How does \thanks work in LaTeX article class?

Question

I am trying to figure out how it happens that \thanks in the standard LaTeX article class (with no options specified) is typeset with an asterisk for the footnote mark.

I got lost trying to trace the definitions and redefinitions of \@thanks and \footnotemark and \c@footnote through article.cls and latex.ltx. I also tried grepping all the LaTeX base files for \\ast, thinking that this must be used somewhere to redefine the footnote mark, but I couldn't find anything.

(This question came up because I would like to convert the \thanks footnote to an endnote for journal submission, but my question is about the mechanics of this command.)

MWE:

\documentclass{article}
\begin{document}
\title{Example}
\author{Name\thanks{Affiliation, e-mail}}
\maketitle
\end{document}

Here's what I have been able to figure out:

The definition of \maketitle in article.cls:

\newcommand\maketitle{\par                                                                     
  \begingroup                                                                                  
    \renewcommand\thefootnote{\@fnsymbol\c@footnote}%                                          
    \def\@makefnmark{\rlap{\@textsuperscript{\normalfont\@thefnmark}}}%                        
    \long\def\@makefntext##1{\parindent 1em\noindent                                           
            \hb@[email protected]{%                                                                     
                \hss\@textsuperscript{\normalfont\@thefnmark}}##1}%                            
    \if@twocolumn                                                                              
      \ifnum \col@number=\@ne                                                                  
        \@maketitle                                                                            
      \else                                                                                    
        \twocolumn[\@maketitle]%                                                               
      \fi                                                                                      
    \else                                                                                      
      \newpage                                                                                 
      \global\@topnum\z@   % Prevents figures from going at top of page.                       
      \@maketitle                                                                              
    \fi                                                                                        
    \thispagestyle{plain}\@thanks                                                              
  \endgroup                                                                                    
  \setcounter{footnote}{0}%                                                                    
  \global\let\thanks\relax                                                                     
  \global\let\maketitle\relax                                                                  
  \global\let\@maketitle\relax                                                                 
  \global\let\@thanks\@empty                                                                   
  \global\let\@author\@empty                                                                   
  \global\let\@date\@empty                                                                     
  \global\let\@title\@empty                                                                    
  \global\let\title\relax                                                                      
  \global\let\author\relax                                                                     
  \global\let\date\relax                                                                       
  \global\let\and\relax                                                                        
}

I see that the footnotemark is redefined in some way, and that \@thanks is called at the end. But \thanks and \@thanks are not defined in this file.

Here are the definitions of \thanks and \@thanks in latex.ltx:

\def\thanks#1{\footnotemark                                                                    
    \protected@xdef\@thanks{\@thanks                                                           
        \protect\footnotetext[\the\c@footnote]{#1}}%                                           
}                                                                                              
\let\@thanks\@empty

It seems like \thanks redefines \@thanks to be \@thanks plus a footnote containing its argument. It looks like \thec@footnote would produce the value of a footnote counter and typeset a numeral, not an asterisk. The article class calls \@thefnmark in \maketitle but never redefines it to an asterisk (that I can tell).

Answer 1

Let's look at some definitions:

• \thanks within article.cls:

  \def\thanks#1{\footnotemark
      \protected@xdef\@thanks{\@thanks
          \protect\footnotetext[\the\c@footnote]{#1}}%
  }
  

  This macro sets a footnote mark - \footnotemark. Then it adds the footnote text to \@thanks using \protected@xdef\@thanks{\@thanks <new footnote text>}.

