# How to detect an empty unicode slot in a font?

Consider the below unicode table. Some slots are undefined by the Unicode Consortium and appear empty in the table (slot 7,8,15 &16 in second row). How can I detect these and replace the characters with a symbol?

Minimal:

\documentclass{article}
\usepackage{fontspec}
\newfontfamily\greek{Times New Roman}
\makeatletter
%puts the unicode label (removes last char and adds x)
\def\putunicode@label#1#2;{%
\def\reformat@unicode@string##1{%
\bgroup%
\ttfamily
U+%
\edef\z{}%
\expandafter\@tfor\expandafter\i\expandafter:\expandafter=#2;\do{%
\if\i;x\space
\else\z\fi%
\edef\z{\i}%
}%
\egroup
}%
\makebox[5em]{\reformat@unicode@string{#2}}%
}

\def\putchar@cx#1{%
\char\n$_{\the\r}$
}

\def\urow@cx#1{%
\parindent0pt%
\n=#1%
\r=1%
\expandafter\putunicode@label#1;%
\loop%
\ifnum\n<\numexpr#1+16%
\makebox[2.1em]{\expandafter\putchar@cx{#1}}%
\ifnum\r>16\r=1\relax\else\fi
\repeat
\par
}

\def\typeseturows@cx#1{%
\@for\next:=#1\do{%
\urow@cx\next\vskip3pt}}

\newcommand\unicodetable[2]{%
\par\leavevmode
\bgroup%
\parindent0pt%
\newcount\n%
\newcount\r%
\r=1%
\raggedright%
\@nameuse{#1}%
\r=1%
{\ttfamily\makebox[3.1em]{}}%
\loop%
\ifnum\r<17%
\makebox[2.1em]{\hfill\texttt{\the\r}\hfill}%
\repeat
\vskip3pt
\typeseturows@cx{#2}%
\egroup%
}

\makeatother

\begin{document}

\unicodetable{greek}{"1F00,"1F10,"1F20,"1F60}

\end{document}


Use \iffontchar:

\def\putchar@cx#1{%
\iffontchar\font\n
\char\n$_{\the\r}$%
\else
*%
\fi
}


The conditional \iffontchar\font<number> is true if a character is present in the slot <number>, false otherwise.

I've also removed a spurious space after \$, but there are other glitches in your code. I'll refer to line numbers in your original code.

1. Line 27 should be \parindent=0pt (no trailing %)

2. Line 32 should be \ifnum\n<\numexpr#1+16\relax

3. Lines 34 and 36 should be \advance\r by1 (no trailing %) or \advance\r by\@ne

4. Line 35 should be \ifnum\r>16 \r=1 \else\fi

5. Lines 50 and 51, that is \newcount\n and \newcount\r should be outside the definition of \unicodetable. Using \r is not really a good choice.

6. Lines 52 and 55 should be \r=1 (no trailing %)

7. Line 58 should be \ifnum\r<17 (no trailing %)

8. Line 60 should be \advance\r by1 (no trailing %)

The % characters I suggest to remove may cause untimely expansions. Allocating registers in the definition of a macro should be done only if the assigned names depend on the macro arguments: at any call of \unicodetable you'd be wasting two counter registers.

• @YiannisLazarides I noted other glitches. Besides them there are several redundant %, which are innocuous, though. – egreg Sep 21 '14 at 19:27
• Thanks once more. It is still buggy, I need to test it a bit more. – Yiannis Lazarides Sep 21 '14 at 19:55
• But this handles just characters not covered by the font which might or might not be assigned Unicode characters. – Khaled Hosny Sep 22 '14 at 8:06
• @KhaledHosny For the "unassigned slots" there's no primitive that I know of. Maybe a read only table with the status of a slot (unassigned/assigned in version x.y of Unicode) could be a solution. – egreg Sep 22 '14 at 8:59