PHP function for input sanitizing

In PHP, there are several functions for input sanitizing:

1) strip_tags — Strip HTML and PHP tags from a string

 2)

htmlspecialchars — Convert special characters to HTML entities

3) 

htmlentities — Convert all applicable characters to HTML entities

 htmlentities converts more characters  to HTML entities than htmlspecialchar, and has more options.

4)

  mysqli_real_escape_string is used for MySQL  database sanitizing. It removes special characters that could be considered dangerous when passed into a database.  

 another function

addslashes — Quote string with slashes

 addslashes  is less powerful than mysqli_real_escape_string

5)

filter_var — Filters a variable with a specified filter