Defining custom labels

Question

Is it possible to define a directive which creates a custom label which I can later reference on multiple locations with \ref{...}?

For example:

...
\createlabel{l-foo}{22}
...
% later in document:
In line \ref{l-foo} foo-bar. Furthermore, line \ref{l-foo}...
...

Should get translated into:

In line 22 foo-bar. Furthermore, line 22...

Alternatively, is there a way to define a set of predefined values somewhere in the beginning of the document (it doesn't have to be the label mechanism) so that I can later use them in the text.

Answer 1

Do you really need to use \ref? You could just say \newcommand{\foobar}{22}, so that when you type \foobar you get 22. Of course this crude approach does not work if any references occur before the label is defined. To do it with \ref, try this.

\documentclass{minimal}
\makeatletter
\newcommand{\customlabel}[2]{%
\protected@write \@auxout {}{\string \newlabel {#1}{{#2}{}}}}
\makeatother
\begin{document}
Here is some text. \customlabel{foobar}{22}
Here is some more text \ref{foobar}.
\end{document} 

Answer 2

I found a solution for the custom label what works with hyperref, been looking everywhere and I keep ending back to this page. (By google searching)

Solution by Ian (does not work with hyperref)

\makeatletter
\newcommand{\customlabel}[2]{%
\protected@write \@auxout {}{\string \newlabel {#1}{{#2}{}}}}
\makeatother

The reason it does not work with hyperref, is that the package change the \newlabel command so it has 6 parameters.

Modified version of Ian's answer, that works with hyperref package.

\makeatletter
\newcommand{\customlabel}[2]{%
   \protected@write \@auxout {}{\string \newlabel {#1}{{#2}{\thepage}{#2}{#1}{}} }%
   \hypertarget{#1}{#2}
}
\makeatother

However doing this means that the modified version requires hyperref package.

\hypertarget is added to make the links work when using \ref.

Answer 3

\documentclass{article}

\usepackage{lineno}

\begin{document}

\linenumbers

\modulolinenumbers[255] % To switch off the showing of the numbers on margins

Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Ut purus
elit, vestibulum ut, placerat ac, adipiscing vitae, felis. Curabitur
dictum gravida mauris. \linelabel{line:Nam}Nam arcu libero,
nonummy eget, consectetuer id, vulputate a, magna. Donec vehicula
augue eu neque. Pellentesque habitant morbi tristique senectus et
netus et malesuada fames ac turpis egestas. Mauris ut leo. Cras
viverra metus rhoncus sem. Nulla et lectus vestibulum urna fringilla
ultrices.  Phasellus eu tellus sit amet tortor gravida placerat.
Integer sapien est, iaculis in, pretium quis, viverra ac, nunc.
Praesent eget sem vel leo ultrices bibendum.  Aenean faucibus.  Morbi
dolor nulla, malesuada eu, pulvinar at, mollis ac, nulla.  Curabitur
auctor semper nulla. Donec varius orci eget risus. Duis nibh mi,
congue eu, accumsan eleifend, sagittis quis, diam. Duis eget orci sit
amet orci dignissim rutrum

The sentence ``Nam arcu libero'' starts at line~\ref{line:Nam}

\end{document}

Answer 4

I guess the shortest solution is to use \def:

\documentclass[a4paper,oneside,11pt]{report}

\def \lfoo {22 }

\begin{document}
    In line \lfoo foo-bar. Furthermore, line \lfoo...
\end{document}

Answer 5

what about this:

\makeatletter
\newcommand{\mylabel}[2]{%
 \@bsphack\begingroup
 \def\@currentlabel{#2}%
 \label{#1}%
 \endgroup\@esphack
}
\makeatother

another example - define custom labels for a new environment:

\makeatletter%
\newenvironment{myenvironment}{%
 \addtocounter{mycounter}{1}%
 \def\@currentlabel{{\thesection.\themycounter}}%  custom labelling for this environment
 %%... etc.,  other environment definitions here
}{%
%...
}
\makeatother

Answer 6

I am not sure I understand. I think this answer the question (no use of aux file)

Edit: as mentioned below by egreg this work only if \refis called after \createlabel

\documentclass{article}
\makeatletter
\newcommand{\createlabel}[2]{%
\@bsphack
\expandafter\edef\csname #1\endcsname{#2}\@esphack}
\makeatother
\newcommand{\Ref}[1]{\csname #1\endcsname}
\begin{document}
test
\createlabel{l-foo}{22} and leater \Ref{l-foo}
\end{document}

Answer 7

Hyperref-proof solution (1. works with hyperref, 2. also adds hyperlinks to the \xlabel):

You can use \nameref which is part of hyperref :

\documentclass{article}

\usepackage{hyperref}
\newcommand{\xref}{\nameref}
\makeatletter
\newcommand\xlabel[2][]{\phantomsection\def\@currentlabelname{#1}\label{#2}}
\makeatother

\begin{document}

We call $t$ {\em positive}\xlabel[positive]{pos} if $t>0$. Now ...

\bigskip

Assume that $s$ is \xref{pos}. Then ...

Recall the definition of \hyperref[pos]{positivity}

\end{document}

Now \xref{pos} prints "positive" with a hyperlink to the definition (xlabel). (The \hyperref above prints the customized text "positivity" instead of "positive". To produce hyperlinks without )

To avoid repetition, you can just write \emxlabel{positive}{pos} above once you define:

\newcommand{\emxlabel}[2]{{\em #1}\xlabel[#1]{#2}}

Similarly, you can use the following for itemized lists:

\newcommand{\itempxlabel}[1]{\item[\bf (#1)]\xlabel[(#1)]{#1}} 

To make the [first argument] equal to the {second} if not given, use this code (or see here):

\usepackage{xifthen}
\makeatletter
\newcommand{\xlabel}[2][]{\phantomsection\def\@currentlabelname{\ifthenelse{\equal{#1}{}}{#2}{#1}}\label{#2}} 
\makeatother

More sophisticated systems are possible with packages like glossaries or acronym. The above solution is essentially due to Ulrike Fischer.

Benefits:

1. You can change the appearance of the \xref{pos} later on just by changing the first argument of \xlabel. (Also the other solutions have this benefit except that some of them stop working if you \usepackage{hyperref}.)
2. \xref{pos} also produces a hyperlink. By clicking it you get to the definition (\xlabel). TexShop also shows a hover (mouseover) text (the definition). I don't know how to get the hovertext to TeXStudio.

Add the following lines to your .cwl file (and restart TeXstudio) to allow for auto-completion of \xref label (and to include \xlabel labels etc. into that list):

\xref{label}#r
\xlabel{label}#l
\itempxlabel{label}#l
\emxlabel{label}#l

If you use the {xifthen} formulation of \xlabel, then its .cwl line shoud read

\xlabel[nonlabel]{label}#l 

Answer 8

If you use the cleveref package, you can also use the \crefname command and then use an optional argument in the \label command.

The following example is borrowed from Mico from here:

\documentclass{article}
\usepackage[colorlinks=true]{hyperref}
\usepackage[nameinlink]{cleveref}    
% provide singular and plural names of the categories "car" and "truck"
\crefname{truck}{truck}{trucks}
\crefname{car}{car}{cars}

\begin{document}
\section{Section One}\label[car]{sec:1}
\section{Section Two}\label[truck]{sec:2}
\section{Section Three}
Cross-references to \cref{sec:1,sec:2}.
\end{document}