c++ - GetLogicalDrives() for loop

Question

I am new to the win32 api and need help trying to understand how the GetLogicalDrives() function works. I am trying to populate a cbs_dropdownlist with all the available drives that are not in use. here is what I have so far. I would appreciate any help.

void FillListBox(HWND hWndDropMenu)
{
 DWORD drives = GetLogicalDrives();
 for (int i=0; i<26; i++)
 {
    SendMessage(hWndDropMenu, CB_ADDSTRING, 0, (LPARAM)drives);
 }
}

Answer 1

The function GetLogicalDrives returns a bitmask of the logical drives available. Here is how you would do it:

 DWORD drives = GetLogicalDrives();
 for (int i=0; i<26; i++)
 {
    if( !( drives & ( 1 << i ) ) )
    {
       TCHAR driveName[] = { TEXT('A') + i, TEXT(':'), TEXT('\'), TEXT('') };
       SendMessage(hWndDropMenu, CB_ADDSTRING, 0, (LPARAM)driveName);
    }
 }

The code checks whether the i-th bit in the bitmask is not set to 1 or true.