Missing character: There is no ? in font cmr12!

Question

I'm not quite sure how to diagnose this issue. This is what I see in my log file. However, there are no "?" symbols in my work.

FWIW, Here's my preamble:

\documentclass[12pt]{article}
\title{Title}
\author{Author}
\date {February 2012}
\usepackage{wallpaper}
\usepackage{fullpage}
\usepackage{hyperref}
\hypersetup{colorlinks=false,pdfborder={0 0 0},}
\SweaveOpts{concordance=TRUE,echo=FALSE,warnings=FALSE,message=FALSE}

\begin{document}

\ThisULCornerWallPaper{1}{documenthead.jpg}
\LLCornerWallPaper{1}{footer.jpg}

% TITLEPAGE

\begin{titlepage}
\maketitle
\end{titlepage}

\tableofcontents{}
\clearpage
...
\end{document}

Answer 1

This error message is low-level TeX output which shows up if you are typesetting material in a font (external name "cmr12" in your example) and you are trying to typeset a glyph that is not in the font. The ? is not a real question mark it stands for a character that is unknown.

When you are typesetting a word, say, "aha" then deep down this is all translated to glyph positions in a font. For example, the "a" in most encodings represents the font position octal:141 and "h" is octal:150. Whatever glyphs are in these positions in the current font will be typeset (which may not look remotely like "a" or "h").

Now, the font in question has only the first 128 slots filled (it is a 7 bit font) and what happened most likely is that your document contains diacritical characters which in most encodings map to positions with number in the range from 128-255. And if these slots do not exist you get the error message.

Possible resolutions:

• Use only 7 bit input, e.g., \'a instead of straight á
• Use the "correct" input encoding for your document, e.g. \usepackage[latin1]{inputenc} if the document is written in the 8 bit Latin1 coding, or \usepackage[utf8]{inputenc} if it is in UTF8. Chosing the correct input encoding results in characters like á are automatically translated back internally by LaTeX to \'a.

In either case it is sensible to add \usepackage[T1]{fontenc} in your preamble so that 8 bit fonts are used as these will result in better quality if accented characters are used. If an 8 bit font encoding is used then commands like \'a are no longer constructing the diacritical characts but instead select the real glyph in the font.

Answer 2

It is easy to generate such messages:

\documentclass{article}
\begin{document}
 äö¿
\end{document}

But to be able to know what in your document is the source of the message a complete example is needed.