Warning: Massive error in json_encode()

Question

<?php  
$int = 1968401665333658496;  
echo json_encode( array("$int",$int) );  
?>  

Recieved in browser: [ "1968401665333658496" , 1968401665333658600 ]

It "rounds off" my integer?

Btw : PHP_INT_MAX = 9223372036854775807 ~ PHP Version 5.3.2-1ubuntu4.7
No problems with these huge integers anywhere (PHP, MySQL or Javascript)
- until json_encode() screws it up (silently btw..)

Answer 1

It's not just a JSON issue. If you put

alert(1968401665333658496);

in firebug console you get 1968401665333658600

You're probably hitting the JS max value.

There's a discussion on that here : What is JavaScript's highest integer value that a Number can go to without losing precision?

Answer 2

Javascript has no concept of integers, according to the standard all numbers are IEEE doubles, which means they have 52 bits of mantissa. this leads to a practical maximum "integer" value of 2^53 before any loss of precision.

I am not sure how you didn't have problems with numbers this large in JS alone - if you didn't your JS implementation is not standards compliant.