin
if GetVolumeNameForVolumeMountPoint('C:\', Buffer, SizeOf(Buffer)) then
begin
showmessage(buffer); // Expected: "\\?\Volume{deadbeef-895e-4a1d-9d64-9b82fa068d76}\"
end
else RaiseLastOSError; // Actual: ERROR_INVALID_NAME (123).
end;
I am getting the error ERROR_INVALID_NAME (123), but I do not know why. What am I doing wrong?

Answer 1

You are calling the Unicode version of the function but passing ANSI text. Thus the first argument you pass is wrongly encoded and hence the error message.
This program demonstrates how it should be done:
{$APPTYPE CONSOLE}
uses
SysUtils, Windows;
function GetVolumeNameForVolumeMountPointA(lpszVolumeMountPoint: PAnsiChar;
lpszVolumeName: PAnsiChar; cchBufferLength: DWORD): BOOL; stdcall;
external 'kernel32.dll';
procedure Main;
var
Buffer: array [0 .. 49] of AnsiChar;
begin
Win32Check(GetVolumeNameForVolumeMountPointA('C:\', Buffer, Length(Buffer)));
Writeln(Buffer);
end;
begin
try
Main;
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
Readln;
end.
Since it is clear that you are using a pre-Unicode version of Delphi (otherwise your program would not compile), I have given you ANSI code above. If you ever upgrade to a Unicode version of Delphi then you'd write it like this:
{$APPTYPE CONSOLE}
uses
SysUtils, Windows;
function GetVolumeNameForVolumeMountPointW(lpszVolumeMountPoint: PWideChar;
lpszVolumeName: PWideChar; cchBufferLength: DWORD): BOOL; stdcall;
external 'kernel32.dll';
procedure Main;
var
Buffer: array [0 .. 49] of WideChar;
begin
Win32Check(GetVolumeNameForVolumeMountPointW('C:\', Buffer, Length(Buffer)));
Writeln(Buffer);
end;
begin
try
Main;
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
Readln;
end.
Or if you want code that works in all versions of Delphi, you can do this:
{$APPTYPE CONSOLE}
uses
SysUtils, Windows;
const
Win32ImportSuffix = {$IFDEF Unicode}'W'{$ELSE}'A'{$ENDIF};
function GetVolumeNameForVolumeMountPointA(lpszVolumeMountPoint: PAnsiChar;
lpszVolumeName: PAnsiChar; cchBufferLength: DWORD): BOOL; stdcall;
external 'kernel32.dll';
function GetVolumeNameForVolumeMountPointW(lpszVolumeMountPoint: PWideChar;
lpszVolumeName: PWideChar; cchBufferLength: DWORD): BOOL; stdcall;
external 'kernel32.dll';
function GetVolumeNameForVolumeMountPoint(lpszVolumeMountPoint: PChar;
lpszVolumeName: PChar; cchBufferLength: DWORD): BOOL; stdcall;
external 'kernel32.dll' name 'GetVolumeNameForVolumeMountPoint' + Win32ImportSuffix;
procedure Main;
var
Buffer: array [0 .. 49] of Char;
begin
Win32Check(GetVolumeNameForVolumeMountPoint('C:\', Buffer, Length(Buffer)));
Writeln(Buffer);
end;
begin
try
Main;
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
Readln;
end.