Check what kind of document class is used with MWE

Question

I try to autodefine the preamble using this and that approach but do get Undefined control sequence. \@ifundefined{\KOMAClassName } in case I write report for scrreprt. for both options.

\documentclass[12pt,a4paper,notitlepage,oneside]{report}
%NOTE Packages, my Macros und Formatdefinitions
    \usepackage[T1]{fontenc}            % Allows different font encodings and hyphenation -> ctan.org/pkg/fontenc
    \usepackage[utf8]{inputenc}         % Translates input encodings into LaTeX internal language -> ctan.org/pkg/inputenc
    \usepackage{blindtext}
    \makeatletter
        \@ifundefined{KOMAClassName }{\newcommand{\test}{num1} }{\newcommand{\test}{num2} } %option1
        \@ifclassloaded{KOMAClassName }{\newcommand{\testb}{num1} }{\newcommand{\testb}{num2} } %option2
    \makeatother
\begin{document}
\section{hi}
\test \\
\testb\\
\end{document}

Using scrreprt or report I get printed num1 and num2 for \test and \testb (which isnt also the case)

Answer 1

Use \@ifundefined{KOMAClassName}{...}{...} since \@ifundefined calls

\expandafter\ifx\csname #1 \endcsname (after a test), i.e. it constructs the command sequence.

Here's the definition in latex.ltx.

\def\@ifundefined#1{%
  \expandafter\ifx\csname#1\endcsname\relax
    \expandafter\@firstoftwo
  \else
    \expandafter\@secondoftwo
  \fi}

But for \@ifclassloaded you need the class name, i.e. what \KOMAClassName provides for you.

The difference between the commands is just that \@ifundefined checks for a command name comparing it with \relax whereas \@ifclassloaded checks for a token, i.e. a class name. KOMAClassName means a class named KOMAClassName and not what \KOMAClassName provides (scrreprt, expectedly?)

I am not sure what the \test and \testb commands should do, but I think the setup should be something like

\documentclass[12pt,a4paper,notitlepage,oneside]{scrreprt}
%NOTE Packages, my Macros und Formatdefinitions
    \usepackage[T1]{fontenc}            % Allows different font encodings and hyphenation -> ctan.org/pkg/fontenc
    \usepackage[utf8]{inputenc}         % Translates input encodings into LaTeX internal language -> ctan.org/pkg/inputenc
    \usepackage{blindtext}
%    \providecommand{\test}{}
%    \providecommand{\testb{}
    \newif\ifstandardreport
    \makeatletter
    \@ifundefined{KOMAClassName}{%
      \standardreporttrue
      \newcommand{\test}{num1} 
    }{%
      \newcommand{\test}{num2}  %option1
    }
    \ifstandardreport
    \newcommand{\testb}{num1} 
    \else
    \@ifclassloaded{\KOMAClassName}{%
      \newcommand{\testb}{num2}
    }{
      \newcommand{\testb}{num1} 
    } %option2
    \fi
    \makeatother
\begin{document}
\section{hi}
\test \\
\testb\\
\end{document}

Alternatively use \providecommand{\test}{...} and do \renewcommand{\test}{...} later on in the \@ifclassloaded tests.

Answer 2

\KOMAClassName can be used to test if a KOMA-class is used, as they all define that command. It cannot be used to test for a special class.

\documentclass[12pt,a4paper,notitlepage,oneside]{scrartcl}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{blindtext}
\makeatletter
\@ifundefined{KOMAClassName}{%
    \typeout{A standard class is used, but which one?}
    \@ifclassloaded{article}{%
        \typeout{This is an article document}
    }{%
        \@ifclassloaded{report}{%
            \typeout{This is a report document}
        }{%
            \@ifclassloaded{book}{%
                \typeout{This is a book document}
            }{%
                \@ifclassloaded{memoir}{%
                    \typeout{Memoir is in use}
                }{%
                    \typeout{Something else is going on}
                }
            }
        }
    }
}{%
        \typeout{A KOMA class is used, but which one?}
        \@ifclassloaded{scrartcl}{\typeout{scrartcl is used}
    }{%
        \@ifclassloaded{scrreprt}{%
            \typeout{scrreprt is used}
        }{%
            \@ifclassloaded{scrbook}{scrbook is loaded}{\typeout{Something else is going on}
            \@ifclassloaded{memoir}{\typeout{Memoir? In this branch? Impossible}
        }{}
    }
}
}
}
\@ifclassloaded{KOMAClassName}{\typeout{Wait? What?}}{\typeout{There is no class with that name}}
\makeatother
\begin{document}
Wombat
\end{document}