{ 
  The NetGetDCName function returns the name of the primary domain controller (PDC). 
  It does not return the name of the backup domain controller (BDC) for the specified domain. 
  Also, you cannot remote this function to a non-PDC server. 
  Windows 2000/XP: Applications that support DNS-style names should call the  function. 
  Domain controllers in this type of environment have a multi-master 
  directory replication relationship. 
  Therefore, it may be advantageous for your application to use a DC that is not the PDC. 
  You can call the DsGetDcName function to locate any DC in the domain; 
  NetGetDCName returns only the name of the PDC. 
}
 
type
  EAccessDenied = Exception; 
  EInvalidOwner = Exception; 
  EInsufficientBuffer = Exception; 
  ELibraryNotFound = Exception; 
 
  NET_API_STATUS = Integer; 
 
const
  NERR_Success = 0; 
 
var
  NTNetGetDCName: function (Server, Domain: pWideChar; var DC: pWideChar): NET_API_STATUS; stdcall; 
  NTNetGetDCNameA: function (Server, Domain: PChar; var DC: PChar): NET_API_STATUS; stdcall; 
  NTNetApiBufferFree: function (lpBuffer: Pointer): NET_API_STATUS; stdcall; 
 
procedure NetCheck(ErrCode: NET_API_STATUS); 
begin
  if ErrCode <> NERR_Success then
  begin
    case ErrCode of
      ERROR_ACCESS_DENIED: 
        raise EAccessDenied.Create('Access is Denied'); 
      ERROR_INVALID_OWNER: 
        raise EInvalidOwner.Create('Cannot assign the owner of this object.'); 
      ERROR_INSUFFICIENT_BUFFER: 
        raise EInsufficientBuffer.Create('Buffer passed was too small'); 
      else
        raise Exception.Create('Error Code: ' + IntToStr(ErrCode) + #13 + 
          SysErrorMessage(ErrCode)); 
    end; 
  end; 
end; 
 
function GetPDC(szSystem: string): string; 
  { if szSystem = '' return the PDC else return DC for that domain }
const
  NTlib = 'NETAPI32.DLL'; 
  Win95lib = 'RADMIN32.DLL'; 
var
  pAnsiDomain: PChar; 
  pDomain: PWideChar; 
  System: array[1..80] of WideChar; 
  ErrMode: Word; 
  LibHandle: THandle; 
begin
  Result := ''; 
  LibHandle := 0; 
  try
    if Win32Platform = VER_PLATFORM_WIN32_NT then
    begin
      ErrMode := SetErrorMode(SEM_NOOPENFILEERRORBOX); 
      LibHandle := LoadLibrary(NTlib); 
      SetErrorMode(ErrMode); 
      if LibHandle = 0 then
        raise ELibraryNotFound.Create('Unable to map library: ' + 
          NTlib); @NTNetGetDCName := GetProcAddress(Libhandle, 'NetGetDCName'); 
        @NTNetApiBufferFree       := GetProcAddress(Libhandle, 
        'NetApiBufferFree'); 
      try
        if szSystem <> '' then
          NetCheck(NTNetGetDCName(nil, StringToWideChar(szSystem, @[Üye Olmadan Linkleri Göremezsiniz. Üye Olmak için TIKLAYIN...], 80), pDomain)) 
        else
          NetCheck(NTNetGetDCName(nil, nil, pDomain)); 
        Result := WideCharToString(pDomain); 
      finally
        NetCheck(NTNetApiBufferFree(pDomain)); 
      end; 
    end
    else
    begin
      ErrMode := SetErrorMode(SEM_NOOPENFILEERRORBOX); 
      LibHandle := LoadLibrary(Win95lib); 
      SetErrorMode(ErrMode); 
      if LibHandle = 0 then
        raise ELibraryNotFound.Create('Unable to map library: ' + 
          Win95lib); @NTNetGetDCNameA := GetProcAddress(Libhandle, 'NetGetDCNameA'); 
        @NTNetApiBufferFree := GetProcAddress(LibHandle, 'NetApiBufferFree'); 
      try
        if szSystem <> '' then
          NetCheck(NTNetGetDCNameA(nil, PChar(szSystem), pAnsiDomain)) 
        else
          NetCheck(NTNetGetDCNameA(nil, nil, pAnsiDomain)); 
        Result := StrPas(pAnsiDomain); 
      finally
        NetCheck(NTNetApiBufferFree(pAnsiDomain)); 
      end; 
    end; 
  finally
    if LibHandle <> 0 then
    begin
      FreeLibrary(Libhandle); // free handle if it has been allocated 
    end; 
  end; 
end; 
 
// Example call, Beispielaufruf: 
 
procedure TForm1.Button1Click(Sender: TObject); 
begin
  try
    Screen.Cursor  := crHourGlass; 
    label1.Caption := GetPDC(''); 
  finally
    Screen.Cursor := crDefault; 
  end; 
end;