How to limit author related post listing ?

Question

The solution <?php query_posts('posts_per_page=9'); ?> to limit author related posts show the entire website post :(

  <?php
    $curauth = (isset($_GET['author_name'])) ? get_user_by('slug', $author_name) : get_userdata(intval($author));
  ?>
  <h2>About: <?php echo $curauth->nickname; ?></h2>
  <dl>
    <dt>Website</dt>
    <dd><a href="<?php echo $curauth->user_url; ?>"><?php echo $curauth->user_url; ?></a></dd>
    <dt>Profile</dt>
    <dd>
      <?php echo $curauth->user_description; ?>
    </dd>
  </dl>

  <h2>Posts by <?php echo $curauth->nickname; ?>:</h2>

  <ul>
    <?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
      <li>
        <a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link: <?php the_title(); ?>">
          <?php the_title(); ?>
        </a>,
        <?php the_time('d M Y'); ?> in
          <?php the_category('&');?>
      </li>

      <?php endwhile; else: ?>
        <p>
          <?php _e('No posts by this author.'); ?>
        </p>    
      <?php endif; ?>
  </ul>

Answer 1

Never, never re-query a native archive - use the pre_get_posts hook to alter the main query:

add_action( 'pre_get_posts', function ( $wp_query ) {
    if ( $wp_query->is_main_query() && $wp_query->is_author() ) {
        $paged = max( 1, ( int ) $wp_query->get( 'paged' ) );

        if ( $paged === 1 ) {
            $wp_query->set( 'posts_per_page', 10 );
        } else {
            $wp_query->set( 'posts_per_page', 9 );
            $wp_query->set( 'offset', ( ( $paged - 1 ) * 9 ) + 1 );
        }
    }
});

Add the above to your functions.php and remove query_posts( ... ) line.

Answer 2

To create secondary listings (for example, a list of related posts at the bottom of the page, or a list of links in a sidebar widget), try making a new instance of WP_Query or use get_posts().

Why ? query_posts() is meant for altering the main loop. It does so by replacing the query used to generate the main loop content.

Infos from developer.wordpress.org query_posts()

SO in your code, you'll need to create a new query,

$related_query = get_posts(array(
                     'post_type'=> 'post',
                     'post_status'=> 'publish',
                     'post_author'=> $curauth,// must be the id
                     'posts_er_page'=> 9,  
                     )
);
if ( $related_query ) {
foreach ( $related_query as $post ) :
    setup_postdata( $post ); ?>
    <h2><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
    <?php the_content(); ?>
    <?php
    endforeach; 
    wp_reset_postdata();
}