There are many predefined Filter Constants in PHP which is passed as a second parameter value in the filter_var() function. Some of them are:

• FILTER_VALIDATE_BOOLEAN: Used to validate a boolean.
• FILTER_VALIDATE_EMAIL: It is used to validate an email address.
• FILTER_VALIDATE_FLOAT: It is used to validate a float.
• FILTER_VALIDATE_INT: It is used to validate an integer.
• FILTER_VALIDATE_IP: It is used to validate an IP address.
• FILTER_VALIDATE_URL:It is used to validate an URL address.
• FILTER_SANITIZE_ENCODED: It removes/encodes special characters.
• FILTER_SANITIZE_NUMBER_FLOAT: It removes characters such as:except digits, +- and etc.
• FILTER_SANITIZE_SPECIAL_CHARS: It removes special characters
• FILTER_SANITIZE_URL: It removes all illegal character from s URL
• FILTER_SANITIZE_NUMBER_INT: It removes all characters except digits and + -
• FILTER_CALLBACK: It is used to call a user defined function to filter the data.