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

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 2

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}}.