Error de matriz de paquete: token pream ilegal (\caption): `c' usado

Question

me encuentro con este error

Package array Error: Illegal pream-token (\caption): `c' used."

Por favor ayúdame a arreglarlo. Gracias

\documentclass[a4paper,11pt]{article}
\usepackage[english]{babel}
\usepackage[letterpaper,top=2cm,bottom=2cm,
   left=3cm,right=3cm,marginparwidth=1.75cm]{geometry}
\usepackage{amsmath}
\usepackage{longtable}
\usepackage{afterpage}
\usepackage{tabularx}
\usepackage{caption}
\usepackage{array}
\usepackage{graphicx}
\usepackage{makecell}
\afterpage{
\begin{longtable}[h!]
    \caption{Table 1: Features comparison} 
    \label{tab:my_label} \\
    \begin{tabularx}{\textwidth}{|%
    >{\centering\arraybackslash}X|>{\centering\arraybackslash}X|
    >{\centering\arraybackslash}X|>{\centering\arraybackslash}X|
    >{\centering\arraybackslash}X|>{\centering\arraybackslash}X|}
        \hline
        Authors &  Topic & Scalability & Comparison & Theoretical Value & Application\\
        \hline
        \cite{alzahrani2018detection}Alzahrani et al. 2018 & DDoS attack & No & No & No & \\
        \hline
        \cite{biggio2011support}Biggio et al. 2011 & Adversarial attack & No & No & No & \\
        \hline
        \cite{biggio2012poisoning}Biggio et al. 2012 & Poisoning attacks & No & No & No & \\
        \hline
        \cite{chen2018detecting}Chen et al. 2018 & Activation clustering & No & No & No & \\
        \hline
        \cite{fredrikson2015model}Fredrikson et al. 2015 & Inversion attacks & No & No & No & \\
        \hline
        \cite{fredrikson2014privacy}Fredrikson et al. 2014 & Inversion attacks & No & No & No & \\
        \hline
        \cite{goodfellow2014explaining}Goodfellow, et al. 2014 &  &  &  &  & \\
        \hline
        \cite{gu2017badnets}Gu, et al. 2017 &  &  &  &  & \\
        \hline
        \cite{hu2021artificial}Hu, et al. 2021 &  &  &  &  & \\
        \hline
        \cite{jaszcz2022aimm}Jaszc, et al. 2022 &  &  &  &  & \\
        \hline
        \cite{alzahrani2018detection}Alzahrani et al. 2018 & DDoS attack & No & No & No & \\
        \hline
        \cite{biggio2011support}Biggio et al. 2011 & Adversarial attack & No & No & No & \\
        \hline
        \cite{biggio2012poisoning}Biggio et al. 2012 & Poisoning attacks & No & No & No & \\
        \hline
        \cite{chen2018detecting}Chen et al. 2018 & Activation clustering & No & No & No & \\
        \hline
        \cite{fredrikson2015model}Fredrikson et al. 2015 & Inversion attacks & No & No & No & \\
        \hline
        \cite{fredrikson2014privacy}Fredrikson et al. 2014 & Inversion attacks & No & No & No & \\
        \hline
        \cite{goodfellow2014explaining}Goodfellow, et al. 2014 &  &  &  &  & \\
        \hline
        \cite{gu2017badnets}Gu, et al. 2017 &  &  &  &  & \\
        \hline
        \cite{hu2021artificial}Hu, et al. 2021 &  &  &  &  & \\
        \hline
        \cite{jaszcz2022aimm}Jaszc, et al. 2022 &  &  &  &  & \\
        \hline
    \end{tabularx}
\end{longtable}
}
\afterpage{
\bibliographystyle{splncs04}
\bibliography{splncs04}
}
\end{document} %This is the error location

Answer 1

No debes anidar un tabularxentorno dentro de unlongtable otro entorno. Además, dado que longtableno es un flotante (en el sentido específico de la palabra LaTeX), no tiene sentido proporcionar un especificador de posicionamiento como [h!].

