why i am getting wrong array count in php

Question

$array = array (0.1 => 'a', 0.2 => 'b');
echo count ($array);

It overwrites first array element by second, just because, I used float with 0.

And hence output of above code is 1, instead of 2.

Why PHP round array index down to 0 ?

Answer 1

The array keys are interpreted as numeric, but numeric keys must be integers, Therefore, both float values are cast (truncated) to integer zero and 0.2 overwrites 0.1.

var_dump($array);
array(1) {
  [0]=>
  string(1) "b"
}

Make the array keys strings if you want to use non integer values:

$array = array ("0.1" => 'a', "0.2" => 'b');
echo count($array);
// 2

array(2) {
  ["0.1"]=>
  string(1) "a"
  ["0.2"]=>
  string(1) "b"
}

Answer 2

Only integer is allowed as key of the array.

See what we get if I print_r($array):

Array ( [0] => b )

However you can do like this:

$array = array ('0.1' => 'a', '0.2' => 'b');

Now print_r says this:

Array ( [0.1] => a [0.2] => b )

Answer 3

Array indices cannot be floats. They must be either integers or strings. If you would try to var_dump($array); you would see that your array looks something like this:

array(1) { 
    [0]=> string(1) "b" 
}

You are effectively trying to set value for key 0 twice.

Answer 4

You cannot use floats as numeric keys. 0.1 and 0.2 both get converted to 0

Either you have to use integers or strings. Therefore, your options are:

$array = array ('0.1' => 'a', '0.2' => 'b');

Or:

$array = array (1 => 'a', 2 => 'b');

Answer 5

Let's see what the PHP's own excellent manual says about arrays (emphasis mine):

The key can either be an integer or a string. The value can be of any type.

Additionally the following key casts will occur: [...] Floats are also cast to integers, which means that the fractional part will be truncated.

So, if you look at your array:

<?php
$array = array (0.1 => 'a', 0.2 => 'b');
var_dump($array); // let's see what actually *is* in the array
echo count ($array);

you'll get this back:

array(1) {
  [0]=>
  string(1) "b"
}
1

So, first your array is { 0 => 'a' }, then becomes { 0 => 'b' }. The computer did exactly what you asked it to, even if not what you intended.

Possible solution: pass the array keys as strings - there is no conversion to int, and it works as expected.

$array = array ('0.1' => 'a', '0.2' => 'b');

Answer 6

You must use quote on non-integer keys

$array = array ('0.1' => 'a', '0.2' => 'b');
echo count($array);

Answer 7

You are storing 'a' into the 0.1th element and 'b' into the 0.2nd element. This is impossible. Array indexes must be integers.

Perhaps you are wanting to use associative arrays?

$array = array ('0.1' => 'a', '0.2' => 'b');

Answer 8

As per the php.net document on arrays for having keys:

Additionally the following key casts will occur: Floats are also cast to integers, which means that the fractional part will be truncated. E.g. the key 8.7 will actually be stored under 8.

i tried dumping and interpreting the result... 0.1 and 0.2 will be interpreted as 0 and the latter overwrites the former, end result is that the array key remains 0 and value is set as b.

Hence there's nothing wrong with this behavior.

Answer 9

its because floats are casted to integers, so the second entry overwrites the first.

Actually you are doing this:

$array = array (0 => 'a', 0 => 'b');
echo count ($array);

Php.net Array: "Floats are also cast to integers, which means that the fractional part will be truncated. E.g. the key 8.7 will actually be stored under 8."