Umlaut Latex Bibliography Cite

LaTeX forum ⇒ BibTeX, biblatex and biber ⇒ natbib undefined citationsTopic is solved

Information and discussion about BiBTeX - the bibliography tool for LaTeX documents.

Joined: Sat Jul 04, 2009 7:20 pm

natbib undefined citations

Postby pricejn2 » Tue Jul 07, 2009 2:04 am

I'm having all sorts of trouble with my BiBTeX. The main problem of course is that citations are not being properly referenced in the final document.

I'm working in Windows and when I try to build my .tex document to DVI I get multiple errors akin to this:

Package natbib Warning: Citation `number1' on page 1 undefined on input line 76.
Package natbib Warning: Empty `thebibliography' environment on input line 5.
Package natbib Warning: There were undefined citations.

A couple of notes:
(1) my .bib file has a ä character and I was getting encoding issues...current encoding is ISO-8859-1 (Latin-1) to resolve character conflicts

(2) if i run bibtex myfile from command prompt I get a I couldn't open database file references.bib

(3) of course i'm not using \begin{thebibliography} but my .bbl file looks like this:

(4) line 5 has

Trying to avoid manual entry for thesis...any help GREATLY appreciated.

Also: probably unrelated, but if I comment out \usepackage{pdfpages} in the preamble, I get: missing number treated as zero, all illegal unit of measure, and undefined control sequence errors for each *.eps figure. I don't get it...
Joined: Tue Mar 25, 2008 5:02 pm
Location: Columbia, Missouri, USA

Postby kaiserkarl13 » Tue Jul 14, 2009 10:06 pm

This could be a number of things, both in the BibTeX file (.bib) and in the LaTeX file (.tex).

First, make sure your database is in a location in which BibTeX can find it (the current directory works well). This should clear up the "I couldn't open database file references.bib" message. The .aux file and .bib file must both be in BibTeX's search path (which is often different than LaTeX's search path; move it to the current directory to make sure).

Second, I recommend removing any non-ASCII files from your BibTeX database. For example, an entry with the name Koeln in it (spelled with the umlaut instead of the oe) might look like:

Once that's fixed, see if you've fixed your problems.
Joined: Tue Apr 13, 2010 5:18 pm

Postby kahlan » Wed Apr 14, 2010 10:08 am

Dear kaiserkarl13!

I have the same prob here. Looks to me that everything is according to your advices: .aux file and .bib file are in the same folder.

I am using Latex on Linux.
Error message looks like this:

[PDFLaTex] .tex => .pdf (pdflatex)
./.bbl:8: Empty 'thebibliography' environment on input line 8.

[BibTex] .aux => .bbl (bibtex)
[BibTex] finished with exit code 2

Thanks for your help beforehand.

Joined: Wed Jul 11, 2007 11:45 pm
Location: Colombia

Postby gmedina » Wed Apr 14, 2010 3:46 pm

kahlan wrote:[PDFLaTex] .tex => .pdf (pdflatex)
./.bbl:8: Empty 'thebibliography' environment on input line 8.

[BibTex] .aux => .bbl (bibtex)
[BibTex] finished with exit code 2

The message suggests that you are not using \cite commands in your document; try adding \nocite{*} (this command will include all the entries of the .bib file in the references section, even if not explicitly cited) in the body of your document.

If that was not the problem, we will need to see some of the actual code that you are using (a minimal, compilable version including only the code relevant to the problem mentioned).
Joined: Mon Nov 08, 2010 4:29 am

Postby herlimenezes » Mon Nov 08, 2010 4:36 am


I got the same problem. My .bib files are in folder: /home/UserName/Area de Trabalho/Documentos/ReferenciasArtigos.bib
I put this path into command \bibliography{'/home/UserName/Area de Trabalho/Documentos/ReferenciasArtigos.bib'}. I have used quotes because of the blank spaces at Area de Trabalho folder. Got no positive results, so I moved ReferenciasArtigos.bib to the project folder (I am using Kile), nothing happens. What can I do?
BTW, I am using multiple documents im my dissertation.

