Aligning top row of a table with the item label in a list

Question

I have used the enumerate environment to create a list in which every item contains a table, created using the tabular environment. The first row of each table should be aligned with the item label, (a), (b), etc. This is not the the case if the table starts with an \hline. How can I fix the alignment in such a case?

\documentclass{article}
\usepackage{enumerate} 
\begin{document}
\begin{enumerate}[(a)]
\item 
   \begin{tabular}[t]{|c|c|}
     a & b \\  \hline c & d  \\ \hline
   \end{tabular}
\item 
   \begin{tabular}[t]{|c|c|} 
     \hline e & f \\ \hline g & h \\ \hline
   \end{tabular}
\end{enumerate}
\end{document}

Answer 1

I just had to solve this problem, and "The LaTeX Companion" (second edition) has the answer on page 280. The [t] option aligns the tabular to the \hline instead of the baseline of the text. The array package has the command \firsthline which corrects this:

\documentclass{article}
\usepackage{enumerate,array} 
\begin{document}
\begin{enumerate}[(a)]
\item 
   \begin{tabular}[t]{|c|c|}
     a & b \\  \hline c & d  \\ \hline
   \end{tabular}
\item 
   \begin{tabular}[t]{|c|c|} 
     \firsthline e & f \\ \hline g & h \\ \hline
   \end{tabular}
\end{enumerate}
\end{document}

This is the result:

Answer 2

With {NiceTabular} of nicematrix, you will directly have the expected output.

\documentclass{article}
\usepackage{nicematrix}
\usepackage{enumerate} 
\begin{document}

\begin{enumerate}[(a)]
\item 
   \begin{NiceTabular}[t]{|c|c|}
     a & b \\  \hline c & d  \\ \hline
   \end{NiceTabular}
\item 
   \begin{NiceTabular}[t]{|c|c|} 
     \hline e & f \\ \hline g & h \\ \hline
   \end{NiceTabular}
\end{enumerate}

\end{document}

You need several compilations (because nicematrix uses PGF/Tikz nodes under the hood).

Answer 3

i don't know what is the cause of your problem, however work around can be use \fbox instead top/bottom (and vertical outer lines too) table's \hline:

\documentclass{article}
\usepackage{enumerate}
\newcommand\tabbox[1]{\setlength\fboxsep{0pt}\fbox{#1}} % <-- new

\begin{document}
\begin{enumerate}[(a)]
\item
   \begin{tabular}[t]{|c|c|}
     a & b \\  \hline c & d  \\ \hline
   \end{tabular}
\item
   \tabbox{\begin{tabular}[t]{c|c} % <-- new
            e & f \\ \hline g & h \\
           \end{tabular}}
\end{enumerate}
\end{document}