Horizontal line for two column

Question

I have

\documentclass[twocolumn]{article}

\begin{document}
\rule{\textwidth}{1pt}
\end{document}

However, this line crosses the two columns. I just want the line cross the first column.

Answer 1

Use \linewidth for the width of the current environment (in this case, the current column). Use \textwidth for the width of the whole text block on the page.