Question

My understanding is…

if is_numeric($input) === true

then either

is_float($input) === true OR

is_int($input) === true OR

$input === 0 OR

$input is a numeric string (meaning it’d satisfy one of the first 3 if it weren’t wrapped in quotes).

Is that accurate? Are there other differences?

Answer 1

See PHP’s documentation on is_numeric. It talks about everything that is allowed, and it’s more than is_float and is_int.

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It’s also important to note that is_int only works on things that are type integer, meaning string representations are not allowed. This is a common problem when verifying that form input is an integer. You should use filter_var or something from the filter family with the filter FILTER_VALIDATE_INT. For floats, use FILTER_VALIDATE_FLOAT.

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Also, if the reason you are trying to check for an integer is to validate a parameter as being an int, then in PHP 7 you can do this:

function foo(int $i) {
    // $i is guaranteed to be an int (is_int) will be true
}

PHP 7 has two different modes for converting to int; this answer explains it a bit more.

Note that this is probably not what you want if you are validating the contents of a form element. Use the filter_var solution for that.