Convert integer to its ASCII character

Question

In the ASCII table, …

! (exclamation mark) is also a printable character and its decimal representation is 33
a (latin small letter a) is a printable character and its decimal representation is 97
} (right curly bracket) is also a printable cahracter and its decimal representation is 125

I want to know if there's a macro in LaTeX that converts a decimal representation to its ASCII character.

\symbol{...} returns a for 97 and ! for 33. I thought that \symbol{...} accomplished what I am looking for, but it returns ˝ (double acute accent) for 125.

\documentclass{article}
\begin{document}
\symbol{33} % exclamation mark
\symbol{97} % latin small letter a
\symbol{125} % it should return "right curly bracket", but it returns ˝ (double acute accent)
\end{document}

My question is: In the context of LaTeX, is there a built-in macro to convert an integer (i.e. decimal representation) to its ASCII character? The macro should work for any printable character in ASCII (i.e. between the range 32 to 126.)

I found this question which is similar to my question, but it was conflated with the definition of "extended ascii table".

It can't work if the symbol is not available in the current font encoding. That would be rare for these characters, but far from impossible. — cfr, Mar 27 '24 at 06:50

score 10 · Answer 1 · answered Mar 27 '24 at 06:19

The TeXbook says

To get access to any character whatsoever, you can type

\char⟨number⟩

where ⟨number⟩ is any number from 0 to 255 (optionally followed by a space); you will get the corresponding character from the current font.

The default font is cmr10, in which the font character in position 125 ('175 in octal notation) is ̋ . That's why \char125 and \symbol{125} return ̋ instead of right curly brace.

However, the cmtt10 font is consistent with ASCII table (To confirm this, have a look at page 429 of the TeXbook). So, in order to have \char125 produce the right curly brace, you can choose to use cmtt10 font:

\documentclass{article}
\begin{document}
\texttt{\char33\char37\char97\char125\symbol{125}}
\end{document}

Another method is using T1 font encoding, i.e., adding

\usepackage[T1]{fontenc}

in the preamble.

\documentclass{article}
\usepackage[T1]{fontenc}
\begin{document}
\char33\char37\char97\char125\symbol{125}
\end{document}

score 5 · Answer 2 · answered Mar 27 '24 at 06:38

The TeX primitive \char number creates a character with given code number. The TeX primitive \Uchar number creates a token with given code number. The second one is implemented only in XeTeX and LuaTeX. The difference is: \char number works after tokenization (in XeTeX or LuaTeX, the Unicode is accepted) and it is not expandable, \Uchar number returns a Unicode character: token of category 12 and it is expandable.

score 2 · Answer 3 · answered Mar 27 '24 at 12:02

As wipet says, at the primitive level, classical engines do not offer a way to generate a character by expansion. However, this can be done using macros: in expl3 there is \char_generate:nn for this purpose, or for more general codepoints (full Unicode coverage), \codepoint_generate:nn. We might therefore do

\ExplSyntaxOn
\cs_new:Npn \mysymbol #1 { \codepoint_generate:nn {#1} { 12 } }
\ExplSyntaxOff

to create a command \mysymbol that makes 'other' characters across the Unicode range by expansion.

Note that as Stephen says, this doesn't mean that a symbol will be printable directly.

Convert integer to its ASCII character

3 Answers3