When to use trailing backslashes

Question

I am learning to use the puthesis document class. I have the following code:

\documentclass[iupuiece,thesis]{puthesis}

\begin{document}
\title{The Theory of Everything}
\campus{West Lafayette}
\author{Kit}
\maketitle

Hello World!

\end{document}

Take note of the \author line. That won't work. Out of the blue, I tried this one, and it works:

\author{Kit}\

The documentation here does not say anything about the trailing \. Is this some consistency issue with LaTeX syntax?

“Won’t work” is a very vague description: There should be no need for a backslash in this place. A concept “trailing backslash” doesn’t exist at all in LaTeX. — Konrad Rudolph, Sep 12 '10 at 14:17

score 21 · Accepted Answer · answered Sep 12 '10 at 16:41

21

A look in puthesis.cls shows that \author expects 2 arguments in this class:

\renewcommand*{\author}[2]{%
  \renewcommand*{\@@TitleAuthor}{#1}%
  \renewcommand*{\@@AbstractAuthor}{#2}%
}

So naturally everything explodes if this second argument is \maketitle.

answered Sep 12 '10 at 16:41

Ulrike Fischer

327,261

5

Two arguments to \author is just a bad UI design. I wish all class writers would listen to Boris Veytsman – Aditya Sep 15 '10 at 04:47

score 3 · Answer 2 · edited Apr 13 '17 at 12:34

As Konrad Rudolph points out, there is no such thing as a trailing backslash. (With the usual category codes,) A backslash is an escape character, and must be escaping something. In this case, it's escaping the following line break, which, if I remember correctly, is usually interpreted to mean the same as an escaped space, which, again if I remember correctly, is used to tell TeX that you want exactly one space where it might otherwise put 0 or more than 1:

Mr.\ Not-a-sentence
$bad\ way\ to\ put\ text\ in\ math\ mode$

(UPDATE: Probably a better example is the traditional use to prevent space-swallowing after a macro, as in \TeX\ is fascinating.) As Ulrike points out above, your original document attempts to pass the macro \maketitle as the second argument to \author, which breaks somewhere down the line (presumably when \@@AbstractAuthor is used); whereas the fixed document instead passes the macro \<par> as the second argument, which'll probably compile, but will put a space everywhere the abstract-author's name might be expected.

Assuming nothing has changed the \endlinechar, the second argument being passed (what you called \<par>) is \^^M. — TH., Sep 12 '10 at 23:11
TH., thanks! I actually discovered this shortly after posting by reading another one of your comments (which I can no longer find). Am I correct that ^^M by default (say, in Plain TeX) has the same effect as \ ? — LSpice, Sep 13 '10 at 05:11
@L Spice: Yes, that is correct; see p. 8 of the TeXbook, or search for "\def^^M" in plain.tex. — SamB, Dec 18 '10 at 22:12

When to use trailing backslashes

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