Getting Permalink within the loop

Question

I have a (Roots/Sage-based) theme with a home.php template override and on that page am displaying excerpts and featured image for each post.

<?php while (have_posts()) : the_post(); ?>  
  <div class=".container-fluid">
    <?php if (get_post_type() == 'instruments') {?>
    <div class="col-md-3">
        <h1><?php the_ID(); ?></h1>
        <a href="<?php get_post_permalink(the_permalink()) ?>"><?php the_post_thumbnail( 'medium' ); ?></a>
        <?php get_template_part('templates/content', get_post_type() != 'post' ? get_post_type() : get_post_format()); ?>
    </div>
  </div>
<?php } ?>

<?php endwhile; ?>

Seems relatively simple and is working, but it was just by trial and error that I came up with generating the link via:

 get_post_permalink(the_permalink())

And since there are so many wrong ways to do php (and wp), I'd love some feedback.

Answer 1

As suggested, went to the function reference and from there to the Source File (located in wp_includes/link-template.php) in which there are four functions that each return similar results.

    <?php echo get_post_permalink() ?>

http://newdep.localhost/instruments/jester/

    <?php echo post_permalink() ?>

http://newdep.localhost/instruments/jester/

    <?php the_permalink() ?>

/instruments/jester/

    <?php echo get_the_permalink() ?>

http://newdep.localhost/instruments/jester/

In this case, since this is a custom post type, the function which the docs describe as being designed for it, is get_post_permalink(), which, as most of of the get_*() functions returns, rather than showing a result, needs to be echo'd.

/**
 * Retrieve the permalink for a post with a custom post type.
 *
 * @since 3.0.0
 *
 * @param int $id Optional. Post ID.
 * @param bool $leavename Optional, defaults to false. Whether to keep post name.
 * @param bool $sample Optional, defaults to false. Is it a sample permalink.
 * @return string The post permalink.
 */
function get_post_permalink( $id = 0, $leavename = false, $sample = false ) {
    global $wp_rewrite;

    $post = get_post($id);

    if ( is_wp_error( $post ) )
        return $post;

    $post_link = $wp_rewrite->get_extra_permastruct($post->post_type);

    $slug = $post->post_name;

    $draft_or_pending = isset( $post->post_status ) && in_array( $post->post_status, array( 'draft', 'pending', 'auto-draft', 'future' ) );

    $post_type = get_post_type_object($post->post_type);

    if ( $post_type->hierarchical ) {
        $slug = get_page_uri( $id );
    }

    if ( !empty($post_link) && ( !$draft_or_pending || $sample ) ) {
        if ( ! $leavename ) {
            $post_link = str_replace("%$post->post_type%", $slug, $post_link);
        }
        $post_link = home_url( user_trailingslashit($post_link) );
    } else {
        if ( $post_type->query_var && ( isset($post->post_status) && !$draft_or_pending ) )
            $post_link = add_query_arg($post_type->query_var, $slug, '');
        else
            $post_link = add_query_arg(array('post_type' => $post->post_type, 'p' => $post->ID), '');
        $post_link = home_url($post_link);
    }

    /**
     * Filter the permalink for a post with a custom post type.
     *
     * @since 3.0.0
     *
     * @param string  $post_link The post's permalink.
     * @param WP_Post $post      The post in question.
     * @param bool    $leavename Whether to keep the post name.
     * @param bool    $sample    Is it a sample permalink.
     */
    return apply_filters( 'post_type_link', $post_link, $post, $leavename, $sample );
}

Answer 2

As Nilambar mentioned, the correct function is <?php the_permalink(); ?>.

However, if you are using trial and error - try the WordPress Codex, particularly the_permalink for more info, examples and related functions.