What is WordPress has_post_thumbnail function?

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has_post_thumbnail() is a function that identifies the presence of image in a post. This function signifies the featured image that has been attached to the post.

has_post_thumbnail() Function:

This function enables easy identification of featured image attached to a post by getting the direct image URL for the featured image.

<? php

has_post_thumbnail( $post_id );

?>

Parameters:

$post_id: This optional parameter can be used to define the ID of the post that needs to identify the featured image’s presence. The default parameter is global $post. The default value gives null. The function returns bool i.e. whether the post has image attached or not.

Examples:

  1. Default Size: To check whether a Post has a thumbnail assigned to it with default value null.

<? php

if ( has_post_thumbnail() {

the_post_thumbnail_url();

}

?>

 

  1. Varied thumbnail sizes: WordPress has default image sizes of thumbnail, medium, large, and full. Following functions show how these default sizes can be used with the_post_thumbnail() function:
  • Post thumbnail without parameter
    • the_post_thumbnail_url();
  • Post thumbnail (150px x 150px max)
    • the_post_thumbnail_url( ‘thumbnail’ );
  • Post thumbnail Medium (300px x 300px max)
    • the_post_thumbnail_url( ‘medium’ );
  • Post thumbnail Large ( 640px x 640px max)
    • the_post_thumbnail_url( ‘large’ );
  • Post thumbnail Full (original size uploaded)
    • the_post_thumbnail_url( ‘full’ );

Uses:

The function’s source is wp-includes/post-thumbnail-template.php and the basic code snippet is

function has_post_thumbnail( $post = null ) {

return (bool) get_post_thumbnail_id( $post );

}

The function is further used by wp-includes/post-template.php and wp-includes/embed.php

Tips to use has_post_thumbnail:

To configure the featured post in theme, in functions.php file add the following snippet

if ( has_post_thumbnail() ) {

the_post_thumbnail();

}

else {

echo ‘<img src=”‘ . get_bloginfo( ‘stylesheet_directory’ )

. ‘/images/thumbnail-default.jpg” />’;

}

 

Also,

add_theme_support( ‘post-thumbnails’ );

set_post_thumbnail_size(200,200); // W x H, hard crop

It will place the image on the post page in admin section and also adjust its size according to the requirement. It improves the usability of the theme.

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