Code:

function GetUserFromWindows: string;

var

UserName : string;

UserNameLen : Dword;

begin

UserNameLen := 255;

SetLength(userName, UserNameLen);

if GetUserName(PChar(UserName), UserNameLen) then

   Result := Copy(UserName,1,UserNameLen - 1)

else

   Result := '';

end;

Code:

function GetCurrentUserName: string;

const

  cnMaxUserNameLen = 254;

var

  sUserName: string;

  dwUserNameLen: DWORD;

begin

  dwUserNameLen := cnMaxUserNameLen - 1;

  SetLength(sUserName, cnMaxUserNameLen);

  GetUserName(PChar(sUserName), dwUserNameLen);

  SetLength(sUserName, dwUserNameLen);

  Result := sUserName;

end;

procedure TForm1.Button1Click(Sender: TObject);

begin

  ShowMessage(GetCurrentUserName);

end;

Code:

function GetCurrentUserName(var CurrentUserName: string): Boolean;

var

  BufferSize: DWORD;

  pUser: PChar;

begin

  BufferSize := 0;

  GetUserName(nil, BufferSize);

  pUser := StrAlloc(BufferSize);

  try

    Result := GetUserName(pUser, BufferSize);

    CurrentUserName := StrPas(pUser);

  finally

    StrDispose(pUser);

  end;

end;

procedure TForm1.Button1Click(Sender: TObject);

var

  CurrentUserName: string;

begin

  GetCurrentUserName(CurrentUserName);

  Label1.Caption :=  CurrentUserName;

end;

{*********************************************}

{

Windows NT/2000/XP:

The GetUserNameEx function retrieves the name of the user or other

security principal associated with the calling thread.

You can specify the format of the returned name.

If the thread is impersonating a client, GetUserNameEx

returns the name of the client.

}

const

  NameUnknown = 0; // Unknown name type.

NameFullyQualifiedDN = 1;  // Fully qualified distinguished name

NameSamCompatible = 2; // Windows NT® 4.0 account name

NameDisplay = 3;  // A "friendly" display name

NameUniqueId = 6; // GUID string that the IIDFromString function returns

NameCanonical = 7;  // Complete canonical name

NameUserPrincipal = 8; // User principal name

NameCanonicalEx = 9;

  NameServicePrincipal = 10;  // Generalized service principal name

DNSDomainName = 11;  // DNS domain name, plus the user name

procedure GetUserNameEx(NameFormat: DWORD;

  lpNameBuffer: LPSTR; nSize: PULONG); stdcall;

  external 'secur32.dll' Name 'GetUserNameExA';

function LoggedOnUserNameEx(fFormat: DWORD): string;

var

  UserName: array[0..250] of char;

  Size: DWORD;

begin

  Size := 250;

  GetUserNameEx(fFormat, @UserName, @Size);

  Result := UserName;

end;

procedure TForm1.Button1Click(Sender: TObject);

begin

  Edit1.Text := LoggedOnUserNameEx(NameSamCompatible);

end;