How to get drive letter of a USB memory stick drive given its volume label? - windows

Question

A USB memory stick has two partitions - one read only and the other read-write.
My program runs from the read-only partition.
The volume labels for both partitions are fixed by the manufacturer:
MYDISK-RO and MYDISK-RW
When inserted in Windows, each partition (volume) gets a different drive letter. These drive letters are different on different computers depending on the configuration ie. the number of drive letters already allocated to disk drives.
My question is:
Which is the best (most efficient) way for the program to find the drive letter of the read-write partition, using the volume label?
It needs to work on Windows XP and up.
Rather than enumerate all drive letters and compare the volume label to the one that we need, I'm looking ideally for a single function call to Windows .. something like:
GetDriveLetterByVolumeName(AVolumeLabel: String);
or
GetVolumeInformation(AVolumeLabel: String);
Is there such a function or is enumerating the drive letters and comparing each volume label the only solution?
TIA.

Answer 1

Long long time ago I used this code (Was on Delphi7)
This procedure add in combobox all the root of all Removable drives found
Procedure TfMain.GetDiskDrives();
var
r: LongWord;
Drives: array[0..128] of char;
pDrive: pchar;
begin
Result := '';
r := GetLogicalDriveStrings(sizeof(Drives), Drives);
if r = 0 then exit;
if r > sizeof(Drives) then
raise Exception.Create(SysErrorMessage(ERROR_OUTOFMEMORY));
pDrive := Drives; // Point to the first drive
while pDrive^ <> #0 do begin
if GetDriveType(pDrive) = DRIVE_REMOVABLE then begin
cDrive.Items.Add(pDrive);
end;
inc(pDrive, 4); // Point to the next drive
end;
if cDrive.Items.Count=1 then cDrive.ItemIndex:=0;
end;
After that you can use the following function to get the volume name
function GetVolumeName(DriveLetter: Char): string;
var
dummy: DWORD;
buffer: array[0..MAX_PATH] of Char;
oldmode: LongInt;
begin
oldmode := SetErrorMode(SEM_FAILCRITICALERRORS);
try
GetVolumeInformation(PChar(DriveLetter + ':\'),
buffer,
SizeOf(buffer),
nil,
dummy,
dummy,
nil,
0);
Result := StrPas(buffer);
finally
SetErrorMode(oldmode);
end;
end;

Answer 2

I'm posting my code adapted from Gianluca Colombo's answer:
Tested and working with Delphi XE2 Update 4.1 on Windows 7 x64.
unit uDiskUtils;
interface
uses Windows, Classes, SysUtils;
Procedure GetDiskDrives(var ADriveList: TStrings);
function GetVolumeName(const ADriveLetter: Char): string;
function FindDiskDriveByVolumeName(const AVolumeName: String): Char;
implementation
Procedure GetDiskDrives(var ADriveList: TStrings);
var
r: LongWord;
Drives: array [0 .. 128] of Char;
pDrive: pchar;
begin
ADriveList.Clear;
r := GetLogicalDriveStrings(sizeof(Drives), Drives);
if r = 0 then
exit;
if r > sizeof(Drives) then
raise Exception.Create(SysErrorMessage(ERROR_OUTOFMEMORY));
pDrive := Drives; // Point to the first drive
while pDrive^ <> #0 do
begin
if GetDriveType(pDrive) = DRIVE_REMOVABLE then
begin
ADriveList.Add(pDrive);
end;
inc(pDrive, 4); // Point to the next drive
end;
end;
function GetVolumeName(const ADriveLetter: Char): string;
var
dummy: DWORD;
buffer: array [0 .. MAX_PATH] of Char;
oldmode: LongInt;
begin
oldmode := SetErrorMode(SEM_FAILCRITICALERRORS);
try
GetVolumeInformation(pchar(ADriveLetter + ':\'), buffer, sizeof(buffer), nil, dummy, dummy, nil, 0);
Result := StrPas(buffer);
finally
SetErrorMode(oldmode);
end;
end;
function FindDiskDriveByVolumeName(const AVolumeName: String): Char;
var
dl: TStringList;
c: Integer;
begin
Result := ' ';
dl := TStringList.Create;
try
GetDiskDrives(TStrings(dl));
for c := 0 to dl.Count - 1 do
if (AVolumeName = GetVolumeName(dl[c][1])) then
Result := dl[c][1];
finally
dl.Free;
end;
end;
end.