PHP json sometimes converts float numbers to integer

Question

Given a float number, after a json encoding and a subsequent decoding, the variable type float (or double) sometimes it's not preserved.

$n1 = 1.23;
$json = json_encode($n1); // '1.23'
$n2 = json_decode($json);

$t1 = gettype($n1); // 'double'
$t2 = gettype($n2); // 'double'

$d = $n1 === $n2; // true

However, when decimals are '0' the result is different:

$n1 = 1.0;
$json = json_encode($n1); // '1'
$n2 = json_decode($json);

$t1 = gettype($n1); // 'double'
$t2 = gettype($n2); // 'integer'

$d = $n1 === $n2; // false

I have to conclude that the behaviour of the json encode / decode functions is based on data value, therefore hard to predict, and ultimately quite inconsistent.

Is there any way to ensure to preserve the type of the variable during the json encode / decode process?

Answer 1

The JSON format on its own, has no notion of floats and integers, it just has numbers. This is one of the reasons why it is a language-independent data format.

However, I've found that the json_encode option JSON_PRESERVE_ZERO_FRACTION does the trick.

JSON_PRESERVE_ZERO_FRACTION

Ensures that float values are always encoded as a float value. Available since PHP 5.6.6.

It forces json_encode to always put at least a '0' decimal digit to the JSON notation.

json_decode, for its part, is natively able to interpret numbers with decimal digits into float, and it doesn't need any special flag.

$n1 = 1.0;
$json = json_encode($n1, JSON_PRESERVE_ZERO_FRACTION); // '1.0'
$n2 = json_decode($json);

$t1 = gettype($n1); // 'double'
$t2 = gettype($n2); // 'double'

$d = $n1 === $n2; // true