Deserializing NaN

[rdilipk]

I am dealing with some Json that is sending down NaN quoted like this: "NaN". The Json::Value::asDouble() method fails because the type of that entity is being deserialized as string and calling asDouble() on that expectedly throws. I am using 0.7.0. Two questions:

1. How should I handle these correctly? Should I ask upstream code to NOT quote the word NaN given that Json can't describe such entities anyway? They do send out null (no quotes) and asDouble successfully deserializes them to 0.

2. I see something called allowSpecialFloats which looks like what I want but it is buried under some class called OurFeatures (mirroring Features). That in turn is hidden inside json_reader.cpp. Don't I have access to that setting?

( I see this has been brought up before: #209
How do I make use of that fix?)

[BillyGoto]

On Fri, Mar 18, 2016 at 11:20 AM, rdilipk [email protected] wrote:

I am dealing with some Json that is sending down NaN quoted like this:
"NaN". The Json::Value::asDouble() method fails because the type of that
entity is being deserialized as string and calling asDouble() on that
expectedly throws.

If you quote it, it's a string, not a double. Nothing can be done about
that.
Sometimes people want to send the word "NaN" as a string.
We can't have special string values. There's no NaN number in JSON
http://www.json.org/, and them's the breaks.

Two questions:

1. How should I handle these correctly? Should I ask upstream code to NOT
   quote the word NaN given that Json can't describe such entities anyway?
   They do send out null (no quotes) and asDouble successfully deserializes
   them to 0.

This null -> 0.0 conversion is an amenity I wouldn't feel safe relying on.
You should always check isDouble() before calling asDouble().

2. I see something called allowSpecialFloats which looks like what I want
   but it is buried under some class called OurFeatures (mirroring Features).
   That in turn is hidden inside json_reader.cpp. Don't I have access to that
   setting?

Yes. It's described in the json/reader.h header, as a public Json::Value
member (unfortunately, IMO).

ǝnɥɐuop ʎllıq

[rdilipk]

On Fri, Mar 18, 2016 at 11:29 AM, BillyGoto [email protected]
wrote:

On Fri, Mar 18, 2016 at 11:20 AM, rdilipk [email protected]
wrote:

Two questions:

1. How should I handle these correctly? Should I ask upstream code to NOT
   quote the word NaN given that Json can't describe such entities anyway?
   They do send out null (no quotes) and asDouble successfully deserializes
   them to 0.

This null -> 0.0 conversion is an amenity I wouldn't feel safe relying on.
You should always check isDouble() before calling asDouble().

The thing is, the Json I am dealing with itself has some meta-data that advertises the
data types of values I am dealing with. It says I have to expect an array of DOUBLE
values (which is why I don't have to do isDouble()). Most values are indeed
of the right type but some are null and others are "NaN" (quoted like a string). I
guess your point is ask them to send NaN (UNQUOTED), just like null and Jsoncpp will do
something meaningful with it?

2. I see something called allowSpecialFloats which looks like what I want
   but it is buried under some class called OurFeatures (mirroring
   Features).
   That in turn is hidden inside json_reader.cpp. Don't I have access to
   that
   setting?

Yes. It's described in the json/reader.h header, as a public Json::Value
member (unfortunately, IMO).

Sorry. I am a bit confused. I currently use Json::Reader to 'parse' in the entire Json
document as plain text. I then process it in a way I want. As far as I can see there
is no way to set allowSpecialFloats here. I must now use CharReaderBuilder to create a
CharBuilder just to operate on a fragment of Json?

[BillyDonahue]

Yeah, Json::Reader is deprecated.
https://github.com/open-source-parsers/jsoncpp/blob/master/include/json/reader.h

\deprecated Use CharReader and CharReaderBuilder.

So:

Json::CharReaderBuilder builder;
builder["collectComments"] = false;
std::unique_ptr<Json::CharReader> reader(builder.newCharReader());

... now use this reader.

[rdilipk]

That works! Thank you very much! I somehow totally missed the deprecation notice.

[cdunn2001]

2. I see something called allowSpecialFloats which looks like what I want
   but it is buried under some class called OurFeatures (mirroring Features).
   That in turn is hidden inside json_reader.cpp. Don't I have access to that setting?

Yes. It's described in the json/reader.h header, as a public Json::Value member (unfortunately, IMO).

allowSpecialFloats is kinda weird, but configurable parsing and dumping is one of the major advantages of JsonCpp over other libraries.

[BillyDonahue]

On Saturday, March 19, 2016, Christopher Dunn [email protected]
wrote:

2. I see something called allowSpecialFloats which looks like what I want
   but it is buried under some class called OurFeatures (mirroring Features).
   That in turn is hidden inside json_reader.cpp. Don't I have access to that
   setting?

Yes. It's described in the json/reader.h header, as a public Json::Value
member (unfortunately, IMO).

allowSpecialFloats is kinda weird, but configurable parsing and dumping
is one of the major advantages of JsonCpp over other libraries.

I like the configurability. I just mean the configurability mechanism is a
little loose. It's a little too freeform for me. An API to set options by
const identifiers would make it more clear what the supported operations
are, and keep the underscore-named data member out of user code. Exposing
a data member makes it hard to change the representation.

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#447 (comment)

[cdunn2001]

True, but I don't have time to change that (if you mean to add methods to the Builder for everything). If you submit a PR, you can merge it. My main concern is easy and obvious binary compatibility.