Xrhrft

After I had a macro that worked, I tried to improve it by making some parameters optional.
Unfortunately the macro no longer works. Instead I'm getting errors I do not understand, for example:

LaTeX Warning: Label `####5' multiply defined.

LaTeX Warning: Label `####5' multiply defined.

! LaTeX Error: fLab undefined.

! Illegal parameter number in definition of fLab.

! Illegal parameter number in definition of reserved@a.

! LaTeX Error: fCap undefined.

...and so on.
The last code I tried looked like this:

%% Graphics figure with caption and label

% [1:placement,] 2:relative width, 3:file name[, 4:caption[, 5:label]]

newcommand{figCapLab}[5][htbp]{%

ifthenelse{equal{#5}{}}%

{renewcommand{fLab}{}}%

{renewcommand{fLab}{label{##5}}}%

ifthenelse{equal{#4}{}}%

{renewcommand{fCap}{fLab}}%

{renewcommand{fCap}{caption{fLab{small{}##4}}}}%

begin{figure}[#1]%

centering%

begin{minipage}[t]{#2textwidth}%

includegraphics[width=textwidth]{#3}% is width of surrounding minipage

fCap%

end{minipage}%

end{figure}

}

%% Graphics figure with caption

% [1:placement,] 2:relative width, 3:file name, 4:caption

newcommand{figCap}[4]{%

ifthenelse{equal{#1}{}}%

{figCapLab{#2}{#3}{#4}{}}%

{figCapLab[#1]{#2}{#3}{#4}{}}%

}

%% Graphics figure with label

% [1:placement,] 2:relative width, 3:file name, 4:label

newcommand{figLab}[4]{%

ifthenelse{equal{#1}{}}%

{figCapLab{#2}{#3}{}{#4}}%

{figCapLab[#1]{#2}{#3}{}{#4}}%

}

Who can explain what went wrong?

People who like complete examples should add this prolog:

documentclass[a4paper,twoside]{report}

usepackage{german}

usepackage[latin1]{inputenc}

usepackage{a4}

usepackage{amsmath}

usepackage{url}

usepackage{graphicx}

usepackage{ifthen}

...and this epilog:

begin{document}

See ref{foo}.

figCapLab{0.9}{whatever.pdf}{Caption}{foo}

end{document}

documentclass{article}

usepackage{graphicx}

newcommandaddtofigtoks[1]{expandafterfigtoksexpandafter

  {thefigtoks#1}}

newtoksfigtoks

newcommandfigCapLab[3][htbp]{%

  figtoks{begin{figure}[#1]}

  addtofigtoks{centering}

  addtofigtoks{includegraphics[width=#2textwidth]{#3}}

  optcap

}

newcommandoptcap[1][relax]{%

  ifxrelax#1relax

    addtofigtoks{end{figure}}

    thefigtoks

  else

    addtofigtoks{caption{#1}}%

    expandafterlabelopt

  fi

}

newcommandlabelopt[1][relax]{%

  ifxrelax#1relaxelseaddtofigtoks{label{#1}}fi

  addtofigtoks{end{figure}}

  thefigtoks

}

begin{document}

figCapLab{.2}{example-image-a}

figCapLab{.2}{example-image-b}[My caption]

figCapLab{.2}{example-image-c}[My caption][fg:label1]

figCapLab[p]{.2}{example-image}[Other caption][fg:label2]



In figures ref{fg:label1} and ref{fg:label2}...

end{document}

Ack-shu-ally, the more I think of it, tokens are not even needed:

documentclass{article}

usepackage{graphicx}

newcommandfigCapLab[3][htbp]{%

  begin{figure}[#1]

  centering

  includegraphics[width=#2textwidth]{#3}

  optcap

}

newcommandoptcap[1][relax]{%

  ifxrelax#1relax

    end{figure}

  else

    caption{#1}%

    expandafterlabelopt

  fi

}

newcommandlabelopt[1][relax]{%

  ifxrelax#1relaxelselabel{#1}fi

  end{figure}

}

begin{document}

figCapLab{.2}{example-image-a}

figCapLab{.2}{example-image-b}[My caption]

figCapLab{.2}{example-image-c}[My caption][fg:label1]

figCapLab[p]{.2}{example-image}[Other caption][fg:label2]



In figures ref{fg:label1} and ref{fg:label2}...

end{document}

Here is how you can achieve your goal using xparse:

documentclass{article}



usepackage{graphicx,xparse}



% figCapLab

%   [<float spec>]   #1

%   {<width factor>} #2

%   {<image>}        #3

%   [<caption>]      #4

%   [<label>]        #5

NewDocumentCommand{figCapLab}{ O{htbp} m m o o }{%

  begin{figure}[#1]

    centering

    includegraphics[width=#2linewidth]{#3}% Set image at width

    IfValueT{#4}

      {caption{#4}IfValueT{#5}{label{#5}}}% Set possible caption and label

  end{figure}

}



begin{document}



figCapLab{.2}{example-image-a}

figCapLab{.2}{example-image-b}[My caption]

figCapLab{.2}{example-image-c}[My caption][fg:label1]

figCapLab[p]{.2}{example-image}[Other caption][fg:label2]



In figures ref{fg:label1} and ref{fg:label2}ldots



end{document}

Optional arguments with a default is specified using O{<default>} while optional arguments without a default uses o. Conditioning on whether or not a value is supplied is done using IfValueTF{<parameter>}{<true>}{<false>}. There are also singular conditionals IfValueT and IfValueF, the former of which was used above.

The above code assumes that an empty caption (blank fourth argument) would not need a label (fifth) argument. If that's needed, move the IfValueT{#5}{label{#5}} out of the <true> branch inside IfValueT{#4}:

NewDocumentCommand{figCapLab}{ O{htbp} m m o o }{%

  begin{figure}[#1]

    centering

    includegraphics[width=#2textwidth]{#3}% Set image at width

    IfValueT{#4}{caption{#4}}% Possible caption

    IfValueT{#5}{label{#5}}% Possible label

  end{figure}

}