Does anybody can help me?

One more thing: I am using JabRef, so that it automatically inserts citation into latex text. Appararently it works fine (when I use LyX processor...)

Thanks in advance.
Joined: Sun Dec 19, 2010 4:21 pm

Postby john_s » Sun Dec 19, 2010 4:32 pm

I've been having similar problems with natbib. There was an obscure message at the end of the undefined citations suggesting that there was an inappropriate ampersand (&) in the .bbl file.

Turned out that some citations retrieved from Medline put a URL field into the .bib file, and these contain the '&' which apparently confuses natbib. Not clear whether this is sometimes used, but I just deleted these by hand and then it all worked.
Joined: Wed Feb 23, 2011 6:16 pm

Postby elstefano » Wed Feb 23, 2011 6:23 pm

Hey People,
I just had the same problem as you and, for me, the solution was very easy: I included my .bib file as follows:

I was getting used to write everything with ending, coz I got some problems earlier on when including graphics. But here, it can cause an error.

Probably this is of help for some of you.


  1. \bibliographystyle{elsarticle-harv}
  2. \bibliography{thesis_ref.bib}
  3. ... whereas the ending .bib must not be written down:
  4. \bibliographystyle{elsarticle-harv}
  5. \bibliography{thesis_ref}
Last edited by cgnieder on Tue Feb 19, 2013 9:25 pm, edited 1 time in total.
Reason:added code markup
Joined: Thu Jul 05, 2012 4:15 pm

Postby DVa » Thu Jul 05, 2012 4:34 pm


My solution of the Bibtex error compilation is different.

I was using latex on Windows through MikTeX. No problem. I then moved to latex linux using texlive2009 and had the "[BibTex] finished with exit code 2" error message each time I compiled Bibtex. The former posts would not solve my problem in my case.

The error occured because I had a duplicate reference (with same name) in my .bib file. Apparently, with MikTeK, Bibtex can overpass this duplication but bibtex with texlive can't.

Hope this helps.
Joined: Tue Feb 19, 2013 12:35 pm

Postby balajiSankar » Tue Feb 19, 2013 12:40 pm


I had the same problem . This is what solved it.
I was having entries like the one below:

This was giving the undefined citations error. When i changed them to

it worked and all were happy
  1. @ARTICLE{gasTurbineCombustor_GeneralMotors_AIAA}
  2. AUTHOR = {N.K.Rizk , H.C.Mongia},
  3. TITLE = {Gas Turbine combustor performance evaluation},
  4. JOURNAL = {29^{th } Aerospace sciences meeting},
  1. @ARTICLE{gasTurbineCombustor_GeneralMotors_AIAA}
  2. AUTHOR = {"N.K.Rizk , H.C.Mongia"},
  3. TITLE = {"Gas Turbine combustor performance evaluation"},
  4. YEAR = {"1991"},
  5. JOURNAL = {"29^{th } Aerospace sciences meeting"},
  6. NUMBER = {"AIAA-91-0640"},
Last edited by cgnieder on Tue Feb 19, 2013 9:25 pm, edited 1 time in total.
Reason:added code markup

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In this chapter we will tackle matters related to input encoding, typesetting diacritics and special characters.

In the following document, we will refer to special characters for all symbols other than the lowercase letters a–z, uppercase letters A-Z, figures 0–9, and English punctuation marks.

Some languages usually need a dedicated input system to ease document writing. This is the case for Arabic, Chinese, Japanese, Korean and others. This specific matter will be tackled in Internationalization.

The rules for producing characters with diacritical marks, such as accents, differ somewhat depending whether you are in text mode, math mode, or the tabbing environment.

Input encoding[edit]

TeX uses ASCII by default. But 128 characters is not enough to support non-english languages. TeX has its own way to do that with commands for every diacritical marking (see Escaped codes). But if we want accents and other special characters to appear directly in the source file, we have to tell TeX that we want to use a different encoding.

