PHP - How to check that a string is an int, but not a double, etc.?

Question

PHP has an intval() function that will convert a string to an integer. However I want to check that the string is an integer beforehand, so that I can give a helpful error message to the user if it's wrong. PHP has is_int(), but that returns false for string like "2".

PHP has the is_numeric() function, but that will return true if the number is a double. I want something that will return false for a double, but true for an int.

e.g.:

my_is_int("2") == TRUE
my_is_int("2.1") == FALSE

Answer 1

Could either use is_numeric() then check for presence of "." in the string (not particularly culture-sensitive though).

Alternatively use is_numeric() then cast to a double and see if $var == floor($var) (should return true if it's an integer).

Answer 2

/**
 * Check if a number is a counting number by checking if it
 * is an integer primitive type, or if the string represents
 * an integer as a string
 */
function is_int_val($data) {
    if (is_int($data) === true) return true;
    elseif (is_string($data) === true && is_numeric($data) === true) {
        return (strpos($data, '.') === false);
    } 
    return false;
}

Source.

Answer 3

How about using ctype_digit?

From the manual:

<?php
$strings = array('1820.20', '10002', 'wsl!12');
foreach ($strings as $testcase) {
    if (ctype_digit($testcase)) {
        echo "The string $testcase consists of all digits.\n";
    } else {
        echo "The string $testcase does not consist of all digits.\n";
    }
}
?>

The above example will output:

The string 1820.20 does not consist of all digits.
The string 10002 consists of all digits.
The string wsl!12 does not consist of all digits.

This will only work if your input is always a string:

$numeric_string = '42';
$integer        = 42;

ctype_digit($numeric_string);  // true
ctype_digit($integer);         // false

If your input might be of type int, then combine ctype_digit with is_int.

If you care about negative numbers, then you'll need to check the input for a preceding -, and if so, call ctype_digit on a substr of the input string. Something like this would do it:

function my_is_int($input) {
  if ($input[0] == '-') {
    return ctype_digit(substr($input, 1));
  }
  return ctype_digit($input);
}

Answer 4

+1 to Dominic's answer (using ctype_digit). Another way you could do it is with type coercion:

$inty = "2";
$inty2 = " 2";
$floaty = "2.1";
$floaty2 = "2.0";

is_int($inty + 0); // true
is_int($floaty + 0); // false
is_int($floaty2 + 0); // false

// here's difference between this and the ctype functions.
is_int($inty2 + 0);  // true
ctype_digit($inty2); // false

Answer 5

filter_var should do it:

var_dump(filter_var('2', FILTER_VALIDATE_INT));   // 2
var_dump(filter_var('2.0', FILTER_VALIDATE_INT)); // false
var_dump(filter_var('2.1', FILTER_VALIDATE_INT)); // false

but

var_dump(filter_var(2, FILTER_VALIDATE_INT));     // 2
var_dump(filter_var(2.0, FILTER_VALIDATE_INT));   // 2
var_dump(filter_var(2.1, FILTER_VALIDATE_INT));   // false

If you just want Booleans as return values, wrap it into a function, e.g.

function validatesAsInt($number)
{
    $number = filter_var($number, FILTER_VALIDATE_INT);
    return ($number !== FALSE);
}

Answer 6

Cast it to int. if it still have the same value its int;

function my_is_int($var) {
  $tmp = (int) $var;
  if($tmp == $var)
       return true;
  else
       return false;
}