[Tex/LaTex] String replacement in LaTeX

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I'd like to know how to replace parts of a string in LaTeX. Specifically I'm given a measurement (like 3pt, 10mm, etc) and I'd like to remove the units of that measurement (so 3pt–>3, 10mm–>10, etc). The reason why I'd like a command to do this is in the following piece of code:

\newsavebox{\mybox}
\sbox{\mybox}{Hello World!}
\newlength{\myboxw}
\settowidth{\myboxw}{\usebox{\mybox}}
\begin{picture}(\myboxw,\myboxw)
\end{picture}

Basically I create a savebox called mybox. I insert the words "Hello World" into mybox. I create a new length, called myboxw. I then get the width of mybox, and store this in myboxw. Then I set up a square picture environment whose dimensions correspond to myboxw. The trouble is that myboxw is returning something of the form "132.56pt", while the input to the picture environment has to be dimensionless: \begin{picture}{132.56, 132.56}.

So, I need a command which will strip the units of measurement from a string.

Best Answer

The internal LaTeX macro \strip@pt returns a length in pt without the unit. For example, if you set \myboxw to 10 mm, it will have a length of 28.45274 pt, and this code

\makeatletter
\strip@pt\myboxw
\makeatother

will output just 28.45274. So you could use this or define your own command like:

\makeatletter
\newcommand*{\stripunit}[1]{\strip@pt#1}
\makeatother

\strip@pt uses \the on a dimen register and strips pt, that's why you did not get 10 (mm) but the corresponding value in pt without unit. Such a conversion to pt and stripping pt seems better to me than just doing string replacement getting some value without knowing the unit.

You can see the source code of \strip@pt with comment if you look into source2e.pdf in section 26.1 Macros for the user (part of the section 26. Selecting a new font), you could open it at the command prompt by typing texdoc source2e or get it from CTAN.

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[Tex/LaTex] Using string variable with LaTeX

You can use a standard \renewcommand to modify the text:

enter image description here

\documentclass{article}
\newcommand{\someSpecialText}{A text that can be changed locally\ldots}
\newcommand{\testIt}{The value of \texttt{someSpecialText} is : ``\someSpecialText''.}

\begin{document}

% The default behavior.
\testIt

% Here I would like to change the definition of `\someSpecialText`
% or anywhere else in the document.
{% Start of group
\renewcommand{\someSpecialText}{A text that \textit{was} changed locally\ldots}
\testIt
}% End of group

% The default behavior.
\testIt

\end{document}

In the above example, the \renewcommand was placed inside a group, defined by the braces { and } to localize the redefinition. If this behaviour is not desired, simply remove the braces to make the redefinition global from that point forward.

Of course, one can also write this in a macro form, which could be considered "shorter", with some default value. Here is an example:

enter image description here

\documentclass{article}
\newcommand{\testIt}[1][A text that can be changed locally\ldots]{The value passed to \texttt{testIt} is : ``#1''.}

\begin{document}

% The default behavior.
\testIt

% Here I would like to change the definition of `\someSpecialText`
% or anywhere else in the document.
\testIt[A text that \textit{was} changed locally\ldots]

% The default behavior.
\testIt

\end{document}

\testIt is set up to output something with a default value. However, you can supply an optional argument that modifies the default behaviour.

[Tex/LaTex] from string to command

TeX is a macro replacement language. That means that when we do

\def\foo{bar}

TeX simply stores bar as the replacement text for \foo. Thus when we use \foo, TeX replaces it exactly with bar, and carries on working. The content of a macro is not a string: it's a token list: thus we can do

\def\fooa{\foob}
\def\foob{bar}

and see the same outcome (TeX replaces \fooa with \foob,then \foob with bar). LaTeX's \newcommand is a wrapper around \def, so the principal is identical (although \newcommand will complain if \foo already exists, which \def will not).

The \gdef primitive works in the same way as \def except it applies globally (\def is local, obeying TeX's grouping system). Thus

\newcommand{\AuthorNames}[1]{\gdef\@AuthorNames{#1}}

works by defining \@AuthorNames as a macro to be replaced by whatever is given as the argument to \AuthorNames. As mentioned in the comments, this approach means that the user has a simple interface

\AuthorNames{whatever}

rather than needing to know \gdef and why it should be used here.

TeX also has another form of token storage: the token register or 'toks'. There are reasons for picking a toks over a macro for storage in some cases. However, most of the time you can happily use a macro: they are in many ways more convenient.

Best Answer

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[Tex/LaTex] Using string variable with LaTeX

[Tex/LaTex] from string to command

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