Table in landscape mode

Question

I would to make the table in landscape mode. To do that, I used pdflscape package. But I couldn't get the desired result. How to do that?

Here is the MWE:

\documentclass[12pt]{article}
\usepackage{xtab,caption}
\usepackage{pdflscape}
\newcommand\Lenv{\textsf}
\begin{document}
\begin{landscape}
\topcaption{The principal xtab package commands} \label{tab:xtab}
\tablefirsthead{\hline \multicolumn{1}{|c|}{\textbf{Command}} &
\multicolumn{1}{c|}{\textbf{Effect}} \\ \hline }
\tablehead{\multicolumn{2}{c}%
{{\captionsize\bfseries \tablename\ \thetable{} --
continued from previous page}} \\
\hline \multicolumn{1}{|c|}{\textbf{Command}} &
\multicolumn{1}{c|}{\textbf{Effect}} \\ \hline }
\tablelasthead{\multicolumn{2}{c}%
{{\captionsize\bfseries \tablename\ \thetable{} --
concluded from previous page}} \\
\hline \multicolumn{1}{|c|}{\textbf{Command}} &
\multicolumn{1}{c|}{\textbf{Effect}} \\ \hline }
\tabletail{\hline \multicolumn{2}{|r|}{{Continued on next page}} \\ \hline}
\tablelasttail{\hline \hline}
\begin{center}
\begin{xtabular}{|l|p{0.5\textwidth}|}
\verb|\begin{xtabular}{...}| & This is equivalent to the normal
\verb|\begin{tabular}{...}| environment.
You supply the specification of the columns
just as for the normal \Lenv{tabular} environment.
\\
&
All commands that can be used within a \Lenv{tabular}
environment can also be used within
the \Lenv{xtabular} environment.
\\
&
Unlike the \Lenv{tabular} environment which prevents page breaking
within the tabular, the \Lenv{xtabular} allows page breaking, so that
tabulars can extend automatically across several pages.
... ... ...\\
\verb|\tablelasttail{...}| & The contents of this command are inserted before
the final (internal) \verb|\end{tabular}| of the table.
\\
&
For example, you might want to note that this is where
the table ends.
\\
\end{xtabular}
\end{center}
\end{landscape}
\end{document} 

Answer 1

use

 \begin{xtabular}{|l|p{0.5\linewidth}|}

lscape does not change \textwidth in the landscape environment.

Answer 2

Another option is to use \textheight. Since with landscape, text height and text width are not swapped, the width of the table is along the text height. Put proper value in 0.9\textheight:

\documentclass[12pt]{article}
\usepackage{xtab,caption}
\usepackage{pdflscape}
\newcommand\Lenv{\textsf}
\begin{document}
\begin{landscape}
\topcaption{The principal xtab package commands} \label{tab:xtab}
\tablefirsthead{\hline \multicolumn{1}{|c|}{\textbf{Command}} &
\multicolumn{1}{c|}{\textbf{Effect}} \\ \hline }
\tablehead{\multicolumn{2}{c}%
{{\captionsize\bfseries \tablename\ \thetable{} --
continued from previous page}} \\
\hline \multicolumn{1}{|c|}{\textbf{Command}} &
\multicolumn{1}{c|}{\textbf{Effect}} \\ \hline }
\tablelasthead{\multicolumn{2}{c}%
{{\captionsize\bfseries \tablename\ \thetable{} --
concluded from previous page}} \\
\hline \multicolumn{1}{|c|}{\textbf{Command}} &
\multicolumn{1}{c|}{\textbf{Effect}} \\ \hline }
\tabletail{\hline \multicolumn{2}{|r|}{{Continued on next page}} \\ \hline}
\tablelasttail{\hline \hline}
\begin{center}
\begin{xtabular}{|l|p{0.9\textheight}|}
\verb|\begin{xtabular}{...}| & This is equivalent to the normal
\verb|\begin{tabular}{...}| environment.
You supply the specification of the columns
just as for the normal \Lenv{tabular} environment.
\\
&
All commands that can be used within a \Lenv{tabular}
environment can also be used within
the \Lenv{xtabular} environment.
\\
&
Unlike the \Lenv{tabular} environment which prevents page breaking
within the tabular, the \Lenv{xtabular} allows page breaking, so that
tabulars can extend automatically across several pages.
... ... ...\\
\verb|\tablelasttail{...}| & The contents of this command are inserted before
the final (internal) \verb|\end{tabular}| of the table.
\\
&
For example, you might want to note that this is where
the table ends.
\\
\end{xtabular}
\end{center}
\end{landscape}
\end{document}