将此函数添加到函数中。php文件：

function show($size = NULL) {
    global $post;
    $post_thumbnail_id = get_post_thumbnail_id( $post->ID );
    if(isset($size)){
        $image_data_array = wp_get_attachment_image_src($post_thumbnail_id,$size);
    }else{
        $image_data_array = wp_get_attachment_image_src($post_thumbnail_id);//Default value: \'thumbnail\'
    }
    echo $image_data_array[1]."x".$image_data_array[2];//here you can add more chars of strings if you want
}

<a class="classname" href="<?php the_post_thumbnail_url( \'full\' ); ?>">Full Image <?php show(\'full\'); ?></a>