Wordpress - post thumbnail in loop - php

Question

So I'd like to add a thumbnail to my posts but I just can't get it to work.
<?php get_header(); ?>
<div id="main-content">
<?php get_sidebar(); ?>
<?php
$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
query_posts('posts_per_page=3&paged=' . $paged);
?>
<?php if (have_posts()) : while ( have_posts()) : the_post(); ?>
<div <?php post_class() ?> id="post-<?php the_ID(); ?>">
<h2><?php the_title(); ?></h2>
<?php the_post_thumbnail();?>
<div class="entry">
<?php the_excerpt(); ?>
<a class="read-more" href="<?php the_permalink() ?>">Read More ...</a>
</div>
<?php include (TEMPLATEPATH . '/inc/meta.php' ); ?>
<div class="postmetadata">
<?php the_tags('Tags: ', ', ', '<br />'); ?>
Posted in <?php the_category(', ') ?> |
<?php comments_popup_link('No Comments »', '1 Comment »', '% Comments »'); ?>
</div>
</div>
<?php endwhile; endif; ?>
<div class="navigation">
<div class="next-posts"><?php next_posts_link('« Older Posts') ?></div>
<div class="prev-posts"><?php previous_posts_link('Newer Posts »') ?></div>
</div>
</div>
<!-- end div main-content -->
<?php get_footer(); ?>
And in my functions.php I've added - add_theme_support('post-thumbnails');
It gives me the option to post the thumbnail when I make a post, but it doesn't show up.

Answer 1

What theme or parent theme are you using? I usually do something like this inside the loop:
<?php
if ( function_exists( 'add_image_size' ) ) {
add_image_size( 'custom-thumb', 180, 115, true ); //add a custom image size
}
echo get_the_post_thumbnail(get_the_ID(), 'custom-thumb', $attr); //echo the thumbnail with the new custom image size
?>

Answer 2

<?php
if ( has_post_thumbnail() ) { // check if the post has a Post Thumbnail assigned to it.
the_post_thumbnail();
}
?>
Add the above code in loop
Then add the following code to functions.php
add_theme_support( 'post-thumbnails' );
Then at last, if you wish to link your thumbnail to post id, so your posts opens after clicking image, add the following code to functions.php
set_post_thumbnail_size( 50, 50 );
add_filter( 'post_thumbnail_html', 'my_post_image_html', 10, 3 );
function my_post_image_html( $html, $post_id, $post_image_id ) {
$html = '' . $html . '';
return $html;
}
set_post_thumbnail_size( height, width); this is used to add height and width, in above example i added 50, 50. Change it with your required value

Answer 3

with the new wordpress versions you can setup thumbnails from settings > media . and give the personnal size to thumbnail Then use this to get the thumbnail with your prefered size
<?php the_post_thumbnail('thumbnail');?>