how to get the right format of a subfigure if i use a custom figure number

I'm a heavy LaTeX user, but have very lite idea how the Tex programming is done. I'm writing a longer document and wanted to have figure numbers like that: chaper.section.figure_number e.g. Figure 4.3.10. After some goggeling i found this solution which works just fine:

\makeatletter
\def\thefigure{\thesection.\@arabic\c@figure}
\def\thetable{\thesection.\@arabic\c@table}
\def\theequation{\thesection.\@arabic\c@equation}
\makeatother


,although I have no Idea why. When I'm using a subfigure with a label unfortunately I get references like that: chaper.figure_nuber e.g. 4.30(a). But what i want is: chapter.section.figure_number.(a,,b,c..) e.g. 4.2.10(a). I guess I have to define an additional command like above, but from the subfig documentation I can't say which and how...

I would appreciate any help

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The following setup should to the job you're after. Note that I use the newer subcaption package instead of the older subfig package and that I make use of the \numberwithin command provided by the amsmath package.

\documentclass{book}
\usepackage{amsmath,    % for \numberwithin and \eqref commands
subcaption} % for subfigure environment
\usepackage[demo]{graphicx} % remove 'demo' option for real document
\numberwithin{equation}{section}
\numberwithin{figure}{section}
\numberwithin{table}{section}

\begin{document}
\chapter{First Chapter}
\section{New ideas}

\begin{figure}[h]
\begin{subfigure}{0.45\textwidth}
\includegraphics[width=\columnwidth]{somegraph.pdf}
\caption{First subfig} \label{fig:1a}
\end{subfigure}
\hspace{\fill} % maximize horizontal separation of subfigs
\begin{subfigure}{0.45\textwidth}
\includegraphics[width=\columnwidth]{anothergraph.pdf}
\caption{First subfig} \label{fig:1b}
\end{subfigure}
\caption{The first figure}
\end{figure}

A display-style equation:
$$\label{eq:1} a^2+b^2=c^2$$

And here are cross-references to subfigures \ref{fig:1a} and \ref{fig:1b}
as well as to equation~\eqref{eq:1}.
\end{document}


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Thank's for your answer. I would rather continue to use the subfigure package since I already have a lot of them in my document... But if there is no other way i will switch to your solution... –  Andre Aug 21 '12 at 6:46