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From: Mikko <mikko.levanto@iki.fi>
Newsgroups: comp.lang.c
Subject: Re: Which newsgroup for json parsing?
Date: Sat, 18 May 2024 16:21:52 +0300
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On 2024-05-16 18:01:15 +0000, Josef Möllers said:

> On 16.05.24 18:27, Mikko wrote:
>> On 2024-05-08 13:04:56 +0000, Josef Möllers said:
>> 
>>> 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.
>>> 
>>> Thanks in advance,
>> 
>> Sometimes it is easier to make a parser than to use an existing one.
>> In this case I might try LEX.
>> 
> 
> Sorry to be nitpicking, but lex is a "lexical analyzer" aka a 
> "scanner", it can only recognize tokens, eg the brackets, quotes, 
> identifiers etc, but not structures.
> "yacc" (or its "bison" equivalent" would be a parser but definitely too heavy.
> 
> What one could do would be to use LEX to recognize the tokens and the 
> write a recursive descent parser in plain C.

As YACC is too heavy I would use only LEX and do with C what LEX alone
cannot do. I havn't often done so but when I did I got what I wanted.
For JSON parsing a stack of partly parsed objets and arrays is sufficient
in addition to what LEX gives, so the C code can be kept simple. LEX
can put C fragment to the right place in the final code.

If a generic parser is not needed but only a parser with specific structures
known in advance the result of parsing can be delivered in a form that is
easier to use than a result from a generic JSON parser. In addition, the
LEXä+C code can simpler in some sense although more complicated in another
sense.

> But, as I wrote in another posting, I have switched to libjson-c5 and 
> the code works fine.

That the code works fine is the most important aspect.

-- 
Mikko