Longtable Caption Spacing

Question

I am writing a thesis, using a customized document class that I haven't created, but seems to function similarly to article. I have been using longtable for my tables, but am struggling to make the captions single spaced without affecting the spacing of the table contents. I am using the longtable and setspacing packages, and have used \renewcommand{\arraystretch}{0.7} to make the text within the table 0.7 spaced.

I would now like to make the captions single spaced, but am not sure how to separate the command for the caption and for the table contents.

longtable caption formatting had a similar question and \AtBeginEnvironment{longtable}{\linespread{1}\selectfont} was recommended, however that changes the spacing for the whole table, not just the caption. I have tried \captionsetup[longtable]{\linespread{1}\selectfont} however this seems to crash LaTeX.

I feel as though this should be quite simple, and that something along the lines of \AtBeginEnvironment{longtable}{\singlespacing} should be all it takes, though that produces errors (I assume because I already have the \arraystretch command in there). If someone can point me in the right direction it would be greatly appreciated!

Answer 1

LT captions are set by

\def\LT@makecaption#1#2#3{%
  \LT@mcol\LT@cols c{\hbox to\z@{\hss\parbox[t]\LTcapwidth{%
    \sbox\@tempboxa{#1{#2: }#3}%
    \ifdim\wd\@tempboxa>\hsize
      #1{#2: }#3%
    \else
      \hbox to\hsize{\hfil\box\@tempboxa\hfil}%
    \fi
    \endgraf\vskip\baselineskip}%
  \hss}}}

so you could use

\makeatletter
\def\LT@makecaption#1#2#3{%
  \LT@mcol\LT@cols c{\hbox to\z@{\hss\parbox[t]\LTcapwidth{%
    \sbox\@tempboxa{#1{#2: }#3}%
    \ifdim\wd\@tempboxa>\hsize
  \singlespacing
      #1{#2: }#3%
    \else
      \hbox to\hsize{\hfil\box\@tempboxa\hfil}%
    \fi
    \endgraf\vskip\baselineskip}%
  \hss}}}
  \makeatother

sorry about the user interface (it's possible that the caption package adds a hook to make this look a bit more natural)