php json_decode returning infinite

Question

If I run the following, no error is returned and the value of $result is INF. json_last_error() returns 0.

$result = json_decode('547533e683433', true);

As this is a string and not JSON I would expect $result to be NULL and json_last_error() to return 4 or JSON_ERROR_SYNTAX.

Why is this happening?

I would expect json_last_error() to return an error code, in this case it should be 4 (JSON_ERROR_SYNTAX) and the $result to be NULL. I'll update the question. — greg
– greg, Commented Jun 11, 2015 at 21:11
@greg: According to the docs, [PHP] will also encode and decode scalar types and NULL. So it's trying to decode '547533e683433' as an int, but it's so big that it gives you infinity. — gen_Eric
– gen_Eric, Commented Jun 11, 2015 at 21:13
Why the down votes? It seems like a legitimate question to me? @RocketHazmat your answers have been great, add as an answer and I'll accept. — greg
– greg, Commented Jun 11, 2015 at 21:22

gen_Eric · Accepted Answer · 2015-06-11 21:32:58Z

3

This is the expected result. While '547533e683433' is not valid JSON, PHP can still "decode" it.

PHP implements a superset of JSON as specified in the original RFC 4627 - it will also encode and decode scalar types and NULL.

According to the docs for json_decode, PHP will decode single scalar values, not just arrays/objects.

In the case of '547533e683433', it's interpreted as an int when decoding (strings need to be in double quotes). 547533e683433 is read as 547533 x 10^683433 (see the docs for is_numeric), which is a huge number. PHP can't represent a number this big, so it gives you INF.

answered Jun 11, 2015 at 21:32

gen_Eric

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