Parsing deeply nested JSON key using json-c

Question

I'm using the json-c library , and after reviewing the documentation, I couldn't find a way to get at a deeply nested key/value without using a bunch of loops, here's what I've tried:

json_object_object_foreach(json_data_obj, key, val) {
  printf("KEY:%s\t VAL:%s\n", key, json_object_to_json_string(val));
  /* TODO: Traverse the JSON
   * "results" => "channel" => "item" => "condition" => "temp"
   */
}

Here's the output:

KEY:query        VAL:{ "count": 1, "created": "2015-04-10T06:05:12Z", "lang": "en-US", "results": { "channel": { "item": { "condition": { "code": "33", "date": "Thu, 09 Apr 2015 9:55 pm PDT", "temp": "56", "text": "Fair" } } } } }

How can I get the temp value without using json_object_object_foreach() macro several times?

Answer 1

Meanwhile (since json-c 0.13) one can reach deeply nested object by walking the object tree with the json_c_visit function.

int json_c_visit (
    json_object * jso,
    int future_flags,
    json_c_visit_userfunc * userfunc,
    void * userarg 
)   

The function walks to every object of the json document and calls the user defined function userfunc . One can also steere the traveling through the tree with returnvalues of the userfunc. Take theunittests and the expected output as examples how to use the function.

Answer 2

You'll likely have to call json_object_object_get_ex for each object until you get to the key/value pair that you want, checking for the existence of each key along the way.

There may be another way, but this is what I've had to do on a recent project working equally complex JSON data.

The following code assumes b contains your JSON string.

json_object *json_obj, *results_obj, *channel_obj, *item_obj, *condition_obj,*temp_obj;
int exists;
char *temperature_string;

json_obj = json_tokener_parse(b); 
exists=json_object_object_get_ex(json_obj,"results",&results_obj);
if(exists==false) { 
  printf("\"results\" not found in JSON"); 
  return; 
} 
exists=json_object_object_get_ex(results_obj,"channel",&channel_obj); 
if(exists==false) { 
  printf("key \"channel\" not found in JSON"); 
  return; 
} 
exists=json_object_object_get_ex(channel_obj,"item",&item_obj); 
if(exists==false) { 
  printf("key \"item\" not found in JSON"); 
  return; 
}
exists=json_object_object_get_ex(item_obj,"condition",&condition_obj); 
if(exists==false) { 
  printf("key \"condition\" not found in JSON"); 
  return; 
}
exists=json_object_object_get_ex(condition_obj,"temp",&temp_obj); 
if(exists==false) { 
   printf("key \"temp\" not found in JSON"); 
   return; 
}
temperature_string = json_object_get_string(temp_obj); //temperature_string now contains "56"