is_null() function detects whether a variable is NULL null is a special data type in PHP that represents a null value, which means that no value null (null value) is set for the variable For example: < ;?php$str = '';var_dump(is_null($str));//returns false. Although the variable $str is assigned a value of empty, it is not of null type, so it returns false var_dump($str == null);//Return true, == only determines whether the values are equal, not the type of data, so the empty value of the variable $str is equal to null (equivalent to empty value)var_dump($str === null);//Return false, === not only determines whether the values are equal, but also determines the type of data, so the empty value of the variable $str (character string) is not equal to null (special data type)?>
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