Centering in a table

Question

\documentclass{article}    
\begin{document}

 \begin{center}
    \begin{tabular}{ | p{5cm} | p{5cm} | p{7cm} |}\hline

\centering{A} &     
\centering{B} &     
\centering{C} \\ \hline

\end{tabular} 
\end{center}

\end{document}

I am making an A4 document and I want the words in the first row of the table to be centered. Here I have omitted other rows. But errors occur and it seems that I can't use \centering for the last column. Why doesn't it work?

Answer 1

With the width of the tabular exceeding 17cm, the margins have to be quite narrow if the material is supposed to fit inside the textblock. In the example below, the margins are set to 1cm. (Aside: rather than setting puny margins, I'd reduce the column widths in the tabular.)

\documentclass{article}    
\usepackage[a4paper,margin=1cm]{geometry}
\usepackage{lipsum}  % filler text
\begin{document}

\hrule %% just to illustrate width of text block

\begin{center}
\begin{tabular}{ | p{5cm} | p{5cm} | p{7cm} |}
\hline
\multicolumn{1}{|c}{A} & \multicolumn{1}{|c}{B} & \multicolumn{1}{|c|}{C} \\ 
\hline
\lipsum*[2] & \lipsum*[2] & \lipsum*[2] \\
\hline
\end{tabular} 
\end{center}

\end{document}