Definition and Usage

PHP Version
4+

The is_bool() function checks whether a given value is a boolean.
It returns true if the value passed as an argument is a boolean; otherwise, it returns false.

The boolean type represents a data type that can only have one of two values: true (true) or false (false).
In PHP, although integers and strings can be evaluated as booleans in conditional expressions, the boolean type itself only has the two values, true and false.

Basic Example

PHP 
/* Boolean type */
var_dump(is_bool(true));    // bool(true)
var_dump(is_bool(false));   // bool(true)

/* Numbers */
var_dump(is_bool(1));       // bool(false)
var_dump(is_bool(0));       // bool(false)

/* Strings */
var_dump(is_bool('hello')); // bool(false)
var_dump(is_bool('true'));  // bool(false)
var_dump(is_bool('false')); // bool(false)

/* The result of comparison operators (e.g., ===, !==) is always a boolean value */
var_dump(is_bool(1 === 1)); // bool(true)
var_dump(is_bool(1 !== 1)); // bool(true)

Note:
The gettype() function returns the data type of the given value as a string.

Syntax

PHP 
is_bool(mixed $value): bool

Parameters

Description of the is_bool() function parameters
$value Required. The value to check.

Return Values

If the value passed as an argument is a boolean, the function returns true; otherwise, it returns false.

Things to Keep in Mind

The is_bool() function returns true only when the value exactly matches the boolean type. Therefore, in the following examples, each call returns false:

PHP 
$a = null;
$b = '';
$c = 0;

var_dump(is_bool($a)); // bool(false)
var_dump(is_bool($b)); // bool(false)
var_dump(is_bool($c)); // bool(false)

Practical Examples

The is_bool() function is convenient and useful in the following situations:

When Checking if a Variable is of Boolean Type

When you need to check if a variable is of boolean type, you can use the is_bool() function to write more concise code. For example, the following code checks if a variable is of boolean type and performs different actions accordingly:

PHP 
$a = true;

if (is_bool($a)) {
    echo 'Variable $a is of boolean type.';
} else {
    echo 'Variable $a is not of boolean type.';
}

// Output: 'Variable $a is of boolean type.'

When Using in Conditional Statements

When you need to check if a variable is of boolean type in a conditional statement, the is_bool() function allows you to write clear code. For example, the following code only performs a specific action if the variable is true:

PHP 
$a = true;

if (is_bool($a) && $a === true) {
    echo 'Variable $a is TRUE.';
} else {
    echo 'Variable $a is not TRUE.';
}

// Output: 'Variable $a is TRUE.'

When Using as a Function Argument

If a function argument should be of boolean type, you can use the is_bool() function to ensure the variable is of the correct type. For example, the following code uses is_bool() to check the type before passing the variable as an argument to a function:

PHP 
function my_function($bool) {
    if ($bool === true) {
        echo 'The variable is TRUE.';
    } else {
        echo 'The variable is not TRUE.';
    }
}

$a = 1;

my_function(is_bool($a)); // Output: 'The variable is not TRUE.'

References

See also