{catcodes} is about "category codes" — an integer number from 0–15 associated to each of the 256 character codes. The category codes indicate the role of a character.

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406
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What do \makeatletter and \makeatother do?

Many LaTeX “hacks” begin with \makeatletter and end with \makeatother. What do these commands do?
45
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What are category codes?

Following on from this question, I'd like to ask a more general question: What are category codes, and what can I achieve by changing them?
12
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Removing a backslash from a character sequence

For indexing I wanted to write a macro \macroname that removes leading backslashes from macro names but leaves the names of environments untouched. That is \macroname{\relax} --> relax ...
20
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4answers
3k views

How to make a real backslash (escape) character?

I just want a good way to make a backslash character (or whatever character(s) any given format uses as escape characters), suitable to \write to a file or pass to a pdfTeX primitive. Let me ...
8
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2answers
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\makeatletter explained

I am using the following code in my beamer document to make the frame title's appear in the table of contents: \documentclass{beamer} \usetheme{default} \usepackage{bookmark} \usepackage{etoolbox} ...
15
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1answer
870 views

How to change the catcode in a macro

I want to change the catcode in a macro, but it seems it doesn't work. Can anyone help me? \def\A{\catcode`\|=0 |bf{test}} |bf{test} would not work as expect.
9
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993 views

Changing the catcode of _ in one command?

In the following code, I would like _ to be a simple letter. How can I achieve this ? % Source : http://forum.mathematex.net/latex-f6/forcer-le-retour-a-la-ligne-dans-texttt-t13246.html#p127511 ...
29
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5answers
3k views

Using indentation to automatically begin and end itemize environments

This is a question one might answer with "Why the hell would you want to do it?!", sort of an experiment. What I am looking for is a way to write lists with many levels of nestings (notes for school) ...
21
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4answers
4k views

Underscore in textmode vs mathmode

I use _ character often in text mode, so I changed category of underscore: \catcode\_=12, but that applies also to mathmode and now I'm unable to make subscripts with underscore in mathmode. Is there ...
12
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1answer
602 views

Catcodes of unicode characters with \usepackage[utf8]{inputenc}

I don't understand why this is generating an error message... \documentclass{article} \usepackage[utf8]{inputenc} \begin{document} \catcode`ẟ=\active \end{document} As the inputenc suggests, I'm ...
11
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2answers
785 views

“Activate” active characters in argument passed as macro

Let's say I have some macro (\iPrint in the MWE) that internally uses active characters to interpret its argument: \documentclass{article} \usepackage[utf8]{inputenc} \usepackage[T1]{fontenc} ...
17
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3answers
414 views

Can I convert a string to catcode 11?

In the TeX FAQ there's a way to test if the jobname is equal to something (comparing the jobname). The difficulty of the naïve test is that the contents of the \jobname primitive are catcode 12 so to ...
5
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196 views

Changing catcode for commercial at (@) inside a macro to get it matched in pattern.

This question is related to TikZ: pgfutil-common: pgfutil@in@ - how does it work? and is a result of coping with that problem. I've already read How to change #catcode in a macro, but it didn't help ...
25
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2answers
885 views

What is the differences between mathcode and catcode and how can I use mathcode?

The command \catcode is often used to change some internals. E.g. the command \makeatletter changes the catcode @. But what is \mathcode and how does it work? catcodes are well explained here: Wiki ...
32
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2answers
825 views

No \makeatletter required?

In typing up some small examples that might create errors in LaTeX (for Documents with typical LaTeX errors), I tried the following: \documentclass{article} \def\my@macro#1{-#1-}% This is magic ...
20
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2answers
671 views

Incompatibility between verbatim and tabu? (Danger of using \scantokens in a package)

With the following MWE \documentclass{article} \usepackage{verbatim} \usepackage{tabu} \makeatletter \renewcommand\verbatim@processline {% \begin{tabu}to\textwidth{|l|X[-1,l]|} ...
14
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2answers
391 views

Macro to take a character as argument, make it active, then \def it.

I have a XeLaTeX document in which I want some unicode symbols to be auto-substituted, like ¼ → 1/4, » → >>, « → <<. But instead of a long list like \catcode`\¼=\active\def¼{1/4} ...
13
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3answers
929 views

How to get the catcode of a token?

