How to detect side when using `twoside`

Question

I would like to create a macro that creates a table with two columns. One thing should go into the inner column and another thing into the outer column, regardless of whether inner means left or right, so:

\newcommand{\testmacro}{
% On odd pages:
\begin{tabular}{lr}Inner text & Outer text\end{tabular}
% On even pages:
\begin{tabular}{lr}Outer text & Inner text\end{tabular}
}

Is there a way to achieve this?

Answer 1

Unfortunately the @lziminza's suggestion can fail:

\documentclass[twoside]{article}
\usepackage{ifoddpage}
\newcommand{\testmacro}{%
\checkoddpage
\ifoddpage
    \begin{tabular}{lr}Inner text & Outer text\end{tabular}
\else
    \begin{tabular}{lr}Outer text & Inner text\end{tabular}
\fi
}
\usepackage{blindtext}
\begin{document}
\blindtext[2]
\vskip 4\baselineskip
\blindtext[2]
\testmacro
\blindtext
\testmacro
\end{document}

results in:

on second page after two or more LaTeX runs.

To avoid this issue, you should at least prohibit page breaks between the \checkoddpage and \ifoddpage. I recommend to also explicitly allow page breaks before the \checkoddpage:

\documentclass[twoside]{article}
\usepackage{ifoddpage}
\newcommand{\testmacro}{%
% \par % could also be a good idea
  \pagebreak[1]
  \checkoddpage\nobreak
  \ifoddpage
    \begin{tabular}{lr}Inner text & Outer text\end{tabular}
  \else
    \begin{tabular}{lr}Outer text & Inner text\end{tabular}
  \fi
}
\usepackage{blindtext}
\begin{document}
\blindtext[2]
\vskip 4\baselineskip
\blindtext[2]
\testmacro
\blindtext
\testmacro
\end{document}

results in:

on second page.

Another suggestion would be to set a test label inside the tabular and do the test outside:

\documentclass[twoside]{article}
\usepackage{refcount}
\newcounter{testpage}
\newcommand{\testmacro}{%
  \ifodd \getpagerefnumber{testpage:\thetestpage}
    \begin{tabular}{lr}\label{testpage:\thetestpage}\stepcounter{testpage}Inner text & Outer text\end{tabular}
  \else
    \begin{tabular}{lr}\label{testpage:\thetestpage}\stepcounter{testpage}Outer text & Inner text\end{tabular}
  \fi
}
\usepackage{blindtext}
\begin{document}
\blindtext[2]
\testmacro
\vskip 3\baselineskip
\blindtext[2]
\testmacro
\blindtext
\testmacro
\end{document}

also works:

Answer 2

Use \usepackage{ifoddpage} package.

\newcommand{\testmacro}{
\checkoddpage
\ifoddpage
    \begin{tabular}{lr}Inner text & Outer text\end{tabular}
\else
    \begin{tabular}{lr}Outer text & Inner text\end{tabular}
\fi
}