$qv['cat'] = preg_replace( '|[^0-9,-]|', '', $qv['cat'] );

$mycategory=get_category_by_slug('a-category-slug');
$args = array( 'posts_per_page' => -1, 'category' => $mycategory);
$myposts = get_posts( $args );

$mycategory=get_category_by_slug('a-category-slug');
$args = array( 'posts_per_page' => -1, 'category' => $mycategory->term_id);
$myposts = get_posts( $args );