• \maketitle in article.cls:

  \newcommand\maketitle{\par
    \begingroup
      \renewcommand\thefootnote{\@fnsymbol\c@footnote}%
      \def\@makefnmark{\rlap{\@textsuperscript{\normalfont\@thefnmark}}}%
      \long\def\@makefntext##1{\parindent 1em\noindent
              \hb@[email protected]{%
                  \hss\@textsuperscript{\normalfont\@thefnmark}}##1}%
      \if@twocolumn
        \ifnum \col@number=\@ne
          \@maketitle
        \else
          \twocolumn[\@maketitle]%
        \fi
      \else
        \newpage
        \global\@topnum\z@   % Prevents figures from going at top of page.
        \@maketitle
      \fi
      \thispagestyle{plain}\@thanks
    \endgroup
    \setcounter{footnote}{0}%
    \global\let\thanks\relax
    \global\let\maketitle\relax
    \global\let\@maketitle\relax
    \global\let\@thanks\@empty
    \global\let\@author\@empty
    \global\let\@date\@empty
    \global\let\@title\@empty
    \global\let\title\relax
    \global\let\author\relax
    \global\let\date\relax
    \global\let\and\relax
  }
  

  Inside \maketitle, a number of redefinitions of the footnote mechanism occurs within a group \begingroup...\endgroup.

  Firstly, the footnote numbering is changed to \@fnsymbol - the regular *, †, ‡, §, ¶, ‖, **, ††, ‡‡, (error) sequence:

  \def\@fnsymbol#1{\ensuremath{\ifcase#1\or *\or \dagger\or \ddagger\or
     \mathsection\or \mathparagraph\or \|\or **\or \dagger\dagger
     \or \ddagger\ddagger \else\@ctrerr\fi}}
  

  Secondly, an update is made to the way the footnote mark and text is set - that is, the macros \@makefnmark and \@makefntext are updated. These updates (redefinitions) are very minimal in the sense that they really are very similar to the original definitions outside the \maketitle usage (also taken from latex.ltx:

  % From latex.ltx
  \def\@makefnmark{\hbox{\@textsuperscript{\normalfont\@thefnmark}}}
  % From article.cls
  \newcommand\@makefntext[1]{%
      \parindent 1em%
      \noindent
      \hb@[email protected]{\hss\@makefnmark}#1}
  

  The only major difference is that the footnote mark is set using \rlap. This is because within the list of \authors, you'd typically separate with a ,, for which this redefinition allows the footnote mark to overlap with.

  Thirdly the actual title is set using \@maketitle:

  \def\@maketitle{%
    \newpage
    \null
    \vskip 2em%
    \begin{center}%
    \let \footnote \thanks
      {\LARGE \@title \par}%
      \vskip 1.5em%
      {\large
        \lineskip .5em%
        \begin{tabular}[t]{c}%
          \@author
        \end{tabular}\par}%
      \vskip 1em%
      {\large \@date}%
    \end{center}%
    \par
    \vskip 1.5em}
  

  The setting of the \thanks marks (footnote marks) as well as the collection into \@thanks occurs with the setting of \@author.

  Finally, at the end of \maketitle, \@thanks is called, which "releases" the accumulated footnote texts collected with \@author.

  Since \@thanks carries content globally (due to \protected@xdef), it's cleared at the end of \maketitle (outside the \begingroup...\endgroup scope), together with other macros.

Now let's look at an example:

\documentclass{article}
\usepackage[paperheight=20\baselineskip]{geometry}% Just for this example
\title{Some title}
\author{Author1\thanks{Abc}, Author2\thanks{Def} and Author3\thanks{Ghi}}
\begin{document}
\maketitle
\end{document}

• Note how the overlapping occurs of the footnote marks with the punctuation after Author1.

• With the addition of

  \usepackage{etoolbox}
  \makeatletter
  % \patchcmd{<cmd>}{<search>}{<replace>}{<success>}{<failure>}
  \patchcmd{\@maketitle}{\@author}{\@author\show\@thanks}{}{}
  \makeatother
  

  to the preamble we can see the .log outputs the sequence of accumulate footnote texts stemming from the \thanks inside \@author:

  > \@thanks=macro:
  ->\protect \footnotetext [1]{Abc}\protect \footnotetext [2]{Def}\protect \footn
  otetext [3]{Ghi}.
  \@maketitle ...ular}[t]{c}\@author \show \@thanks 
                                                    \end {tabular}\par }\vskip...
  l.11     \maketitle
  

  These are set immediately at the end of \maketitle as mentioned above.