How to get cat ID in query_posts in single.php

What is it that you’re trying to do, exactly?

A little clarification might help us give you an answer.

I want to list some posts outside the loop in single post page, i’m using query_posts to that, and i want the posts to be the same category, in archives pages the code i’ve used works, but for single posts pages it doesnt work..
maybe the cat='.get_query_var('cat') is wrong

Don’t know where I first saw (or used this) but, it will display posts belonging to the categories of the current post without duplicating the current post

<?php
global $post;
$cat_ID=array();
$categories = get_the_category(); //get all categories for this post
  foreach($categories as $category) {
    array_push($cat_ID,$category->cat_ID);
  }
  $args = array(
  'orderby' => 'date',
  'order' => 'DESC',
	'post_type' => 'post',
	'numberposts' => 8,
	'post__not_in' => array($post->ID),
	'category__in' => $cat_ID
  ); // post__not_in will exclude the post we are displaying
    $cat_posts = get_posts($args);
    $out='';
      foreach($cat_posts as $cat_post) {
          $out .= '<li>';
          $out .=  '<a href="'.get_permalink($cat_post->ID).'" title="'.wptexturize($cat_post->post_title).'">'.wptexturize($cat_post->post_title).'</a></li>';
      }
    $out = '<ul class="cat_post">' . $out . '</ul>';
    echo $out;
?>

im using this

<?php
		query_posts('showposts=8&amp;cat='.get_query_var('cat')); ?>
<?php if (have_posts()) : while (have_posts()) : the_post(); ?>
<div class="postt">
			<a target="_blank" href="/link/out.php?link=gal&amp;s=80&amp;url=<?php the_permalink() ?>" rel="bookmark" title="<?php printf(__('Permanent Link to %s', 'mandigo'), the_title('', '', false)); ?>">
<?php global $more; $more = FALSE; ?>
<?php the_content(''); ?>
<?php $more = TRUE; ?><b><?php the_title(); ?></b></a></div>
<?php endwhile; endif; ?>

but it dont get the category id correctly in single post page :/

Well I don’t believe get_query_var('cat') will work in single.php.

dont have anything simple like and that works?

Not really, it’s more complex with a single post because you have to get the categories (there could be more than one) for the post.

getting just the first category will work

$categories = get_the_category(); //get all categories for this post
echo ‘first category is ‘ . $categories[0]->cat_ID;