Problem with lengths

Question

I'm trying to insert some space between the label and the form control in hyperref forms. The following example works:

\documentclass{scrartcl}

\usepackage{calc}
\usepackage{hyperref}

\newcommand\insertlabel[1]{%
    % \newlength\twidth
    % \setlength\twidth{10em-\widthof{#1}}}
    #1:\hspace{4em}
}

\begin{document}
    \begin{Form}
        \TextField{\raisebox{.9ex}{\insertlabel{Name}}}
    \end{Form}
\end{document

But the following doesn't work:

\documentclass{scrartcl}

\usepackage{calc}
\usepackage{hyperref}


\newcommand\insertlabel[1]{%
    \newlength\twidth
    \setlength\twidth{10em}
    #1:\hspace{\twidth-\widthof{#1}}
}

\begin{document}
    \setlength\parindent{0pt}
    \begin{Form}
        \TextField{\raisebox{.9ex}{\insertlabel{Name}}} \\
    \end{Form}    
\end{document}

Can somebody please tell me what the problem is?

Answer 1

Just remove the newlength from the newcommand and place it over it.

\documentclass{scrartcl}

\usepackage{calc}
\usepackage{hyperref}
\newlength{\twidth}
\newcommand\insertlabel[1]{%
    \setlength\twidth{10em-\widthof{#1}}
    #1:\hspace{\twidth}
}

\begin{document}
\setlength\parindent{0pt}
    \begin{Form}
        \TextField{\raisebox{.9ex}{\insertlabel{Name}}} 
    \end{Form}
\end{document}

\newlength command has to be given in preamble... and your command call it from inside the document.

Also, hspace needs a lenght as an argument and not calculations of a length. Calculated before used here.

Finally I removed the \\ that creates unnecessary underfull hbox