For debugging a complicated macro I would like to print out the catcode of a token. Optimally I would like to have a macro \getcatcode such that, for example, \getcatcode{a} would expand to 10. How ...
8
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1answer
312 views

Active characters in linguistics

What are the pros and cons of using active characters instead of macros in text? Would it make sense to implement a “simplified markup” parser in Latex to make code more readable? Rationale ...
7
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3answers
338 views

Trouble defining a macro that typesets underscore characters as _

I want to define a macro that typesets its argument in typewriter font and allows for underscore characters in its argument. Within a group, I make _ active, I define \_ to be typeset as an ...
7
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2answers
522 views

Active characters after \begin{document}

I'm using XeLaTeX and I want to do automatic repeating of plus sign after breakline. I've found the unoffical package for this but it seems to me a bit overkill (although didn't try it). I tried to ...
21
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2answers
874 views

How bad is slack \makeatother discipline really?

Following Will Robertson's admission that Fwiw, i'm not aware of any troubles with a missing \makeatother, but you're right. It's a bad habit of mine to omit it, and my own progressive slackness about ...
12
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1answer
451 views

Using tikzcd in newcommand (for inline arrows)

I’m using tikz-cd for diagrams, and have a medium-sized diagram that I want to re-use several times. However, when I try using a definition like: \newcommand{\myarrow}{$\begin{tikzcd} A \ar{r} & ...
13
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3answers
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Hooking every line of the source code

I've been considering a more radical solution to the problem k.t.hagen posed a while back. Would it be possible (perhaps by catcode hijacking) to put hooks on individual lines of the source code? ...
13
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1answer
522 views

How to redefine @ and . to obfuscate email addresses?

I am writing a small package containing macros I intend to use regularly. Among those macros, I have \mailto with the following definition: \@ifpackageloaded{hyperref}{% \def\mailto#1{% ...
3
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2answers
134 views

How to Disable Function of Underscores?

Code \documentclass{article} \begin{document} http://apps.who.int/iris/bitstream/10665/75146/1/9789241548441_eng.pdf#page=35 \end{document} Output Wanted output: no special effect of ...
13
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1answer
190 views

Is it reasonable to expect an expl3-compatible release of TikZ/PGF in the future? / Workarounds for using TikZ under expl3 syntax

Keeping in mind: TikZ uses space tokens significantly, and expl3 syntax completely disregards whitespace and will only become more prevalent, is it reasonable to expect a future version of TikZ ...
12
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1answer
262 views

Can the makeatletter/makeatother mechanics lead to parsing problems?

The reason for using \makeatletter/\makeatother has been discussed in many places, for instance in this question. However I think that this trick of playing around with the "@" character is itself ...
9
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1answer
140 views

SplitArgument on colon doesn't work under expl3 syntax

\documentclass{article} \usepackage{xparse} \DeclareDocumentCommand\TestA{>{\SplitArgument{1}{:}}m}{% \Example #1 } \ExplSyntaxOn \DeclareDocumentCommand\TestB{>{\SplitArgument{1}{:}}m}{ ...
9
votes
2answers
439 views

Adding newlines while writing text to a file

Within a custom command, I'm doing the following to write to a file: \newcommand\mycommand[1]{ \newwrite\file \immediate\openout\file=foobar.tex \immediate\write\file{ foo bar #1 ...
9
votes
4answers
750 views

How do I get the category code of a character that is the value of a control sequence?

How can I get the category code of a character that is the value of a control sequence? If I do this The catcode for A is \the\catcode`A. I get The catcode for A is 11. If I do this \let\abc=A ...
8
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1answer
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\input only part of a file using catchfilebetweentags package

I would like to include only a part of a .tex file into a different .tex file. The part I want to include is delimited by some comment tags, as it is used by catchfilebetweentags package. I tried the ...
6
votes
1answer
192 views

\scantokens in LuaTeX

The eTeX \scantokens command appears to work differently in LuaTeX than it does in eTeX, pdfTeX and XeTeX. Compiling the following test file with any engine other than LuaTeX performs \show+, which ...
5
votes
1answer
39 views

Repeated “Label(s) may have changed” when using \catcode`_=12 underscore hack with hyperref

This MWE produces repeated Label(s) may have changed warnings despite the output files not changing. The same problem has been discussed in How to diagnose a permanent "Label(s) may have ...
4
votes
1answer
506 views

Generating a catcode table in Latex (with \typeout to terminal)?

