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php – Why does is_numeric(NAN) return TRUE?

Posted by: admin July 12, 2020 Leave a comment


I have tested the is_numeric function in the NAN constant in PHP and the given result

is_numeric(NAN); // TRUE

But NAN means “Not A Number”. Why the function is_numeric returns true?

I know that NAN is of float type. But when testing the two cases below, the results are different:

is_float(NAN) // true
filter_var(NAN, FILTER_VALIDATE_FLOAT)// false

Why ocurred it?

Sorry, my english is bad

How to&Answers:

NAN is a special constant. It has to hold some value, so it holds a float datatype

var_dump(NAN); // float(NAN);

The problem is that filter_var isn’t comparing data types, it’s looking for numbers, which NAN is not.

Some numeric operations can result in a value represented by the constant NAN. This result represents an undefined or unrepresentable value in floating-point calculations. Any loose or strict comparisons of this value against any other value, including itself, will have a result of FALSE.

Because NAN represents any number of different values, NAN should not be compared to other values, including itself, and instead should be checked for using is_nan().


NAN is a non-zero floating point value. What is NAN, Its a square root of (-1).

So now it comes to complex numbers. Square root of (-1) is +i or -i which means NAN can have two values. So if NAN were to evaluate to -i or false, NAN == false would become true instead.