Analysis of related PHP functions for debugging thumbnails in WordPress_php tips

the_post_thumbnail
the_post_thumbnail is mainly used in WordPress to print the thumbnail set in the article, and the get_the_post_thumbnail function can return the HTML code you need in the form of a string.

Usage of the_post_thumbnail function

the_post_thumbnail( $size , $attr)

Function parameters

• $size refers to the type of thumbnail you want. The default is ‘post-thumbnail’, which is the featured image
• $attr attribute settings in the image img tag.

the_post_thumbnail function declaration

/**
 * Display Post Thumbnail.
 *
 * @since 2.9.0
 *
 * @param int $size Optional. Image size. Defaults to 'post-thumbnail', which theme sets using set_post_thumbnail_size( $width, $height, $crop_flag );.
 * @param string|array $attr Optional. Query string or array of attributes.
 */
function the_post_thumbnail( $size = 'post-thumbnail', $attr = '' ) {
 echo get_the_post_thumbnail( null, $size, $attr );
}
get_the_post_thumbnail 函数声明
 * Retrieve Post Thumbnail.
 *
 * @since 2.9.0
 *
 * @param int $post_id Optional. Post ID.
 * @param string $size Optional. Image size. Defaults to 'post-thumbnail'.
 * @param string|array $attr Optional. Query string or array of attributes.
 */
function get_the_post_thumbnail( $post_id = null, $size = 'post-thumbnail', $attr = '' ) {
 $post_id = ( null === $post_id ) ? get_the_ID() : $post_id;
 $post_thumbnail_id = get_post_thumbnail_id( $post_id );
 $size = apply_filters( 'post_thumbnail_size', $size );
 if ( $post_thumbnail_id ) {
 do_action( 'begin_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size ); // for "Just In Time" filtering of all of wp_get_attachment_image()'s filters
 if ( in_the_loop() )
  update_post_thumbnail_cache();
 $html = wp_get_attachment_image( $post_thumbnail_id, $size, false, $attr );
 do_action( 'end_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size );
 } else {
 $html = '';
 }
 return apply_filters( 'post_thumbnail_html', $html, $post_id, $post_thumbnail_id, $size, $attr );

set_post_thumbnail_size
The set_post_thumbnail_size function is a function in WordPress that sets the size of featured images and is a simple application of the add_image_size function. In order to better highlight the use of featured images, WordPress has had this function since version 2.9.0.

Usage of set_post_thumbnail_size function
It is roughly similar to the add_image_size function, except that this function is only set for the featured image.

set_post_thumbnail_size( $width, $height, $crop)

Detailed explanation of parameters

• $width image width
• $height image height
• $crop Whether to crop the image according to height and width

Example

set_post_thumbnail_size(100,0,true);

Note: When either height or width is 0, WP will automatically adapt to the other value for thumbnail generation.

Function declaration

/**
 * Registers an image size for the post thumbnail
 *
 * @since 2.9.0
 */
function set_post_thumbnail_size( $width = 0, $height = 0, $crop = false ) {
 add_image_size( 'post-thumbnail', $width, $height, $crop );