Check to see if string is an integer (includes negative numbers) PHP

Question

The function below checks if a string is an integer meaning it should only contain digits. But it does not check if number is negative (negative numbers should return true as well since they are integers).

function validateInteger($value)
{
   //need is_numeric to avoid $value = true returns true with preg_match
   return is_numeric($value) && preg_match('/^\d+$/', $value);
}

I ran tests and got results:

'12.5'      => FALSE 
12.5        => FALSE 
'a125'      => FALSE 
'125a'      => FALSE 
'1a2.5'     => FALSE 
125         => TRUE 
'abc'       => FALSE 
false       => FALSE 
true        => FALSE 
'false'     => FALSE 
'true'      => FALSE 
null        => FALSE 
'null'      => FALSE 
'1231'      => TRUE 
-1231       => FALSE (SHOULD RETURN TRUE)
'-1231'     => FALSE (SHOULD RETURN TRUE)

I dont want to use itnval() < 0. I would prefer regular expression to check for negative numbers as well.

Thanks

EDIT:

I also have a function validateFloat that returns true if a given number is floating number meaning it can contain only digits and a dot. I need to apply same logic to this as well so that it returns true for negative floating numbers

Community · Accepted Answer · 2023-11-17 20:33:26Z

4

is_int isn't good enough for you?

filter_var($input, FILTER_VALIDATE_INT) should have the same effect but also work on strings.

edited Nov 17, 2023 at 20:33

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answered Apr 17, 2013 at 18:07

Explosion Pills

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5 Comments

GGio Over a year ago

but that returns false if value is a string but contains all digits. In my case '125' and '-1231' would return false

GGio Over a year ago

filter_var($input, FILTER_VALIDATE_INT) returns true if the $input = true. it should be false in that case

Explosion Pills Over a year ago

@GGio Try adding the option FILTER_NULL_ON_FAILURE

Explosion Pills Over a year ago

@GGio actually it seems like it will get cast to an int, so I think you just need to do an explicit check $input !== true && filter_var(...

codekandis Over a year ago

filter_var( '-010', FILTER_VALIDATE_INT ) leads to a false negative, while (int)'-010' returns -10.

raidenace · Accepted Answer · 2013-04-17 18:12:46Z

1

just use is_numeric(abs($val))

answered Apr 17, 2013 at 18:12

raidenace

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2 Comments

raidenace Over a year ago

@GGio well then is_numeric($val) && is_numeric(abs($val))

codekandis Over a year ago

My DownVote: is_numeric( abs( '125a' ) ) leads to a false positive.

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