Non-breaking space in \citet using natbib?

Question

When adding citations in the body of a document I'm used to write

... in some interesting paper~\cite{interesting}.

So that (if I'm using numbered references) the word “paper” and the citation number stick together and do not accidentally end up in two different lines.

It seems, however, that the \citet command from natbib (which should produce something like “Authors [4]”), does not use a ~ between the names of the authors and the citation number so that, on a few rare occasions, I end up with something like

                                                  ... Authors
[4].

Which is annoying. Is there an easy way to make natbib use a non-breaking space there?

Answer 1

lockstep and Stefan Kottwitz suggest redefining \NAT@spacechar. That may have worked at one time, but I find that it no longer works now, seven years later, using natbib 2010/09/13 8.31b (PWD, AO) from TeXLive 2016. A comment from @penelope also mentions that this approach was no longer working as of mid-2014.

The following strategy does work for me as of now. Add the following to your document preamble somewhere after \usepackage{natbib}:

\bibpunct{\nolinebreak{}[}{]}{,}{n}{}{,}

The key piece of this is the \nolinebreak{}[, which discourages LaTeX from breaking a line before the [ that starts a group of bracketed citation numbers. The remaining arguments to \bibpunct merely replicate the standard punctuation for bracketed, numbered citations.

Note that the {} immediately after \nolinebreak is not really an empty argument to \nolinebreak. Rather, it simply prevents \nolinebreak from mistaking the following [ for the start of an optional argument. That being said, \nolinebreak does accept an optional argument that determines how strongly a break should be discouraged. So you could instead use something like \bibpunct{\nolinebreak[0][}{]}{,}{n}{}{,} to make the no-break directive merely a mild request, all the way up to \bibpunct{\nolinebreak[4][}{]}{,}{n}{}{,} for a strict demand. The latter is equivalent to the default treatment you get if you use the \bibpunct{\nolinebreak{}[}{]}{,}{n}{}{,} form I suggested initially.

Answer 2

Looks like \NAT@spacechar needs to be redefined:

\documentclass{article}

\usepackage[numbers]{natbib}

\makeatletter
% \def\NAT@spacechar{\ }% OLD
\def\NAT@spacechar{~}% NEW
\makeatother

\usepackage{filecontents}

\begin{filecontents}{\jobname.bib}
@misc{a01,
  author = {Author, A.},
  year = {2001},
  title = {Alpha},
}
\end{filecontents}

\begin{document}

Let's test if author and citation number end up in different lines: \citet{a01}.

\bibliographystyle{plainnat}
\bibliography{\jobname}

\end{document}

Answer 3

Since \NAT@spacechar is used, this redefinition prevents such breaks:

\makeatletter
\renewcommand*{\NAT@spacechar}{~}
\makeatother

This could affect also places where a break could be desired. Thus, an easy way for your rare occasions would be to use just \mbox around the citation:

... in the paper \mbox{\citet{interesting}}.

Answer 4

@JanJones answer worked for me too when using biblatex. I applied it as follows also fixing multicitedelim

\renewcommand*{\namelabeldelim}{\nobreakspace}
\renewcommand*{\multicitedelim}{\addcomma\nobreakspace}

Answer 5

Redefining namelabeldelim to use non-breaking space (\addnbspace) worked for me:

\DeclareDelimFormat{namelabeldelim}{\addnbspace}