Re: Which newsgroup for json parsing?

On 08/05/2024 14:04, Josef Möllers wrote:

Hi all,
 I am trying to parse a json string received through MQTT from a "Shelly Plug S", e.g.
{"id":0, "source":"button", "output":true, "apower":0.0, "voltage":237.9, "current":0.000, "aenergy":{"total":0.000,"by_minute":[0.000,0.000,0.000],"minute_ts":1715172119},"temperature":{"tC":41.1, "tF":106.0}}
 I am trying to use libjson-glib but I can't figure out what to use as the first argument to json_gobject_from_data()!
I am also looking at libjson-c but cannot find any examples that could guide me.
 

JSON parsing is the sort of thing you can easily do in C, but you really don't want to do yourself, becuase it is a lot of fiddly code to write, and everyone wants to solve exactly the same problem, which is to query text formatted as JSON, usually for fields whose names and types are known, but with facilities to list fields onthe fly.
But of course I wrote my own JSON parser in C++, As programmers often do. But it was at work, so I can't post a copy here, since it was work for hire and not mine to give away.
Now libjson-glib strikes me as rather a poorly designed library with too many dependencies, and over complicated.
But here's the prototype for the function
  GObject*
json_gobject_from_data (
   GType gtype,
   const gchar* data,
   gssize length,
   GError** error
)
Obviously, this creates a Gobject* that you query, from text that you pass in (he data argument). For some reason the string is not nul-terminated and so you pass in the length, and you also get a parse error object, and to be fair this can be extremely important.
But what is the gtype parameter?
WEll a bit of digging reveals this palaver
GType
my_struct_get_type (void)
{
   static GType boxed_type = 0;
   if (boxed_type == 0)
     {
       boxed_type =
         g_boxed_type_register_static (g_intern_static_string ("MyStruct"),
                                       (GBoxedCopyFunc) my_struct_copy,
                                       (GBoxedFreeFunc) my_struct_free);
       json_boxed_register_serialize_func (boxed_type, JSON_NODE_OBJECT,
                                           my_struct_serialize);
       json_boxed_register_deserialize_func (boxed_type, JSON_NODE_OBJECT,
                                             my_struct_deserialize);
     }
   return boxed_type;
}
So you set it up. Ir's a highly flexible way of registering a data structure at run time. But not what you want to parse a bit of JSON. And if there's a simple default type to pass in, they are not documenting this clearly. So if I had a choice, I would simply avoid the library and choose another.
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