There are several encodings available to LaTeX:

  • ASCII: the default. Only bare english characters are supported in the source file.
  • ISO-8859-1 (a.k.a. Latin 1): 8-bits encoding. It supports most characters for latin languages, but that's it.
  • UTF-8: a Unicode multi-byte encoding. Supports the complete Unicode specification.
  • Others...

In the following we will assume you want to use UTF-8.

There are some important steps to specify encoding.

  • Make sure your text editor decodes the file in UTF-8.
  • Make sure it saves your file in UTF-8. Most text editors do not make the distinction, but some do, such as Notepad++.
  • If you are working in a terminal, make sure it is set to support UTF-8 input and output. Some old Unix terminals may not support UTF-8. PuTTY is not set to use UTF-8 by default, you have to configure it.
  • Tell LaTeX that the source file is UTF-8 encoded.

inputenc[1] package tells LaTeX what the text encoding format of your files is.

The inputenc package allows as well the user to change the encoding within the document by means of the command .

\usepackage[utf8]{inputenc}% ...% In this area% The UTF-8 encoding is specified.% ...\inputencoding{latin1}% ...% Here the text encoding is specified as ISO Latin-1.% ...\inputencoding{utf8}% Back to the UTF-8 encoding.% ...

Extending the support[edit]

The LaTeX support of UTF-8 is fairly specific: it includes only a limited range of unicode input characters. It only defines those symbols that are known to be available with the current font encoding. You might encounter a situation where using UTF-8 might result in error:

! Package inputenc Error: Unicode char \u8:ũ not set up for use with LaTeX.

This is due to the utf8 definition not necessarily having a mapping of all the character glyphs you are able to enter on your keyboard. Such characters are for example

ŷ Ŷ ũ Ũ ẽ Ẽ ĩ Ĩ

In such case, you may try need to use the utf8x option to define more character combinations. utf8x is not officially supported, but can be viable in some cases. However it might break up compatibility with some packages like csquotes.

Another possiblity is to stick with utf8 and to define the characters yourself. This is easy:

\DeclareUnicodeCharacter{'codepoint'}{'TeX sequence'}

where codepoint is the unicode codepoint of the desired character. TeX sequence is what to print when the character matching the codepoint is met. You may find codepoints on this site. Codepoints are easy to find on the web. Example:


Now inputting 'ŷ' will effectively print 'ŷ'.

Escaped codes[edit]

In addition to direct UTF-8 input, LaTeX supports the composition of special characters. This is convenient if your keyboard lacks some desired accents and other diacritics.

The following accents may be placed on letters. Although 'o' letter is used in most of the examples, the accents may be placed on any letter. Accents may even be placed above a "missing" letter; for example, produces a tilde over a blank space.

The following commands may be used only in paragraph (default) or LR (left-right) mode.

LaTeX commandSampleDescription
ògrave accent
óacute accent
öumlaut, trema or dieresis
őlong Hungarian umlaut (double acute)
łbarred l (l with stroke)
ōmacron accent (a bar over the letter)
obar under the letter
ȯdot over the letter
dot under the letter
åring over the letter (for å there is also the special command )
ŏbreve over the letter
šcaron/háček ("v") over the letter
o͡o"tie" (inverted u) over the two letters
øslashed o (o with stroke)

To place a diacritic on top of an i or a j, its dot has to be removed. The dotless version of these letters is accomplished by typing and . For example:

  • should be used for i circumflex 'î';
  • should be used for i umlaut 'ï'.

If a document is to be written completely in a language that requires particular diacritics several times, then using the right configuration allows those characters to be written directly in the document. For example, to achieve easier coding of umlauts, the babel package can be configured as . This provides the short hand for . This is very useful if one needs to use some text accents in a label, since no backslash will be accepted otherwise.

More information regarding language configuration can be found in the Internationalization section.

