如何将自定义字段链接应用于幻灯片按钮？

I created a relational custom field (slide_link) to link my slides to pages, but i am having difficulty applying the link to my slider button in the home.php file. Here are my codes:

<div class="flexslider">
          <ul class="slides">
            <?php
                 $query = new WP_Query( array('post_type' => 'slide') );
                 while ( $query->have_posts() ) : $query->the_post();
             ?>

            <?php
                $thumb = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'thumbnail_size' );
                $url = $thumb['0'];
            ?>

            <?php
                  global $post;
                  $meta = get_post_meta( $post->ID );
                  $captn      = isset( $meta['caption'][0] )  ? filter_var( $meta['caption'][0],  FILTER_SANITIZE_STRING ) : '';
                  $slideurl   = isset( $meta['slide_link'][0] )  ? filter_var( $meta['slide_link'][0],  FILTER_SANITIZE_STRING ) : '';
            ?>

             <li data-thumb="<?php echo $url; ?>">
                <img src="<?php echo $url; ?>" />
                <p class="flex-caption"> <?php echo($captn); ?> </p>
                <a href="<?php echo $slideurl; ?>" class="flex-link">See More</a>
            </li>

            <?php endwhile; ?>
        </ul>
    </div><!-- /home banner -->

Function.php where I registered the custom field

//function to register vision field
    add_filter('the_permalink', 'getCustomFeature6');
    function getCustomFeature6($slideurl) {
        global $post;
        $meta = get_post_meta($post->ID, 'slider_link', true);
        return $slideurl;
    }

Any help would be appreciated!

I do not understand why are you using add_filter('the_permalink', 'getCustomFeature6'); . I would use this:

<?php $slideurl = get_post_meta($post->ID, "slider_link", true); ?>
<li data-thumb="<?php echo $url; ?>">
    <img src="<?php echo $url; ?>" />
    <p class="flex-caption"> <?php echo($captn); ?> </p>
    <a href="<?php echo $slideurl; ?>" class="flex-link">See More</a>
</li>