Asumiré que lo que realmente quieres emplear es un xltabularentorno (proporcionado por elxtabularpaquete), que combina las capacidades delongtable y tabularxen unentorno único. Observa que xltabular, comotabularx , tomadosargumentos: (i) el ancho objetivo (aquí: \textwidth) y (ii) el grupo de especificaciones de columna.

\documentclass[a4paper,11pt]{article}
\usepackage[english]{babel}
\usepackage[letterpaper,vmargin=2cm,hmargin=3cm,
            marginparwidth=1.75cm]{geometry}
\usepackage{amsmath}
%\usepackage{longtable}
%\usepackage{tabularx}
%\usepackage{array}
\usepackage{xltabular}
\newcolumntype{C}{>{\centering\arraybackslash\hspace{0pt}}X}  % centered
\newcolumntype{L}{>{\raggedright\arraybackslash\hspace{0pt}}X}% left-aligned

\usepackage{caption}

\begin{document}
\setlength\extrarowheight{2pt} % for a less-cramped "look"

\begin{xltabular}{\textwidth}{|L|C|c|c|C|C|}

    % headers and footers
    \caption{Comparison of features} \label{tab:my_label} \\
    \hline
    Authors &  Topic & Scalability & Comparison & Theoretical Value & Application\\
    \hline
    \endfirsthead
    
    \multicolumn{6}{l}{\tablename\ \thetable, continued} \\[1ex]
    \hline
    Authors &  Topic & Scalability & Comparison & Theoretical Value & Application\\
    \hline
    \endhead
    
    \hline
    \multicolumn{6}{r}{\footnotesize (continued on next page)}\\
    \endfoot
    
    \endlastfoot
    
    
    % body of table
    \cite{alzahrani2018detection}Alzahrani et~al.\ 2018 & DDoS attack & No & No & No & \\
    \hline
    \cite{biggio2011support}Biggio et~al.\ 2011 & Adversarial attack & No & No & No & \\
    \hline
    \cite{biggio2012poisoning}Biggio et~al.\ 2012 & Poisoning attacks & No & No & No & \\
    \hline
    \cite{chen2018detecting}Chen et~al.\ 2018 & Activation clustering & No & No & No & \\
    \hline
    \cite{fredrikson2015model}Fredrikson et~al.\ 2015 & Inversion attacks & No & No & No & \\
    \hline
    \cite{fredrikson2014privacy}Fredrikson et~al.\ 2014 & Inversion attacks & No & No & No & \\
    \hline
    \cite{goodfellow2014explaining}Goodfellow et~al.\ 2014 & & & & & \\
    \hline
    \cite{gu2017badnets}Gu et~al.\ 2017 & & & & & \\
    \hline
    \cite{hu2021artificial}Hu et~al.\ 2021 & & & & & \\
    \hline
    \cite{jaszcz2022aimm}Jaszc et~al.\ 2022 & & & & & \\
    \hline
    \cite{alzahrani2018detection}Alzahrani et~al.\ 2018 & DDoS attack & No & No & No & \\
    \hline
    \cite{biggio2011support}Biggio et~al.\ 2011 & Adversarial attack & No & No & No & \\
    \hline
    \cite{biggio2012poisoning}Biggio et~al.\ 2012 & Poisoning attacks & No & No & No & \\
    \hline
    \cite{chen2018detecting}Chen et~al.\ 2018 & Activation clustering & No & No & No & \\
    \hline
    \cite{fredrikson2015model}Fredrikson et~al.\ 2015 & Inversion attacks & No & No & No & \\
    \hline
    \cite{fredrikson2014privacy}Fredrikson et~al.\ 2014 & Inversion attacks & No & No & No & \\
    \hline
    \cite{goodfellow2014explaining}Goodfellow et~al.\ 2014 & & & & & \\
    \hline
    \cite{gu2017badnets}Gu et~al.\ 2017 & & & & & \\
    \hline
    \cite{hu2021artificial}Hu et~al.\ 2021 & & & & & \\
    \hline
    \cite{jaszcz2022aimm}Jaszc et~al.\ 2022 & & & & & \\
    \hline

\end{xltabular}

\end{document}