Featured Images & Post Thumbnails

https://developer.wordpress.org/themes/functionality/featured-images-post-thumbnails/

Function Reference
add_image_size() – Register a new image size.
set_post_thumbnail_size() – Registers an image size for the post thumbnail.

has_post_thumbnail() – Check if post has an image attached.
the_post_thumbnail() – Display Post Thumbnail.

get_the_post_thumbnail() – Retrieve Post Thumbnail.
get_post_thumbnail_id() – Retrieve Post Thumbnail ID.

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<?php
// 获取所有可用的图片尺寸
$available_sizes = get_intermediate_image_sizes();

// 检查默认尺寸是否存在
$thumbnail_exists = in_array('thumbnail', $available_sizes);
$medium_exists = in_array('medium', $available_sizes);
$large_exists = in_array('large', $available_sizes);

// 输出检测结果
echo "<p>缩略图 (thumbnail): " . ($thumbnail_exists ? "✅ 存在" : "❌ 不存在") . "</p>";
echo "<p>中等尺寸 (medium): " . ($medium_exists ? "✅ 存在" : "❌ 不存在") . "</p>";
echo "<p>大尺寸 (large): " . ($large_exists ? "✅ 存在" : "❌ 不存在") . "</p>";

// 扩展功能：获取所有尺寸详细信息
global $_wp_additional_image_sizes;
$all_sizes = array_merge(
    array(
        'thumbnail' => array(
            'width'  => get_option('thumbnail_size_w'),
            'height' => get_option('thumbnail_size_h'),
            'crop'   => get_option('thumbnail_crop')
        ),
        'medium' => array(
            'width'  => get_option('medium_size_w'),
            'height' => get_option('medium_size_h'),
            'crop'   => false
        ),
        'large' => array(
            'width'  => get_option('large_size_w'),
            'height' => get_option('large_size_h'),
            'crop'   => false
        )
    ),
    $_wp_additional_image_sizes
);

// 显示所有尺寸及其参数
echo "<h3>所有可用图片尺寸：</h3>";
foreach ($all_sizes as $name => $size) {
    echo "<p><strong>{$name}</strong>: {$size['width']}×{$size['height']} " 
         . ($size['crop'] ? "(裁剪)" : "(缩放)") . "</p>";
}
?>