"Missing number, treated as zero" error adding subfigures

Question

I was ok doing my college work, then I needed to put figures on it. I looked at the Wikipedia's example where it used subfigures, so I tried to use in my work.

The following block (copy-and-paste with changed figure paths):

\begin{figure}
    \centering
    \begin{subfigure}[b]{0.3\textwidth}
        \includegraphics[width=\textwidth]{multiple/Torrentcomp_small-0.png}
        \caption{A gull}
        \label{fig:gull}
    \end{subfigure}%
    ~ %add desired spacing between images, e. g. ~, \quad, \qquad etc.
      %(or a blank line to force the subfigure onto a new line)
    \begin{subfigure}[b]{0.3\textwidth}
        \includegraphics[width=\textwidth]{multiple/Torrentcomp_small-0.png}
        \caption{A tiger}
        \label{fig:tiger}
    \end{subfigure}
    ~ %add desired spacing between images, e. g. ~, \quad, \qquad etc.
      %(or a blank line to force the subfigure onto a new line)
    \begin{subfigure}[b]{0.3\textwidth}
        \includegraphics[width=\textwidth]{multiple/Torrentcomp_small-0.png}
        \caption{A mouse}
        \label{fig:mouse}
    \end{subfigure}
    \caption{Pictures of animals}\label{fig:animals}
\end{figure}

I compiled and then got the following log before some preexistent warnings

./Chapters/Chapter3.tex:26: Missing number, treated as zero. [        \begin{subfigure}[b]{0.3\textwidth}]
./Chapters/Chapter3.tex:26: Illegal unit of measure (pt inserted). [        \begin{subfigure}[b]{0.3\textwidth}]
./Chapters/Chapter3.tex:33: Missing number, treated as zero. [        \begin{subfigure}[b]{0.3\textwidth}]
./Chapters/Chapter3.tex:33: Illegal unit of measure (pt inserted). [        \begin{subfigure}[b]{0.3\textwidth}]
./Chapters/Chapter3.tex:40: Missing number, treated as zero. [        \begin{subfigure}[b]{0.3\textwidth}]
./Chapters/Chapter3.tex:40: Illegal unit of measure (pt inserted). [        \begin{subfigure}[b]{0.3\textwidth}]

(...)

./Chapters/Chapter3.tex:46: LaTeX Warning: Float too large for page by 833.1359pt on input line 46.

I thought that it was that \textwidth fault, but then \the\textwidth printed some value. So, I'm stuck in this. =/

Answer 1

You are probably using an obsolete package, subfigure. Use subcaption instead.

Taking the subcaption example from wikibooks (name of *.png changed):

\documentclass{article}

\usepackage{graphicx}
%\usepackage{subfigure}
\usepackage{caption}
\usepackage{subcaption}

\begin{document}

\begin{figure}
    \centering
    \begin{subfigure}[b]{0.3\textwidth}
        \includegraphics[width=\textwidth]{it}
        \caption{A gull}
        \label{fig:gull}
    \end{subfigure}%
    ~ %add desired spacing between images, e. g. ~, \quad, \qquad etc.
      %(or a blank line to force the subfigure onto a new line)
    \begin{subfigure}[b]{0.3\textwidth}
        \includegraphics[width=\textwidth]{it}
        \caption{A tiger}
        \label{fig:tiger}
    \end{subfigure}
    ~ %add desired spacing between images, e. g. ~, \quad, \qquad etc.
      %(or a blank line to force the subfigure onto a new line)
    \begin{subfigure}[b]{0.3\textwidth}
        \includegraphics[width=\textwidth]{it}
        \caption{A mouse}
        \label{fig:mouse}
    \end{subfigure}
    \caption{Pictures of animals}\label{fig:animals}
\end{figure}

\end{document}

Answer 2

Maybe the problem is that the name of your file contains an underscore ("_"). We had the same problem and it was fixed changing the name of the file.