PHP in_array comparision working differently on different machine

Its very easy .... let me guess your Development system is windows and your production server is linux ?

You are having Integer overflow Issues because most likey your windows version of PHP is 32bit and linux is 64bit

See Condition for array key conversion

• Strings containing valid integers will be cast to the integer type. E.g. the key "8" will actually be stored under 8. On the other hand "08" will not be cast, as it isn't a valid decimal integer.
• 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.
• Bools are cast to integers, too, i.e. the key true will actually be stored under 1 and the key false under 0.
• Null will be cast to the empty string, i.e. the key null will actually be stored under "". Arrays and objects can not be used as keys. Doing so will result in a warning: Illegal offset type.

So what happens is that :

So the key 28000000000000003 is a valid integer on a 64bit but a String on a 32bits system

I was able to replicate your issue

echo "<pre>";
$data = array("28000000000000003" => 'ABC',"28000000000000001" => 'PQR');
$keys = array("28000000000000003","28000000000000001");
$keysDerived = array_keys($data);

var_dump(in_array("28000000000000003", $keysDerived, true));
var_dump(in_array("28000000000000003", $keysDerived));
var_dump(in_array("28000000000000003", $keys, true));
var_dump(in_array("28000000000000003", $keys));

Output

bool(false)    <----------------------- false instead of true 
bool(true)
bool(true)
bool(true)

This issues has nothing to do with in_array but rather array_keys example

Sample Code

echo "<pre>"; 
$data = array("28000000000000003" => 'ABC',"28000000000000001" => 'PQR');
$keys = array("28000000000000003","28000000000000001");
$keysDerived = array_keys($data);
var_dump($keys,$keysDerived);

Output

array(2) {
  [0]=>
  string(17) "28000000000000003"    <------- Keys are String
  [1]=>
  string(17) "28000000000000001"
}
array(2) {
  [0]=>
  int(28000000000000003)           <------- They are converted to int on 64bits
  [1]=>
  int(28000000000000001)
}

See Online Demo

This means that they are not the same type ...

in_array bool in_array ( mixed $needle , array $haystack [, bool $strict = FALSE ] )

If the third parameter strict is set to TRUE then the in_array() function will also check the types of the needle in the haystack.

If you run this code

foreach ( $keys as $key ) {
    echo gettype($key) . "\n";
}

foreach ( $keysDerived as $key ) {
    echo gettype($key) . "\n";
}

Output 64Bits

string
string
integer
integer

Output 32Bits

string
string
string
string

Simple Workaround

echo "<pre>";
$data = array("28000000000000003" => 'ABC',"28000000000000001" => 'PQR');
$keys = array("28000000000000003","28000000000000001");
$keysDerived = array_keys_string($data);
var_dump($keys,$keysDerived);

var_dump(in_array("28000000000000003", $keysDerived, true));
var_dump(in_array("28000000000000003", $keysDerived));
var_dump(in_array("28000000000000003", $keys, true));
var_dump(in_array("28000000000000003", $keys));

Output

array(2) {
  [0]=>
  string(17) "28000000000000003"
  [1]=>
  string(17) "28000000000000001"
}
array(2) {
  [0]=>
  string(17) "28000000000000003"
  [1]=>
  string(17) "28000000000000001"
}
bool(true)
bool(true)
bool(true)
bool(true)

See Original Code See Modified Code

Function Used

function array_keys_string(array $input) {
    $list = array();
    foreach ( $input as $k => $v ) {
        $list[] = (string)$k;
    }
    return $list;
}