Unable to display the post thumbnail in the loop

Question

I am trying to create a blog-listing page, that'll display the title and the featured images. Here's the loop that I am using

page.php

<div class="p-5 container" style="text-align:center;">
    <h1 style="margin-bottom:5vh;font-weight:bold;">Latest Posts</h1>
    <section class="thumbnails row">
    <?php $wpdb = new WP_Query(array(
            'post_type'=>'post',
            // 'post_type'       => 'publish',
            'post_status' => 'any',
            'posts_per_page' => 10));

            if($wpdb->have_posts()):
                while($wpdb->have_posts()):
                    $wpdb->the_post();?>
            <?php
            get_template_part('blog-show');
                // echo the_title();
                endwhile;
            endif;
            ?>
    </section>
</div>

blog-show.php

<div class="col-12 col-sm-4">
    <a href="<?php echo the_permalink() ?>">
        <img src="<?php the_post_thumbnail(); ?>"
             alt="<?php the_post_thumbnail_caption() ?>"/>
        <h3><?php the_title(); ?></h3>
    </a>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</div>

I am able to use the the_post_thumbnail in another page but it doesn't work here.

Answer 1

the_post_thumbnail displays the post thumbnail. It generates HTML tag and echoes it. It does not echo only the URL to that image.

So this line:

<img src="<?php the_post_thumbnail(); ?>"
         alt="<?php the_post_thumbnail_caption() ?>"/>

Generates something like this:

<img src="<img src="" ... />"
         alt="..."/>

So it's not a correct HTML.

I'd changed it to:

<div class="col-12 col-sm-4">
    <a href="<?php the_permalink(); ?>">
        <?php the_post_thumbnail( 'post-thumbnail', array( 'alt' => get_the_post_thumbnail_caption() ) ); ?>
        <h3><?php the_title(); ?></h3>
    </a>
</div>