How to Get Category Names by Post ID in WordPress!

$postId = 1;
//note: if you code in single.php, do not need to pass the id
$categories = get_the_category($postId);

//iterate categories and print $category->cat_name
foreach($categories as $category){
    echo '<a href="' . get_category_link($category) . '">' . $category->cat_name . '</a>';
}

Explaining the above code

In the first line, we specified $postId as the post with an ID of 1. But you do not need to specify the post id if you are coding inside the single.php file.

the get_the_category() function will use the global $post object to return categories if you do not pass the post id.

Then in line 3, we retrieved categories using the get_the_category() function.

get_the_category() will return an array of category objects containing the cat_name field, which we are looking for.

We used foreach loop from line 6 to iterate categories and print the $category->cat_name wrapped inside <a> tag.

If you do not need to link the category name to its page, then remove the link tag, like the below example:

$postId = 1;
//note: if you code in single.php, do not need to pass the id
$categories = get_the_category($postId);

//iterate categories and print $category->cat_name
foreach($categories as $category){
    echo $category->cat_name . ',';
}

If you need category names inside an array to use inside custom functions or WordPress plugin development, try the below code:

$postId = get_the_ID();

//retrieve categories for this post
$categories = get_the_category($postId);

//create an array of category names
$categoryNames = array_map( function($category){ return $category->cat_name; }, $categories );

In the above example, we’ve used the PHP array_map function to create an array of category names.

If you are interested in more details about categories in WordPress, I recommend reading my tutorial on Query WordPress Categories.