tabular multicolumn problem

[Jobst Hoffmann]

Hi all,

if I create a LaTeX-file like

--------8<---------------------------------------------
\documentclass{article}
\begin{document}

\begin{tabular}{cc}
\multicolumn{2}{c}{a}
\end{tabular}

\begin{tabular}{cc}
\input{mc}
\end{tabular}

\end{document}
--------8<---------------------------------------------

and a file mc.tex
--------8<---------------------------------------------
\multicolumn{2}{c}{a}
--------8<---------------------------------------------

the first tabular environment is formatted corrected, but the formatting
of the second tabular environment fails with an error message like

(./mc.tex
! Misplaced \omit.
\multispan ->\omit
\@multispan
l.1 \multicolumn{2}{c}{a}

?

Is there someone who can explain the behaviour to me (btw. inputting
other things into tabular environment works fine) and give a hint to
avoid that error?

Thanks in advance!
Jobst

[Ulrike Fischer]

\multicolumn must be the very first thing in a cell. You can't put
commands like \input inbetween.

--
Ulrike Fischer

[Heiko Oberdiek]

Ulrike Fischer <ne...@nililand.de> wrote:

> > \begin{tabular}{cc}
> > \input{mc}
> > \end{tabular}

> > and a file mc.tex

> > --------8<---------------------------------------------
> > \multicolumn{2}{c}{a}
> > --------8<---------------------------------------------
> >
> > the first tabular environment is formatted corrected, but the formatting
> > of the second tabular environment fails with an error message like
> >
> > (./mc.tex
> > ! Misplaced \omit.
> > \multispan ->\omit
> > \@multispan
> > l.1 \multicolumn{2}{c}{a}
> >
> > ?
> >
> > Is there someone who can explain the behaviour to me (btw. inputting
> > other things into tabular environment works fine) and give a hint to
> > avoid that error?
>
> \multicolumn must be the very first thing in a cell. You can't put
> commands like \input inbetween.

Especially LaTeX's version of \input is not expandable and such
non-expandable stuff will be the first thing in the cell.
The original \input as TeX primitive is expandable. That can be used
(LaTeX stores it in \@@input). But the syntax is the syntax of the
original TeX primitive and it doesn't provide LaTeX's error handling
for non-existing files.

\begin{tabular}{cc}
\csname @@input\endcsname mc %
\end{tabular}

But I think, a better solution would be, if the \begin and \end stuff
is also put into the file mc.tex.

Yours sincerely
Heiko <ober...@uni-freiburg.de>

[Jobst Hoffmann]

Thank you for your advices with \@@input, that's what I asked for. You
are right with the better solution but the original problem is much more
complicated and so this is not applicable.

Yours sincerely
Jobst

[Emily Rigdon]

You all made my day! This obscure rule about \multicolumn solved my problem exactly! I just rewrote my code so I could not be inputting lines that started with that line. I would have never figured this out by chance, and the debugging was already giving me a headache.
This may not have been the solution for the OP, but it sure was for me!
Thank you, thank you so much!