json_object_object_foreach : Browse through every json object

You can browse through every json object using the macro json_object_object_foreach

The syntax

json_object_object_foreach(obj,key,val)

where obj is the json object you want to parse, key and value correspond to key: value pairs. As mentioned before, json_object_object_foreach is a macro defined something like this

#define json_object_object_foreach(obj,key,val) \
char *key; struct json_object *val; \
for(struct lh_entry *entry = json_object_get_object(obj)->head; ({ if(entry) { key = (char*)entry->k; val = (struct json_object*)entry->v; } ; entry; }); entry = entry->next )

So key, val are not some variables, but you can choose any random strings to correspond to key and value

The following program depicts this

#include <json/json.h>
#include <stdio.h>

int main() {
 char * string = "{\"sitename\" : \"joys of programming\",\
 \"tags\" : [ \"c\" , \"c++\", \"java\", \"PHP\" ],\
 \"author-details\": { \"name\" : \"Joys of Programming\", \"Number of Posts\" : 10 } \
 }";
 json_object * jobj = json_tokener_parse(string);
 enum json_type type;
 json_object_object_foreach(jobj, key, val) {
 printf("type: ",type);
 type = json_object_get_type(val);
 switch (type) {
 case json_type_null: printf("json_type_null\n");
 break;
 case json_type_boolean: printf("json_type_boolean\n");
 break;
 case json_type_double: printf("json_type_double\n");
 break;
 case json_type_int: printf("json_type_int\n");
 break;
 case json_type_object: printf("json_type_object\n");
 break;
 case json_type_array: printf("json_type_array\n");
 break;
 case json_type_string: printf("json_type_string\n");
 break;
 }
 }
}

Now let’s compile the program

$ gcc json_object_object_foreach.c  -l json
json_object_object_foreach.c: In function ‘main’:
json_object_object_foreach.c:9: error: ‘for’ loop initial declarations are only allowed in C99 mode
json_object_object_foreach.c:9: note: use option -std=c99 or -std=gnu99 to compile your code

Oh, there are some errors, as you can see. This can be resolved by the option -std=c99

gcc json_object_object_foreach.c  -ljson -std=c99

Let’s execute the program

$ ./a.out
type: json_type_string
type: json_type_array
type: json_type_object

This program is not generic in nature. It has not shown the details of “author-details“. But you can write a recursive function to go through all the elements using json_object_object_foreach.

Tags: json parsing, json-c tutorial, json_object_object_foreach, libjson, libjson tutorial