Nested tabularx inside a \newenvironment

Question

I would like to use tabularx in my own environment, but nested inside a table environment.

Please see my MWE below: I first produce the desired result without a custom environment. Then I try to accomplish the same output with my own environment. Alas that doesn't work:

When I switch from tabular* to tabularx, I get the compile error File ended while scanning use of \TX@get@body.. If I stay with tabular*, but switch the last column descriptor from c to X, I get another compile error: Extra alignment tab has been changed to \cr. a & b &.

In the answer to question tabularx inside a \newenvironment, one suggests to go for \tabularx and \ endtabularx, but that doesn't work in my case where tabularx is nested inside a table environment.

What am I doing wrong?

\documentclass{article}
\usepackage{tabularx}
\begin{document}
\begin{table}[!h]
  \begin{tabularx}{\textwidth}{|c|c|X|}\hline
    a & b & tabularx \\hline
  \end{tabularx}
\end{table}
\newenvironment{MyTabular}{
  \begin{table}[!h]
    \begin{tabular}{\textwidth}{|c|c|c|}\hline
    }{%
      \hline
    \end{tabular}
  \end{table}
}
\begin{MyTabular}
  a & b & MyTabular \
\end{MyTabular}
\end{document}

Why would you use table if you don't add a caption? There's no law imposing that a tabular (or variant thereof) must live inside table. — egreg, Oct 19 '23 at 13:51
The instruction \begin{tabular*}{\textwidth}{|c|c|c|} looks suspect for two separate reasons. First, you're not providing any mechanism that would enable LaTeX to achieve your goal of making the width of the tabular* environment equal \textwidth. Second, never use vertical rules in a proper tabular* environment. In short, I think you should replace \begin{tabular*}{\textwidth}{|c|c|c|} with \begin{tabular*}{\textwidth}{@{\extracolsep{\fill}}ccc @{}}. — Mico, Oct 19 '23 at 17:03
@egreg I provided a MWE. For that I needed a nested environment. In my real world document, tabularx is nested inside a table to which I do supply both a caption and a label ... both of which are totally unnessary in the context of my question. Hence MWE. — Markus Nißl, Oct 20 '23 at 08:26
@Mico I provided a MWE that compiles and that demonstrates that either going for the column descriptor X or for tabularx in my custom environment breaks compilation. As indicated in my introduction, the aim is to use tabularx with X inside my custom environment. — Markus Nißl, Oct 20 '23 at 08:29

campa · Accepted Answer · 2023-10-19T14:01:05.463

4

tabularx gathers everything up to the next \end{⟨current environment⟩}, and the name of the current environment is set up by \begin{...}. Therefore, if you do only

\newenvironment{MyTabular}{
  \begin{table}[!h]
    \tabularx{\textwidth}{|X|X|X|}\hline
    }{%
      \hline
    \endtabularx
  \end{table}
}

then \begin{MyTabular} will first save MyTabular as current environment name, but then \begin{table} changes the name of the current environment to table; tabularx tries to look up everything up to \end{table}, which it won't find, hence the errors.

You should use also \table and \endtable

\documentclass{article}
\usepackage{tabularx}
\newenvironment{MyTabular}[1][tbp]{% use !h as default only if you like pain
  \table[#1]
  \tabularx{\textwidth}{|X|X|X|}
  \hline
  }{%
   \% <-- I'd put this here, so you don't have to close every tabular with \
   \hline
   \endtabularx
   \endtable
}
\begin{document}
\begin{MyTabular}
  a & b & MyTabular
\end{MyTabular}
\end{document}

EDIT After egreg's comment it came to me that you might be wanting to place the table where it is written in the code but you don't need a caption. In this case there is no need for a table environment, you can just use center (which adds a bit of space above and below).

\newenvironment{MyTabular}{%
  \center
  \tabularx{\textwidth}{|X|X|X|}
  \hline
  }{%
   \\% <-- I'd put this here, so you don't have to close every tabular with \\
   \hline
   \endtabularx
   \endcenter
}

edited Oct 19 '23 at 14:01

answered Oct 19 '23 at 13:33

campa

31,130

The default placement should never be !h. – egreg Oct 19 '23 at 13:50
@egreg I agree but I don't feel entirely responsible for other people's bad habits ;-) I'll add a comment. – campa Oct 19 '23 at 13:52
+1 for your answer. – Sebastiano Oct 19 '23 at 21:18
@egreg @campa I provided a MWE. !h puts both tables underneath each other at the top of the document. Otherwise they would have been spread of the page. I intentionally used !h for the sake of a nice MWE. – Markus Nißl Oct 20 '23 at 08:33
@campa Thanks for pointing out that \begin{...} has an influence on the \newenvironment command. This is crucial to know and hence to understand why the original approach was not working. This was the only answer I was looking for. Thank you! – Markus Nißl Oct 20 '23 at 08:38
@MarkusNißl !h is still wrong (and LaTeX will replace it by !ht automatically). Note that it is often unwise to not include p in the possible placements, as otherwise you might get your floats flushed to the end of the chapter/document. – Skillmon Oct 23 '23 at 11:43

Nested tabularx inside a \newenvironment

1 Answers1