PHP is_finite(), is_infinite(), is_nan() Functions

Given any numerical value, it can be classified into 3 different classes such as Finite Number, Infinite Number, and Not a Number or commonly known as NaN. While developing a project that is highly dependent on User Inputs there might be many cases where the user provides inappropriate inputs while a function expects a finite numerical input thus creating an unhandled situation or unexpected result.

Thus it is a secure option to check whether a given input value is finite or not.

is_finite() Function

Syntax:

bool is_finite ($value)

Parameters: The function takes a single parameter which is a float that is to be checked.

Return Type: This function returns TRUE if the given value is finite otherwise returns FALSE.

Examples:

Input :  $value = M_PI_4;
Output : TRUE

Input : $value = log(0);
Output : FALSE        

is_infinite() Function

Syntax:

bool is_infinite ($value)

Parameters: The function takes a single parameter which is a float that is to be checked.

Return Type: This function returns TRUE if the given value is infinite otherwise returns FALSE.

Examples:

Input :  $value = M_PI_4;
Output : FALSE

Input : $value = log(0);
Output : TRUE        

is_nan() Function

Syntax:

bool is_nan ($value)

Parameters: The function takes a single parameter which is a float that is to be checked.

Return Type: This function returns TRUE if the given value is not a number otherwise returns FALSE.

Examples:

Input :  $value = M_PI_4;
Output : FALSE

// cos function can not be greater than 1
Input : $value = acos(1.1); 
Output : TRUE        

Below program illustrates the working of is_finite(), is_infinite(), is_nan() functions in PHP:

<?php

// PHP code to illustrate the working of
// is_finite(), is_infinte() and is_nan()
// Functions

// Finite Value: PI
$val1 = M_PI;

// In-built value of INFINITY
$val2 = INF;

// Produces NaN as COS value can reside
// between -1 to +1 both inclusive
$val3 = acos(-1.01);

echo var_dump(is_finite($val1),
    is_finite($val2), is_finite($val3)) . "\n";

echo var_dump(is_infinite($val1),
    is_infinite($val2), is_infinite($val3)) . "\n";

echo var_dump(is_nan($val1),
    is_nan($val2), is_nan($val3)) . "\n";

?>

Output:

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

Note:

• This function can also check whether an expression produces finite result, but in case of expressions that lead to NaN. PHP itself shows error and default FALSE is returned, such as in case of checking a Divided by Zero expression.
• The is_finite() Function is used in many projects to make it more secure and efficient.
• These methods produce highly accurate results but is not much time efficient.