Tabular gets aligned to the right for no obvious reason

Question

I have a tabular which gets aligned to the right while I use \centering. I'm using the article class with only the packages babel and array. The code I have:

\documentclass[paper=a4]{article} % A4 paper and 11pt font size
\usepackage[dutch]{babel} % Dutch language/hyphenation

\usepackage{array}
\newcolumntype{+}{>{\global\let\currentrowstyle\relax}}
\newcolumntype{^}{>{\currentrowstyle}}
\newcommand{\rowstyle}[1]{\gdef\currentrowstyle{#1}%
#1\ignorespaces
}
\newcolumntype{C}[1]{>{\centering\arraybackslash}m{#1}}

\begin{document}

\begin{table}[h]
\newcommand\colwidth{10pt}
\let\oldmulticolumn\multicolumn
\renewcommand\multicolumn[3]{\oldmulticolumn{#1}{#2}{\textrm{#3}}}
\centering
\texttt{
\begin{tabular}{+r || ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} || ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} || ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} || ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} ||}
    \rowstyle{\normalfont}
                & 15 & 14 & 13 & 12 & 11 & 10 & 9 & 8 & 7 & 6 & 5 & 4 & 3 & 2 & 1 & 0 \\\hline
    LOADHI      & \multicolumn{3}{c|}{dest} & 0 & \multicolumn{4}{c||}{const} & \multicolumn{4}{c||}{const} & \multicolumn{4}{c||}{const} \\\cline{6-9}
    LOADLO      & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 1 & \multicolumn{4}{c||}{const} & \multicolumn{4}{c||}{const} \\\hline
    ALUf        & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 0 & 1 & \multicolumn{3}{c||}{addr. A} & 1 & \multicolumn{3}{c||}{opcode} \\
    ALU         & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 0 & 0 & \multicolumn{3}{c||}{addr. A} & 1 & \multicolumn{3}{c||}{opcode} \\\cline{10-13}
    ALU         & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 0 & \multicolumn{4}{c||}{const. A} & 0 & \multicolumn{3}{c||}{opcode} \\\hline
    READ        & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 0 & 1 & \multicolumn{3}{c||}{addr. A} & 1 & 1 & 1 & 1 \\\cline{10-13}
    READ        & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 0 & \multicolumn{4}{c||}{const. A} & 0 & 1 & 1 & 1 \\\cline{2-5}\cline{10-13}
    WRITE       & 0 & 0 & 0 & 0 & \multicolumn{3}{c|}{addr. B} & 0 &  & \multicolumn{3}{c||}{addr. A} & 1 &  &  & \\\hline
    COND\_CHK   & 0 & 0 & 0 & 0 &  &  &  & 1 &  &  &  &  & \multicolumn{4}{c||}{condition}\\\hline
\end{tabular}
}
\caption{Instruction set}
\end{table}

\end{document}

The table may be a bit complicated on the inside, but I don't see why it should get aligned to the right, like here. The grey sides are the ends of the document. You can clearly see the caption is centered, but the tabular is not.

Why is that and how can I fix it?

Answer 1

You need to make the table narrower than the text width, also as latex warns:

LaTeX Warning: Unused global option(s):
    [paper=a4].

The document class option syntax was wrong.

\documentclass[a4paper]{article} % A4 paper and 11pt font size
\usepackage[dutch]{babel} % Dutch language/hyphenation

\usepackage{array}
\newcolumntype{+}{>{\global\let\currentrowstyle\relax}}
\newcolumntype{^}{>{\currentrowstyle}}
\newcommand{\rowstyle}[1]{\gdef\currentrowstyle{#1}%
#1\ignorespaces
}
\newcolumntype{C}[1]{>{\centering\arraybackslash}m{#1}}

\begin{document}

\begin{table}[htp]

\noindent X\dotfill X
\newcommand\colwidth{9pt}

\setlength\tabcolsep{3pt}
\let\oldmulticolumn\multicolumn
\renewcommand\multicolumn[3]{\oldmulticolumn{#1}{#2}{\textrm{#3}}}
\centering\small
\texttt{%
\begin{tabular}{+r || ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} || ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} || ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} || ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} | ^C{\colwidth} ||}
    \rowstyle{\normalfont}
                & 15 & 14 & 13 & 12 & 11 & 10 & 9 & 8 & 7 & 6 & 5 & 4 & 3 & 2 & 1 & 0 \\\hline
    LOADHI      & \multicolumn{3}{c|}{dest} & 0 & \multicolumn{4}{c||}{const} & \multicolumn{4}{c||}{const} & \multicolumn{4}{c||}{const} \\\cline{6-9}
    LOADLO      & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 1 & \multicolumn{4}{c||}{const} & \multicolumn{4}{c||}{const} \\\hline
    ALUf        & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 0 & 1 & \multicolumn{3}{c||}{addr. A} & 1 & \multicolumn{3}{c||}{opcode} \\
    ALU         & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 0 & 0 & \multicolumn{3}{c||}{addr. A} & 1 & \multicolumn{3}{c||}{opcode} \\\cline{10-13}
    ALU         & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 0 & \multicolumn{4}{c||}{const. A} & 0 & \multicolumn{3}{c||}{opcode} \\\hline
    READ        & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 0 & 1 & \multicolumn{3}{c||}{addr. A} & 1 & 1 & 1 & 1 \\\cline{10-13}
    READ        & \multicolumn{3}{c|}{dest} & 1 & \multicolumn{3}{c|}{addr. B} & 0 & \multicolumn{4}{c||}{const. A} & 0 & 1 & 1 & 1 \\\cline{2-5}\cline{10-13}
    WRITE       & 0 & 0 & 0 & 0 & \multicolumn{3}{c|}{addr. B} & 0 &  & \multicolumn{3}{c||}{addr. A} & 1 &  &  & \\\hline
    COND\_CHK   & 0 & 0 & 0 & 0 &  &  &  & 1 &  &  &  &  & \multicolumn{4}{c||}{condition}\\\hline
\end{tabular}%
}
\caption{Instruction set}
\end{table}

\end{document}