\endinput: what is it for?

Question

I am working on a big document and I am using the \include command to put chapters one after the other. On the internet I came to know about the existence of the \endinput command. However I do not understand how to use it. My questions:

1. If I have a LaTeX chapter file named chapter1.tex, should I place the \endinput command on the last line in the file chapter1.tex?

2. If yes for Question 1, then should I do the same for every other chapters that I have?

I have never used \endinput before and everything has worked fine so far.

Answer 1

No, you don't need it.

\endinput is used for terminating the input process in the middle of a file. A \endinput at the end of a file is useless (and harmless).

Some ones like to use \endinput to show the end of file explicitly. IMHO, it make no sence.

Answer 2

Here's a case where \endinput might be useful. Suppose I'm writing a textbook and that each chapter ends with problems followed by their solutions. I want to build two separate editions: one for students, without solutions, one for teachers, with solutions.

I can define a conditional, say \ifstudent, and prepare my chapters as

<text>
\section*{Problems}
<problems>

\ifstudents\endinput\fi

\section*{Solutions}
<solutions>

Now it suffices to switch \studentfalse (for the teachers' edition) and \studenttrue (for the students' edition).

An important feature of \endinput is that TeX continues to read to the end of the line where \endinput appears (when it is expanded), so something can follow it and be read nonetheless. The following would be equivalent

\ifstudents
  \expandafter\endinput
\fi

Forgetting the \expandafter would cause an "incomplete conditional" error message.

Answer 3

if one has the documentation of a package inside the package itself he can use \endinput before the documentation text starts, e.g. package url

Answer 4

if you are sending a multi-file manuscript to a publisher that uses a different production platform than you do, \endinput at the end of chapter files to be \included will serve to avoid possible problems with different end-of-line characters or addition of spurious garbage at the end of a file to fill out a fixed-length block. these conditions are rare, but quite nasty when they do occur.

Answer 5

Beside allowing comments at the end of the file \endinput (or any other command) can also be useful to swallow spaces introduced by the end-of-file. E.g. if your input file contains abc x\input{file}y will give xabc y. If the input file is abc\endinput you will get xabcy.

Answer 6

The \include macro uses the \input macro internally to read the given file. The \endinput macro simply ends the input of this file, i.e. allows you to have everything afterwards ignored and return to the parent file immediately. As Herbert already stated this is useful for package or similar files which have its documentation in them and place them just after \endinput so is isn't interpreted it as LaTeX code.

For own chapters inside \included file \endinput can be useful if you want to temporary ignore a trailing portion of this chapter. Together with \includeonly it allows you to produce a partial PDF just holding e.g. the first section of a chapter. This can be very useful in the writing phase e.g. if you are supposed to sent such a part of your document to another person for review.

AFAIK the guide for LaTeX package authors states to end class and package files with an explicit \endinput. I personally find it good programming style. I also remember hearing about some tricks which require an explicit \endinput in the file they process, which I think is then temporary redefined.

In summary, you don't have to worry about \endinput. It's totally fine if you don't use it at all.