FILTER_VALIDATE_BOOLEAN constant in PHP

The FILTER_VALIDATE_BOOLEAN constant validates a value as a boolean option. It's useful when you need to convert string representations of boolean values into actual PHP boolean types.

Return Value

The FILTER_VALIDATE_BOOLEAN constant returns:

• TRUE for "1", "true", "on" and "yes"
• FALSE for "0", "false", "off" and "no"
• NULL for any other value

Syntax

filter_var($value, FILTER_VALIDATE_BOOLEAN, $flags)

Example 1: Valid TRUE Values

This example shows values that return TRUE −

<?php
    $var = "on";
    var_dump(filter_var($var, FILTER_VALIDATE_BOOLEAN));
    
    $var2 = "true";
    var_dump(filter_var($var2, FILTER_VALIDATE_BOOLEAN));
    
    $var3 = "1";
    var_dump(filter_var($var3, FILTER_VALIDATE_BOOLEAN));
?>

bool(true)
bool(true)
bool(true)

Example 2: Valid FALSE Values

This example demonstrates values that return FALSE −

<?php
    $var = "off";
    var_dump(filter_var($var, FILTER_VALIDATE_BOOLEAN));
    
    $var2 = "false";
    var_dump(filter_var($var2, FILTER_VALIDATE_BOOLEAN));
    
    $var3 = "0";
    var_dump(filter_var($var3, FILTER_VALIDATE_BOOLEAN));
?>

bool(false)
bool(false)
bool(false)

Example 3: Invalid Values

Invalid values return NULL −

<?php
    $var = "invalid";
    var_dump(filter_var($var, FILTER_VALIDATE_BOOLEAN));
    
    $var2 = "maybe";
    var_dump(filter_var($var2, FILTER_VALIDATE_BOOLEAN));
?>

NULL
NULL

Conclusion

FILTER_VALIDATE_BOOLEAN is perfect for validating user input that represents boolean values. It safely converts string representations to proper PHP boolean types or returns NULL for invalid input.