# Why cleveref is not capturing float from pseudo+tcolorbox?

I am switching to pseudo to present my algorithms. Following the documentation, I combined it withtcolorbox to create a floating environment called algorithm.

But when I want to reference it with \cref from cleveref package, the command is not able to capture the floating environment related to it. Therefore I get ?? 1 instead of alg: 1 (or something like that).

Here is a MWE:

\documentclass{article}

\usepackage{tcolorbox} % colored box with a lot of flexibility
\tcbuselibrary{skins,theorems} % extra lib for pseudo

\usepackage{pseudo} % for pseudocode
\newtcbtheorem{algorithm}{Algorithm}{pseudo/booktabs, float}{alg} % create a float env for algorithms

\usepackage{cleveref}

\begin{document}

\begin{algorithm}{Euclid’s algorithm, \pr{Euclid}(a, b)}{euclid}
\textbf{Input:}  Two positive integers, $a$ and $b$.\\
\textbf{Output:} The greatest common divisor of $a$ and $b$.
\begin{pseudo}[label=\small\arabic*, indent-mark]
while $a \neq b$ \ct{If equal, both are gcd} \\+
if $a > b$ \ct{ Reduce max with multiple of min} \\+
$a = a - b$ \ct{ $a$ is largest} \\-
else $b = b - a$ \ct{ $b$ is largest} \\-
return $a$ \ct{ Both are gcd, so return one}
\end{pseudo}
The running time is quadratic in the number of bits in the input.
\end{algorithm}

A sentence with a clever reference \cref{alg:euclid}.

\end{document}


How could I solve this problem ?

Just set the label type for your new tcolorbox with label type=algorithm:

\documentclass{article}

\usepackage{tcolorbox} % colored box with a lot of flexibility
\tcbuselibrary{skins,theorems} % extra lib for pseudo

\usepackage{pseudo} % for pseudocode

\usepackage{cleveref}

\newtcbtheorem{algorithm}{Algorithm}{label type=algorithm,pseudo/booktabs, float}{alg} % create a float env for algorithms

\begin{document}

\begin{algorithm}{Euclid’s algorithm, \pr{Euclid}(a, b)}{euclid}
\textbf{Input:}  Two positive integers, $a$ and $b$.\\
\textbf{Output:} The greatest common divisor of $a$ and $b$.
\begin{pseudo}[label=\small\arabic*, indent-mark]
while $a \neq b$ \ct{If equal, both are gcd} \\+
if $a > b$ \ct{ Reduce max with multiple of min} \\+
$a = a - b$ \ct{ $a$ is largest} \\-
else $b = b - a$ \ct{ $b$ is largest} \\-
return $a$ \ct{ Both are gcd, so return one}
\end{pseudo}
The running time is quadratic in the number of bits in the input.
\end{algorithm}

A sentence with a clever reference \cref{alg:euclid}.

\end{document}


This is slightly better/easier than setting \crefname for the internal tcb counter, as suggested by @egreg, since you don't need to deal with the internal counter name and it already deals with \Crefname too, depending on your caps options.

Alternatively, if you prefer or need to set crefname, you can do so using tcolorbox's corresponding option (this is pretty much the example from pseudo's user manual):

\documentclass{article}

\usepackage{tcolorbox} % colored box with a lot of flexibility
\tcbuselibrary{skins,theorems} % extra lib for pseudo

\usepackage{pseudo} % for pseudocode

\usepackage{cleveref}

\newtcbtheorem[crefname = {algorithm}{algorithms}]{algorithm}{Algorithm}{pseudo/booktabs, float}{alg} % create a float env for algorithms

\begin{document}

\begin{algorithm}{Euclid’s algorithm, \pr{Euclid}(a, b)}{euclid}
\textbf{Input:}  Two positive integers, $a$ and $b$.\\
\textbf{Output:} The greatest common divisor of $a$ and $b$.
\begin{pseudo}[label=\small\arabic*, indent-mark]
while $a \neq b$ \ct{If equal, both are gcd} \\+
if $a > b$ \ct{ Reduce max with multiple of min} \\+
$a = a - b$ \ct{ $a$ is largest} \\-
else $b = b - a$ \ct{ $b$ is largest} \\-
return $a$ \ct{ Both are gcd, so return one}
\end{pseudo}
The running time is quadratic in the number of bits in the input.
\end{algorithm}

A sentence with a clever reference \cref{alg:euclid}.

\end{document}


This is strictly equivalent to @egreg's answer in its effects, except you don't need to know/worry about the internal name of the tcolorbox counter.

You get the warning

LaTeX Warning: cref reference format for label type tcb@cnt@algorithm'
undefined on input line 26.


Define the format.

And, please, don't have spaces after open parentheses (or before closed ones) if you don't want that your readers' eyes bleed.

\documentclass{article}

\usepackage{tcolorbox} % colored box with a lot of flexibility
\tcbuselibrary{skins,theorems} % extra lib for pseudo
\usepackage{pseudo} % for pseudocode
\usepackage{cleveref}

% create a float env for algorithms
\newtcbtheorem{algorithm}{Algorithm}{pseudo/booktabs, float}{alg}

\crefname{tcb@cnt@algorithm}{algorithm}{algorithms}

\begin{document}

\begin{algorithm}{Euclid’s algorithm, \pr{Euclid}(a, b)}{euclid}
\textbf{Input:}  Two positive integers, $a$ and $b$.\\
\textbf{Output:} The greatest common divisor of $a$ and $b$.
\begin{pseudo}[label=\small\arabic*, indent-mark]
while $a \neq b$ \ct{If equal, both are gcd} \\+
if $a > b$ \ct{Reduce max with multiple of min} \\+
$a = a - b$ \ct{$a$ is largest} \\-
else $b = b - a$ \ct{$b$ is largest} \\-
return $a$ \ct{Both are gcd, so return one}
\end{pseudo}
The running time is quadratic in the number of bits in the input.
\end{algorithm}

A sentence with a clever reference to \cref{alg:euclid}.

\end{document}
`

• Indeed, I should have paid more attention to my warnings. In fact, your solution also solved another of my problems :)
– R. N
Apr 22 at 9:23