Is there really something wrong with using the caption package for \ContinuedFloat?

Question

In my question How to create an unnumbered algorithm with a caption?, a nice solution was suggested using \ContinuedFloat, from the caption package. However, when I use it, I get:

Package caption Warning: Unsupported document class (or package) detected,
(caption)                usage of the caption package is not recommended.
See the caption package documentation for explanation.

The package documentation says:

Please note: Many document classes already have built-in options and commands for customizing captions. If these possibilities are sufficient for you, there is usually no need for you to use the caption package at all. And if you are just interested in using the command \captionof, loading of the very small 'capt-of' package is usually sufficient.

but that's not what I'm after. I'm using a document class I've created as a (thin) wrapper based on report; I don't provide any built-ins I can use instead of \ContinuedFloat, and neither does report, as far as I can tell.

• Is the use of caption really not recommended with the report class?
• If so, why and what should I do about it?
• If not, how can I 'tell' the package that mine is an 'ok class' to load with?

Answer 1

Perhaps not an answer, but it was too long to make it a comment. The documentation of the caption package says:

If you don’t find the document class you use in this section, you usually don’t have to worry: Many document classes (e.g. the octavo class) are derived from one of the standard document classes article, report, or book, and behave the same regarding captions. The caption package automatically does a compatibility check against the document class used and will give you the clear warning

Package caption Warning: Unsupported document class (or package)
detected, (caption) usage of the caption package is not recommended.
See the caption package documentation for explanation.

if such an incompatibility was detected. If you don’t get such warning everything is fine, but if you get it the usage of the caption package is not recommended and especially not supported.

If you get such a compatibility warning but decide to use the caption package anyway, you should watch carefully what side-effects occur, usually the look and feel of your captions will change by just including the caption package without options, meaning they do not look like as intended by the author of the document class. If this is fine for you, you should first specify the option style=base via \usepackage[style=base]{caption} or \captionsetup{style=base} to set the caption package into a well-defined state. Afterwards you can start setting your own options additionally and keep your fingers crossed.

Also, according to the documentation, the supported document classes are:

• Standard LaTeX: book, report, article
• AMS: amsart, amsproc, amsbook
• beamer
• KOMA-Script: scrreprt, scrartcl, scrbook
• NTG: artikel, rapport, boek
• SMF: smafart, smfbook
• thesis

So, there's no problem using caption with the standard report document class. Since you are using a derived document class, you should pay attention to the last paragraph of the quote at the beginning of this message.

Answer 2

One of your packages tries to load captions twice. I have the same issue because I'm loading the \subfig package, this blog post give an elegant solution:

Find the offending package and load it without the caption package.

\usepackage[caption=false]{subfig}

This has worked for me. It would really help though if you gave us your header and we could try and spot what was trying to load caption, and reduce the number of packages doing that to one.

Answer 3

Gonzalo's answer has explained why you can or can not include the caption package.

If you are sure you want to use it, and want to get rid of the warning, use

\usepackage{silence}
\WarningFilter{caption}{Unsupported document class}

Answer 4

A solution for this problem can be found here.

You can create in your project a file support-caption.sty

\setlength\abovecaptionskip{\f@size\p@}
\setlength\belowcaptionskip{0\p@}
\long\def\@makecaption#1#2{%
  \vskip\abovecaptionskip
  \sbox\@tempboxa{#1: #2}%
  \ifdim \wd\@tempboxa >\hsize
    #1: #2\par
  \else
    \global \@minipagefalse
    \hb@xt@\hsize{\hfil\box\@tempboxa\hfil}%
  \fi
  \vskip\belowcaptionskip}

Then, put in your preambule this:

\usepackage{support-caption}
\usepackage{subcaption}

Answer 5

You said

I had to get rid of subcaption (which it turns out I wasn't using anyways).

However, this is not true. subcaption loads caption anyway.

\ProvidesPackage{subcaption}[\caption@tempa v1.1-\caption@tempb Sub-captions (AR)]
\RequirePackage{caption}[2012/03/25] % needs v3.3 or newer

Indeed caption.sty and subcaption.sty are both part of the caption package.

This means that you can say

\usepackage{subcaption}

and will automatically have loaded caption also.

However, it doesn't matter if you also say

\usepackage{caption}

or

\usepackage[style=base]{caption}

Indeed, I cannot reproduce the warning you report using any combination of these lines in any order.

Nor do I get an error if I remove the line loading caption, provided I retain the line loading subcaption which itself loads caption.

Whatever the source of the conflicting definition in your files, it does not appear to be the use of subcaption in combination with caption. Indeed, it would be most peculiar were this the case, given that subcaption needs caption.