overlapping in footer, try tabularx in footer

Question

I have a document (twopage) in which the left field is overlapping with the middle field. One solution is to put an \hspace{...} before the middle field but works for odd pages only. I'm trying to setup a tabularx. (tabular is crashing)

here is my MWE, the first part is with tabularx (its width does not do what specified) and the second part is with the \hspace

\documentclass[a4paper,twoside]{article}
\usepackage{lipsum,fancyhdr,tabularx,tabularray}

\pagestyle{fancy}
\fancyhf{}
\fancyhead[C]{\textbf{entête}}

\fancyfoot[CO]{%
  \begin{tabularx}{\textwidth}{@{}c|c|c@{}}
    here is the title of the chapter, sometime long  & book title & \thepage \tabularnewline
  \end{tabularx}
}

\fancyfoot[CE]{%
  \begin{tabularx}{\textwidth}{@{}c|c|c@{}}
    \thepage & book title & here is the title of the chapter, sometime long \tabularnewline
  \end{tabularx}
}
\begin{document}
  \lipsum{1}
  \newpage

\fancyfoot[C]{%
 \hspace{20em}book title 
}

\fancyfoot[LO,RE]{%
  here is the title of the chapter, sometimes long
}

\fancyfoot[RO,LE]{%
  \thepage
}

  \lipsum{2} 
\end{document}

Answer 1

Here are two options:

1. Spread out the footer content evenly (using \hfills).

2. Limit the possibly-long chapter title to 50% of the footer width, aligning it vertically to the baseline.

\documentclass[twoside]{article}

\usepackage{lipsum,fancyhdr}

\pagestyle{fancy}

\begin{document}

% Page style option 1: evenly spread left/center/right footer
\fancyhf{}% Clear header/footer
\fancyhead[C]{Centre header}

\fancyfoot[CO]{%
  A here is the title of the chapter, sometime long\hfill
  book title\hfill
  \thepage
}

\fancyfoot[CE]{%
  \thepage\hfill
  book title
  \hfill
  B here is the title of the chapter, sometime long
}

\lipsum[1-10]

\clearpage

% Page style option 2: Limit chapter title to 50% of footer width (bottom-aligned)
\fancyhf{}% Clear header/footer
\fancyhead[C]{Centre header}

\fancyfoot[CO]{%
  \parbox[b]{0.5\linewidth}{\raggedright A here is the title of the chapter, sometime long}\hfill
  book title\hfill
  \thepage
}

\fancyfoot[CE]{%
  \thepage\hfill
  book title
  \hfill
  \parbox[b]{0.5\linewidth}{\raggedleft B here is the title of the chapter, sometime long}
}

\lipsum[1-10]

\end{document}

Note that in both cases only the Centre footer element is used, which is placed in a box that spans the text width.

Here is the output of the first option:

A drawback of this option is that varying lengths of a chapter title (or page number width) will have the layout seem to change, as the gap is just filled with stretch (whatever is needed).

Here is the output of the second option:

A drawback of this option might be that there is mis-alignment (visually) with a too-short title - something that doesn't fill 50% of the footer width.

My recommendation is to provide an alternative, shorter title to avoid the overlap to begin with. Moreover, consider spreading the content to the header as well (further avoiding overlap opportunities).

Answer 2

The issue is simple: fancyhdr has done exactly what you asked:

\fancyfoot[C]{%
  \hspace{20em}book title 
}

20em is not a fixed width because it is font-dependent, but, in most cases, it is a significant chunk of the width of the text block. To see what is happening, just add x before the space,

\fancyfoot[C]{%
 x\hspace{20em}book title 
}

Exactly the same happens on odd pages, but the result happens not to be overlapping text.

So if you want to use long titles rather than shortened versions in the footers, you do need something other than the tripartite division provided by fancyhdr. To avoid that, you could tweak your hack to put the \hspace in the right place.

\fancyfoot[CO]{%
 \hspace{20em}book title%
}
\fancyfoot[CE]{%
  book title\hspace{20em}%
}

Alternatively, you could use a tabularx setup with or without fancyhdr's assistance. It's hard to think what alignment you have in mind here, but perhaps something like the following, which assumes the title is never so long as to run to a second line,

\fancyfoot[CO]{%
  \begin{tabularx}{\textwidth}{@{}l|>{\centering}X|r@{}}
    here is the title of the chapter, sometime long  & book title & \thepage \tabularnewline
  \end{tabularx}%
}

\fancyfoot[CE]{%
  \begin{tabularx}{\textwidth}{@{}l|>{\centering}X|r@{}}
    \thepage & book title & here is the title of the chapter, sometime long \tabularnewline
  \end{tabularx}%
}

As David explained, any tabularx must include at least one X column.

If the title might run to a second line, you need to allow for that and that means the chapter needs an/the X, which makes alignment trickier. In that case you really don't want vertical rules (which I wouldn't use anyway, but nobody would use them here), so maybe something like

\fancyfoot[CO]{%
  \begin{tabularx}{\textwidth}{@{}Xcr@{}}
    here is the title of the chapter, sometimes ridiculously, absurdly, incredibly, magnificently long  & book title & \hspace*{10mm}\thepage \tabularnewline
  \end{tabularx}%
}

\fancyfoot[CE]{%
  \begin{tabularx}{\textwidth}{@{}lc>{\raggedleft}X@{}}
    \thepage\hspace*{10mm} & book title & here is the title of the chapter, sometimes ridiculously, absurdly, incredibly, magnificently long \tabularnewline
  \end{tabularx}%
}

Or you could use tabular* rather than tabularx, as David also suggested.

I would post images, but I can't crop multipage output and conversion takes a significant amount of time and insists on converting all pages, so you'll have to compile and/or run them for yourself as Okular still haven't fixed the bug on X.