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From: jak <nospam@please.ty>
Newsgroups: comp.lang.c
Subject: Re: Which newsgroup for json parsing?
Date: Thu, 9 May 2024 15:18:11 +0200
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Josef Möllers ha scritto:
> 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,
> 
> Josef

   Hi,
   from your post I can't understand if you are writing
   production code or just for yourself, nor if you intend to
   deepen your knowledge of json or just acquire the data of
   interest from the json. If you are interested in the data and
   the code is for you, I can suggest an inelegant but effective
   way unless you want to monitor the data in a fast loop. I
   would suggest you let the jq command line do the work for
   you and grab its output via popen. jq is a command for *nix
   but you can also find it for windows. here is an example:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <locale.h>

int main()
{
     FILE *fp;
     char from_plug[] = "{\"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}}";
     char echo_fmt[] = "cmd /c echo %s | jq 
..temperature.tC,.voltage,.source";
     size_t cmd_len = snprintf(NULL, 0, echo_fmt, from_plug) + 1;
     char cmd[cmd_len];
     double temp, volt;
     char source[20];

     snprintf(cmd, cmd_len, echo_fmt, from_plug);

     if((fp = popen(cmd, "r")) != NULL)
     {
         fscanf(fp, " %lf %lf %*[\"]%[^\"] ", &temp, &volt, source);
         setlocale(LC_ALL, "");
         wprintf(L"\n"
                 L"temperature: %6.2lf\u00B0\n"
                 L"voltage:     %6.2lf v\n"
                 L"source:      %hs\n", temp, volt, source);
         pclose(fp);
     }
     else
         perror("popen");

     return 0;
}


output:

temperature:  41.10°
voltage:     237.90 v
source:      button