Detect an Windows Administrator Login

Windows with Delphi
Windows API (94)
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Detect an Windows Administrator Login

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If you develop certain applications that require an Administrator login for installation you will face yourself with this question - 'How can I know whether the current user is an Administrator' ?

Evaluating the user name is not sufficient, since any user can have Admin privileges.

The solution:

First off, one can try to detect whether the machine is running Windows 95/ 98/ ME. These operating systems have no concept of an 'Administrator'. In all other cases (NT, Win2000) you have to explicitely check the account privileges.

The code below does both, use it like this:

if isAdmin then
begin
ShowMessage('Logged in as Administrator');
end;

{$APPTYPE CONSOLE}
program isAdmin;

uses
  SysUtils, Windows, Forms;

{$R *.RES}

const
  SECURITY_NT_AUTHORITY: TSIDIdentifierAuthority =
    (Value: (0, 0, 0, 0, 0, 5));
  SECURITY_BUILTIN_DOMAIN_RID = $00000020;
  DOMAIN_ALIAS_RID_ADMINS     = $00000220;

// return TRUE for Admins (or Win95/98/ME)
function Is_Admin: Boolean;
var
  hAccessToken: THandle;
  ptgGroups: PTokenGroups;
  dwInfoBufferSize: DWORD;
  psidAdministrators: PSID;
  x: Integer;
  bSuccess: BOOL;
begin
  if Win32Platform <> VER_PLATFORM_WIN32_NT then
  begin
    Result := True;
    exit;
  end;

  Result := False;
  bSuccess := OpenThreadToken(GetCurrentThread, TOKEN_QUERY, True,
    hAccessToken);
  if not bSuccess then
  begin
    if GetLastError = ERROR_NO_TOKEN then
    bSuccess := OpenProcessToken(GetCurrentProcess, TOKEN_QUERY,
      hAccessToken);
  end;
  if bSuccess then
  begin
    GetMem(ptgGroups, 1024);
    bSuccess := GetTokenInformation(hAccessToken, TokenGroups,
      ptgGroups, 1024, dwInfoBufferSize);
    CloseHandle(hAccessToken);
    if bSuccess then
    begin
      AllocateAndInitializeSid(SECURITY_NT_AUTHORITY, 2,
        SECURITY_BUILTIN_DOMAIN_RID, DOMAIN_ALIAS_RID_ADMINS,
        0, 0, 0, 0, 0, 0, psidAdministrators);
      {$R-}
      for x := 0 to ptgGroups.GroupCount - 1 do
        if EqualSid(psidAdministrators, ptgGroups.Groups[x].Sid) then
        begin
          Result := True;
          break;
        end;
      {$R+}
      FreeSid(psidAdministrators);
    end;
    FreeMem(ptgGroups);
  end;
end;


begin
  if Is_Admin then
    Writeln(1)
  else
    Writeln(0);
end.

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