I often need to look up a catcode table, and quick searches on the web are rarely satisfying. So I thought, it must be (in the long term) easier to use a Latex function of sorts, to loop through all ...
45
votes
1answer
4k views

Is it \catcode or \catcode`?

I've noticed that \catcode is poorly documented in the TeXbook. The primitive is defined as \catcode but every time it is used, it is used as \catcode` ... the backquote is never discussed. ` itself ...
25
votes
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1k views

Typesetting hashtags with natural syntax

I'm using an online conversation in my document and I've made an environment to use for it. The thing is, there are many #hashtags in each post (that I'd like to color appropriately). To make it ...
15
votes
1answer
240 views

Behavior of \\ in Plain TeX

According to \show, the pre-defined control sequence \\ is supposed expand to its argument without the suffix "pt": This is TeX, Version 3.1415926 (TeX Live 2012/Debian) **\show\\ > \\=macro: ...
12
votes
3answers
552 views

Read strings from file that contains the special character #

I need to read some values from data files as given in the sample code. The problem arises when the files contain # character. Then I get " ! Illegal parameter number in definition of \@xs@call " ...
6
votes
3answers
161 views

Make Characters Active via Macro in Math Mode

I am trying to make characters active in math mode, but can't seem to get past the most basic of examples. I would like to define a macro which is passed: the character to make active and the ...
3
votes
1answer
273 views

Use catcode for alternative way of writing fractions

Writing fractions using different syntax would sometimes be useful, instead of using \frac{ab}{cd}, I would prefer to write something like \frac{ab⌂cd} where the Unicode ⌂ is the }{. n.b., I don't ...
10
votes
1answer
117 views

Is there some reason I can't change catcodes inside a command?

I have a very simple question. When I do this: \catcode`\@=0 \catcode`\\=11 @mycommand{a} @catcode`@\=0 \catcode`\@=11 It works perfectly and calls \mycommand correctly. However, when I try to ...
8
votes
1answer
89 views

real colons in a expl3 context

I'm fighting to find a good way to use colons in an expl3 context. The example uses tcolorbox for a demonstration but I ran into the problem also in other places where a colon was used to delimit an ...
6
votes
1answer
751 views

catcode as used in defining Hypergeometric Function

This is perhaps not a very intelligent question, as I am not (of great intelligence nor) well versed in raw tex, even more so \catcode but in the code given in a previous answer there is a use of ...
5
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1answer
383 views

Active characters inside commands

I'm trying to ease my typesetting of phonetics with tipa by creating a custom command myipa which is supposed to substitute some common characters for the corresponding tipacodes. A much simplified ...
5
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348 views

Setting catcodes in a group

Can someone explain to my why \foo and \bar are not the same (in the \ifx sense) in this example: \documentclass{article} \begingroup \catcode`|=3\relax \gdef\abc{|} \endgroup \makeatletter ...
3
votes
1answer
289 views

Expanding subscript and subscript capabilities

Well, I liked the idea expressed in the question alternative syntax of subscripts using tex. But I want it to work in a sightly different way. I just want to expand the usual _ and ^. How? So that ...
2
votes
2answers
100 views

Keeping underscores in parameters even inside NewEnviron environments

I followed this answer to define a command such that underscores in its parameter can be kept. However, this does not work if the command is called inside an environment that has been defined with ...
13
votes
3answers
633 views

How do I test for a character, irrespective of catcode?

This came up from Labels in TikZ are incorrectly interpreted, but it's also something I've run into with the braids package, and a couple of other things I've done. Also, from looking at the TikZ ...
11
votes
1answer
96 views

Active ! Character Hangs within TikZ

The MWE below makes the ! active in math mode using the solution from Make Characters Active via Macro in Math Mode and uses the tikz \hcancel via Diagonal strikeout starting too low and ending too ...