why You can't use `blank space ' after \the

Question

If I define

\newcount\punkt
\def\newpt{\the\punkt\space\advance\punkt by 1}

everything runs fine; but if I do

\newcounter{punkt}
\newcommand\newpt{\the\punkt\space\stepcounter{\punkt}}

I get

You can't use `blank space  ' after \the.

Why?

David Carlisle · Answer 1 · 2023-02-22T20:56:34.850

6

The code you posted, if used, generates a different error to the one you show.

\documentclass{article}
\newcounter{punkt}
\newcommand\newpt{\the\punkt\stepcounter{\punkt}}
\begin{document}
\newpt
\end{document}

! Undefined control sequence.
\newpt ->\the \punkt 
                     \stepcounter {\punkt }
l.9 \newpt
?

The latex command \newcounter does not define \punkt, you can use \thepunkt to get the print form.

\documentclass{article}
\newcounter{punkt}
\newcommand\newpt{\thepunkt\stepcounter{punkt}}
\begin{document}
\newpt
\newpt
\end{document}

You can generate the error shown using a construct such as

\documentclass{article}
\edef\x{\noexpand\the\space}\x
\begin{document}
\end{document}

! You can't use `blank space  ' after \the.
\x ->\the
l.3 \edef\x{\noexpand\the\space}\x
?

edited Feb 22 '23 at 20:56

answered Feb 22 '23 at 20:32

David Carlisle

757,742

FWIW, \newcommand\newpt{\the\punkt\space\stepcounter{\punkt}} does give the claimed error in Overleaf as the second error of six. – Teepeemm Feb 22 '23 at 20:45
1

@Teepeemm if you are brave enough to scroll past an error random unexpected behaviour should be expected:-) – David Carlisle Feb 22 '23 at 20:47
I run LaTeX in nonstopmode; the first exclamation mark was the one I reported, not the previous error. – jarnosc Feb 22 '23 at 21:47
@jarnosz as you did not post any code that gives an error I can't really comment. – David Carlisle Feb 22 '23 at 22:57
I was just trying to say that I ignored (very much like my LaTeX run) the first error, and flagged only the second... – jarnosc Feb 23 '23 at 20:56
1

@jarnosz I read your comment as saying the opposite, but always with TeX ignore all errors after the first, if you scroll past an error tex's "recovery", as here, will generate multiple spurious errors. – David Carlisle Feb 23 '23 at 21:02
wilco, and out! – jarnosc Feb 23 '23 at 21:06

score 5 · Accepted Answer · edited Feb 24 '23 at 19:14

The analog to Plain's \the\punkt in LaTeX would be

\the\csname c@punkt\endcsname

because when processing \newcounter{punkt} LaTeX does

\newcount\c@punct

Note the big difference: after \newcount (which is borrowed from plain TeX) there should be a control sequence name, whereas the argument to \newcounter is a string of characters that will be used to build different control sequences, namely

\c@punkt
\thepunkt
\p@punkt

The first one is the name of the allocated count register, the second one is the macro for the representation of the counter's value (by default \arabic{punkt}) and the last one is the “prefix” when processing a \label linked to this counter (see source2e for details). In particular, \newcounter{punkt} does not define \punkt.

So with \newcounter{punkt} and \the\punkt you get an error about an undefined control sequence (unless \punkt is independently defined) and if you press return at the error message, or if TeX is run in “nonstop” mode by a front-end, TeX ignores the undefined control sequence and proceeds to apply \the to the next token; since \space is expandable, TeX expands it and tries to apply \the to the resulting token list, but \the<space token> is illegal.

Always look at the first error message. And use \thepunkt instead.

therefore: \thepunkt instead of \the\punkt did fix the error. — jarnosc, Feb 22 '23 at 21:48

why You can't use `blank space ' after \the

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