Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!usc!julius.cs.uiuc.edu!ux1.cso.uiuc.edu!csrd.uiuc.edu!s41.csrd.uiuc.edu!eijkhout
From: eijkhout@s41.csrd.uiuc.edu (Victor Eijkhout)
Newsgroups: comp.text.tex
Subject: Re: Problem using \write
Message-ID: <1990Dec13.164542.21155@csrd.uiuc.edu>
Date: 13 Dec 90 16:45:42 GMT
References: <1990Dec13.090011.15883@ariel.unm.edu>
Sender: news@csrd.uiuc.edu (news)
Organization: UIUC Center for Supercomputing Research and Development
Lines: 28

wester@ghostwheel.unm.edu (Michael Wester) writes:

>\def\qqq{\length{argument}}   % try out an example
>\qqq                          % this causes an 8 to be written in the DVI file
>\immediate\write16\qqq        % however, this causes an error

>[...]  I presume the \write causes
>the same sort of expansion as \edef.  

Correct. And to add to your problems: the length macro uses
not only expansion, but also assignments, which are not
expandable.

You can view your results interactively but having the \write
*inside* the macro you are testing. Of course this is not what
you want.

This may be a silly solution, but I think it works:

\setbox0\hbox{\qqq}
\tracingonline=1
\showbox0

This shows you what's in box0 (without the \tracingonline you
get this only in your log file), in particular
the characters that have been typeset in it.

Victor.