Less than < and greater than >[edit]

The two symbols '<' and '>' are actually ASCII characters, but you may have noticed that they will print '¡' and '¿' respectively. This is a font encoding issue. If you want them to print their real symbol, you will have to use another font encoding such as T1, loaded with the fontenc package. See Fonts for more details on font encoding.

Alternatively, they can be printed with dedicated commands:

Euro currency symbol[edit]

When writing about money these days, you need the euro sign. The textcomp package features a command which gives you the euro symbol as supplied by your current text font. Depending on your chosen font this may be quite far from the official symbol.

An official version of the euro symbol is provided by eurosym. Load it in the preamble (optionally with the official option):


then you can insert it with the command. Finally, if you want a euro symbol that matches with the current font style (e.g., bold, italics, etc.) you can use a different option:


again you can insert the euro symbol with .

Alternatively you can use the marvosym package which also provides the official euro symbol.

\usepackage{marvosym}% ...\EUR{}

Now that you have succeeded in printing a euro sign, you may want the '€' on your keyboard to actually print the euro sign as above. There is a simple method to do that. You must make sure you are using UTF-8 encoding along with a working or command.

\DeclareUnicodeCharacter{20AC}{\euro{}}% or\DeclareUnicodeCharacter{20AC}{\EUR{}}

Complete example:


Degree symbol for temperature and math[edit]

The easiest way to print temperature and angle values is to use the command from the siunitx package, which works both in text and math mode:

\usepackage{amsmath}\usepackage{siunitx}%... A $\SI{45}{\degree}$ angle. It is \SI{17}{\degreeCelsius} outside.

For more information, see the documentation of the siunitx package.

A common mistake is to use the command. It will not print the correct character (though will). Use the textcomp package instead, which provides a command.

\usepackage{textcomp}%... A $45$\textdegree angle.

For temperature, you can use the same command or opt for the gensymb package and write

\usepackage{gensymb}\usepackage{textcomp}%... 17\,\celsius% best (with textcomp)

Some keyboard layouts feature the degree symbol, you can use it directly if you are using UTF-8 and textcomp. For better results (font quality) we recommend the use of an appropriate font, like lmodern:

\usepackage[utf8]{inputenc}\usepackage{lmodern}\usepackage{textcomp}% ... 17\,°C 17\,℃ % best

Other symbols[edit]

LaTeX has many symbols at its disposal. The majority of them are within the mathematical domain, and later chapters will cover how to get access to them. For the more common text symbols, use the following commands:

Not mentioned in above table, tilde (~) is used in LaTeX code to produce non-breakable space. To get printed tilde sign, either write or . And a visible space ␣ can be created with .

For some more interesting symbols, the Postscript ZapfDingbats font is available thanks to the pifont package. Add the declaration to your preamble: . Next, the command , will print the specified symbol. Here is a table of the available symbols:


In special environments[edit]

Math mode[edit]

Several of the above and some similar accents can also be produced in math mode. The following commands may be used only in math mode.

When applying accents to letters and , you can use and to keep the dots from interfering with the accents:

Tabbing environment[edit]

Some of the accent marks used in running text have other uses in the tabbing environment. In that case they can be created with the following command:

  • for an acute accent
  • for a grave accent
  • for a macron accent

Unicode keyboard input[edit]

Some operating systems provide a keyboard combination to input any Unicode code point, the so-called unicode compose key.

Many X applications (*BSD and GNU/Linux) support the combination. A 'u' symbol should appear. Type the code point and press or to actually print the character. Example:

<Ctrl+Shift+u> 20AC <space>

will print the euro character.

Desktop environments like GNOME and KDE may feature a customizable compose key for more memorizable sequences.

Xorg features advanced keyboard layouts with variants that let you enter a lot of characters easily with combination using the aprioriate modifier, like . It highly depends on the selected layout+variant, so we suggest you to play a bit with your keyboard, preceeding every key and dead key with the modifier.

In Windows, you can hold and type a to get a desired character. For example,

<Alt> + 0252

will print the German letter ü.

External links[edit]

Notes and References[edit]

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