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up vote 0 down vote favorite

By coincidence I ran into a very bizarre behaviour regarding PHP arrays and its keys. Consider this creation of an PHP array.

$arr[2250572483]=1;
//dump the array
var_dump($arr);
//Result:
array(1) { [-2044394813]=> int(1) }

Somehow the array key has changed its value to a completely different negative number. This led me to some further investigation which is still inconclusive.
In below example I loop between the number range 2250572300 and 2250572500. Time is scarces for me so I did not manage to pinpoint at what number this phenomenon starts occurring because I run out of memory looping through large range of numbers. I think it should be somewhere between 2100000000 and 4300000000.

$arr2 = array();
for($i=2250572300; $i<= 2250572500; $i++){
  $arr2[$i]=$i;
}
echo "<pre>".var_export($arr2,true)."</pre>";

My question is: does anyone know how and why this is happening and is there anything that is currently being done to fix the problem?

Essentially this is a major design flaw within PHP and could potentially make PHP useless when you are working with numbers in arrays, examples being supplier, invoice, item numbers etc.

Thanks

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Seems to work for me: 3v4l.org/6nD3C and the second example too: 3v4l.org/Feooi – WizKid May 22 '14 at 5:09
up vote 1 down vote

You're using an integer value as the array key. All integers in PHP are signed integers and on 32-bit systems, the maximum value is 232 - 1 (given by PHP_INT_MAX). If the integer value is greater than PHP_INT_MAX then it wraps over and gives $key % PHP_INT_MAX as the result.

To confirm:

echo 2250572483 % PHP_INT_MAX; // => -2044394813

The solution would be to use the key as a string, i.e. $arr['2250572483']=1;. This shouldn't be a problem on 64-bit systems, though (where the upper limit is 264 - 1).

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Hi Amal, Simply putting quotes around a number does not make it a string in PHP hence why "3"*4=12 works. $arr['2250572483']=1 still has a problem. Doing things like $arr[(string)2250572483] does not work. I realize the problem is 32bit computer system but I should still be able to explicitly set 2250572483 to be a string value. PHP treats it as a number even it you have it inside quotes. You could do things like $arr["2250572483 "]=1 and then trim it, but why should I have to do workarounds like that. The problem is that PHP interprets a string as a number if all characters are numbers. – tuberider May 22 '14 at 23:57
up vote 0 down vote

That has something to do with how integers are saved. The first bit (from the left side) say if you are positiv + or negativ - and with this behavior the result with big ints will be how you discribted it. That you have a negativ Integer.

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