%% 
%%  A DANTE-Edition example
%% 
%%  Example 04-01-6 on page 130.
%% 
%%  Copyright (C) 2010 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
\documentclass[]{article}
\pagestyle{empty}
\setlength\textwidth{201.70511pt}
\usepackage[utf8]{inputenc}% adapt maybe
\setlength\parindent{0pt}
\setlength\textwidth{6cm}

\usepackage{longtable,calc}

\begin{document}
left \hfill centred \hfill right
\setlength\LTleft{0pt}
\begin{longtable}{|l|c|r|p{1.5cm}|}\hline
left & centred & right & box\\\hline
l & c & r & p\{1.5cm\}\\\hline
\end{longtable}
\setlength\LTleft{\fill}\setlength\LTright{0pt}
\hfill right-aligned
\begin{longtable}{|l|c|r|p{1.5cm}|}\hline
left & centred & right & box\\\hline
l & c & r & p\{1.5cm\}\\\hline
\end{longtable}
\setlength\LTleft{\fill}\setlength\LTright{\fill}
\centerline{centred}
\begin{longtable}{|l|c|r|p{1.5cm}|}\hline
left & centred & right & box\\\hline
l & c & r & p\{1.5cm\}\\\hline
\end{longtable}
\end{document}