Using \c{e} and other special characters in .bib files with pdflatex+biblatex+biber: How to avoid Package inputenc Error?

Question

I use Mendeley to manage my bibliography and have it automatically update .bib files. Unfortunately, this often leads to the "Package inputenc Error" when compiling.

I narrowed my problem down to this MWE (well non-working, but working with removal of \c{e} in .bib):

special.tex :

\documentclass{report}
\usepackage[T1]{fontenc} % necessary for "old text encoding" apparently (like for \k{a} (ogonek used in Polish))
\usepackage[utf8]{inputenc}
\usepackage[backend=biber]{biblatex}

\addbibresource{special.bib}

\begin{document}
  text:

  \c{c}
  \k{e}
  \k{a}
  \^{o}
  \c{e}

  \cite{foo2016}
  \printbibliography
\end{document}

special.bib :

@article{foo2016,
title = {{title}},
author = {
  \c{c}
  \k{e}
  \k{a}
  \^{o}
  \c{e}
},
}

problematic characters:
{\c{e}}

I compile with:

pdflatex special.tex
biber special
pdflatex special.tex

When \c{e} is removed from the bib entry, compilation works, despite the same character being present in the .tex file and rendering without issues in the main text.

While I could probably just use \k{e} here, which works, this is only one of many entries, which regularly get messed up whenever I do a DOI lookup in Mendeley or similar. I would prefer not to worry about encoding issues at all if possible.

Versions:

• biber: v1.9
• pdflatex: pdfTeX 3.14159265-2.6-1.40.15 (TeX Live 2014/Debian)
• biblatex: v2.9a

(but I had the same issue on ubuntu 16.04 with more recent packages, although I cannot test there at the moment)

edit: Here is the full entry as generated by DOI lookup in Mendeley (I created a new entry to make sure it's not my own fault):

@article{new_test_entry,
author = {Reithmaier, J. P. and S{\c{e}}k, G. and L{\"{o}}ffler, A. and Hofmann, C. and Kuhn, S. and Reitzenstein, S. and Keldysh, L. V. and Kulakovskii, V. D. and Reinecke, T. L. and Forchel, A.},
doi = {10.1038/nature02969},
issn = {0028-0836},
journal = {Nature},
mendeley-groups = {Personal},
month = {nov},
number = {7014},
pages = {197--200},
title = {{Strong coupling in a single quantum dot–semiconductor microcavity system}},
url = {http://www.nature.com/doifinder/10.1038/nature02969},
volume = {432},
year = {2004}
}

Answer 1

biber will (not always but quite often) convert an accent command to the decomposed unicode representation "char + combining accent". But pdflatex can't handle combining accents. So as long as you are using pdflatex you must avoid that this happens.

To do this you can

• tell biber not to output everything in utf8 with --output-safechars and similar options
• or input in the bib directly the correct utf8 char, in your case LATIN SMALL LETTER E WITH CEDILLA' (U+0229) as ȩ. Sometimes you will have to add definitions for such chars.
• or if you want to use commands in the bib, fool biber by using a different name, e.g. \cedilla{e}, and in your document do \let\cedilla\c. But be aware that biber then no longer can recognize the intended glyph and so sorting can be wrong.

Edit:

Actually this here is one of the case where biber doesn't output a combining accent. The problem is simply that U+0229 is not declared. One only needs to add \DeclareUnicodeCharacter{0229}{\c{e}} and \c{e} in the bib will work.

To demonstrate the last two advice. This bib-file

@article{foo2016,
title = {{title}},
author = {
  \c{c}
  \k{e}
  \k{a}
  \^{o}
  \cedilla{e}
  ȩ
},
}

with this document

\documentclass{report}
\usepackage[T1]{fontenc} % necessary for "old text encoding" apparently (like for \k{a} (ogonek used in Polish))
\usepackage[utf8]{inputenc}
\usepackage[backend=biber]{biblatex}

\addbibresource{special.bib}

\newcommand\cedilla{}
\let\cedilla\c
\DeclareUnicodeCharacter{0229}{\c{e}}
\begin{document}
  \cite{foo2016}
  \printbibliography
\end{document}

will give this result

Answer 2

I'd like to point out it all works fine with xelatex, as long as the font contains all characters. It seems lmodern doesn't have the ȩ. Demonstration with lmodern (the default with xelatex, and erewhon (an extension of Adobe Utopia):

\documentclass{report}
\usepackage{fontspec}
\setmainfont{erewhon}
\usepackage{csquotes} \usepackage[backend=biber]{biblatex}

\addbibresource{special.bib}

\begin{document}
text:

ç
ę
ą
ô
ȩ

\cite{foo2016}
\printbibliography
\end{document} 

Bib file:

@article{foo2016, title = {{title}}, author = {
  ç
  ę\k{e}
  ą\k{a}
  ô
  ȩ\c{e}
}, }

Result with lmodern:

Result with erewhon: