# Referencing to subfigures in main caption

I'm trying to reference to subfigures in the main caption of my figure. Unfortunately I'm only getting blanks, not even undefined referencing ??. What's going on?

\documentclass{report}

\usepackage[superscript]{cite}
\usepackage{mathtools}
\usepackage{graphicx}
\usepackage{caption}
\usepackage{subcaption}

\begin{document}
Some text.

\begin{figure}[!h]
\centering
\begin{subfigure}[b]{0.4\textwidth}
\centering
\includegraphics[width=\textwidth]{figure1}
\label{fig:fig1}
\end{subfigure}
\begin{subfigure}[b]{0.4\textwidth}
\centering
\includegraphics[width=\textwidth]{figure2}
\label{fig:fig2}
\end{subfigure}
\caption{\protect\subref{fig:fig1} shows figure 1 and \protect\subref{fig:fig2} shows figure 2.}
\end{figure}
\end{document}

• Neither of your subfigures actually have a caption. Use \caption{\label{fig:fig1}} and \caption{\label{fig:fig2}} in both subfigures. – Werner Aug 28 '13 at 14:08
• Yes, I left the captions of the subfigures away on purpose. I thought that captions weren't necessary to label subfigures? – Robert Aug 28 '13 at 14:18
• See p 5 of the subcaption documentation for an example very similar to yours. – Werner Aug 28 '13 at 14:21
• If there is no (a), it is not nice to link to a. The lector wouln't know, what you mean. In this case you should write: The above shows figure 1 (left) and figure 2 (right) – LaRiFaRi Aug 28 '13 at 14:25
• @Robert: If the sub-caption labels are "hard-coded" in the figures, then you might just as well "hard-code" the actual reference to them: \caption{(a)~shows Figure~1 and~(b) shows Figure~2}. Because if you wish to switch the subfigures, you'd have to change the "hard-coded" image captions as well. As you now know, LaTeX can handle this without the "hard-coding". – Werner Aug 28 '13 at 14:50

## 2 Answers

You need to add a separate \caption for each subfigure in order to display the label (which can then be referenced):

\documentclass{article}
\usepackage{graphicx}% http://ctan.org/pkg/graphicx
\usepackage{caption,subcaption}% http://ctan.org/pkg/{caption,subcaption}

\begin{document}
Some text.

\begin{figure}[ht]
\centering
\begin{subfigure}[b]{0.5\linewidth}
\centering\includegraphics[width=100pt]{example-image-a}
\caption{\label{fig:fig1}}
\end{subfigure}%
\begin{subfigure}[b]{0.5\linewidth}
\centering\includegraphics[width=100pt]{example-image-b}
\caption{\label{fig:fig2}}
\end{subfigure}
\caption{\subref{fig:fig1} shows Figure~1 and~\subref{fig:fig2} shows Figure~2.}
\end{figure}
\end{document}


Taken from the subcaption documentation, section "Referencing sub-figures without sub-captions":

If you don’t want to give a sub-figure a caption, because the picture itself already contains the caption, or for some other reason, you can use the command \phantomsubcaption instead of \subcaption, or – when inside a subfigure or subtable environ- ment – \phantomcaption instead of \caption. \phantomsubcaption and \phantomcaption do not have any arguments, and they do not generate any output, but give you an anchor for a \label command which can be placed afterwards. Fur- thermore it increases the sub-figure resp. sub-table counter. Please note that – just like \subcaption – the \phantomsubcaption command must be applied inside its own group, box, or environment.

\documentclass{report}

\usepackage[superscript]{cite}
\usepackage{mathtools}
\usepackage[demo]{graphicx}
\usepackage{caption}
\usepackage{subcaption}

\begin{document}
Some text.

\begin{figure}[!h]
\centering
\begin{subfigure}[b]{0.4\textwidth}
\centering
\includegraphics[width=\textwidth]{figure1}
\phantomcaption
\label{fig:fig1}
\end{subfigure}
\begin{subfigure}[b]{0.4\textwidth}
\centering
\includegraphics[width=\textwidth]{figure2}
\phantomcaption
\label{fig:fig2}
\end{subfigure}
\caption{\subref{fig:fig1} shows figure 1 and \subref{fig:fig2} shows figure 2.}
\end{figure}
\end{document}


Note: \phantomsubcaption needs subcaption version 1.1 (2011/08/17) or newer.