Is there a way to prevent caption package from changing counters beforehand

Question

Example:

\documentclass{article}

\usepackage{graphicx}

\begin{document}
\newcounter{counter}
\setcounter{counter}{1}

\begin{figure}
    \includegraphics{example-image}
    \caption
    {
        \thecounter
        \protect\stepcounter{counter}
        \thecounter
        \protect\stepcounter{counter}
        \thecounter
        \protect\stepcounter{counter}
    }
\end{figure}    
\end{document}

When I run it without caption package, I will get 1 2 3 in caption. But when I add usepackage{caption} it will output 4 5 6. Is there a way to prevent this?

Answer 1

The problem is, that caption need to internally typeset the caption more than once, to do the single line check and either print the single or the multi line caption. So with option singlelinecheck=false, the problem already does not occur but results in a different alignment of single line captions:

\documentclass{article}

\usepackage{graphicx}
\usepackage[singlelinecheck=false]{caption}

\newcounter{counter}
\setcounter{counter}{1}

\begin{document}% Moved to do all declarations in the preamble!
\begin{figure}
    \includegraphics{example-image}
    \caption
    {
        \thecounter
        \protect\stepcounter{counter}
        \thecounter
        \protect\stepcounter{counter}
        \thecounter
        \protect\stepcounter{counter}
    }
\end{figure}    
\end{document}

Package caption also provides a hook to execute some code before doing the single line check. So you could deactivate \stepcounter inside the single line check:

\documentclass{article}

\usepackage{graphicx}
\usepackage{caption}

\newcounter{counter}
\setcounter{counter}{1}
\makeatletter
\AtCaptionSingleLineCheck{\let\stepcounter\@gobble}
\makeatother

\begin{document}% Moved to do all declarations in the preamble!

\begin{figure}
    \includegraphics{example-image}
    \caption
    {
        \thecounter
        \protect\stepcounter{counter}
        \thecounter
        \protect\stepcounter{counter}
        \thecounter
        \protect\stepcounter{counter}
    }
\end{figure}    
\end{document}

But note, that with this very simple deactivation of \stepcounter the decision to use a single line caption instead of a multi line caption can be wrong, i.e., if one of the \stepcounter would change the number of digits of the counter (or generally the output width). So maybe using

\documentclass{article}

\usepackage{graphicx}
\usepackage{caption}

\newcounter{counter}
\setcounter{counter}{1}
\makeatletter
\AtCaptionSingleLineCheck{%
  \renewcommand*{\stepcounter}[1]{\expandafter\advance\@nameuse{c@#1}\@ne\relax}%
}
\makeatother
\begin{document}% Moved to do all declarations in the preamble!

\begin{figure}
    \includegraphics{example-image}
    \caption
    {
        \thecounter
        \protect\stepcounter{counter}
        \thecounter
        \protect\stepcounter{counter}
        \thecounter
        \protect\stepcounter{counter}
    }
\end{figure}    
\end{document}

would be better.

Note: Both solutions do only work as long as the single line check is done inside a group (as it is currently and IMHO will be in future, too).

Caveat: You are also writing \setcounter{counter} to the lof-file. So adding \listoffigures will also change your result, because the counter will also be increased while printing the List of Figures. So the LoF will not show the same numbers as the caption itself. However, this wasn't the question. So if you need an answer how to change this, please ask another question.

Answer 2

I guess you want subcaption and its subcaptiongroup, \phantomcaption and subref features.

\documentclass{article}

\usepackage{graphicx}
\usepackage{subcaption}

\begin{document}

\begin{figure}
\centering
\renewcommand{\thesubfigure}{\arabic{subfigure}}

\begin{subcaptiongroup}
\includegraphics[width=4cm]{example-image}

\phantomcaption\label{first}

\phantomcaption\label{second}

\phantomcaption\label{third}
\end{subcaptiongroup}
\caption{\subref{first} \subref{second} \subref{third}}
\end{figure}    

\end{document}

The blank lines are meant not to create spurious spaces.