php - Wordpress Core Data Validation Functions not working -

i'm developing custom theme wordpress site , want use wordpress core data validation functions validate info forms.

every time try use sanitize_text_field() function error:

fatal error: call undefined function sanitize_text_field().

i've read many posts similar issues, specially using $wpdb, none of them seem work.

the file in i'm trying use sanitation functions inside theme directory, in case piece of info helps solve mystery.

i've seen posts talking including wp-load.php , formatting.php files none of attempts has worked yet.

ok, kept searching , found solution, adding next line of code beginning of file solved problem:

require_once( explode( "wp-content" , __file__ )[0] . "wp-load.php" ); 

i hope helps else too.