CODEWITHSUNDEEP
cjsonlibjson
MOHAMED
MOHAMED

Reputation: 43578

How to free json_object?

I have the following code

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

#include <json/json.h>

int main(int argc, char **argv)
{
      json_object *new_obj;
      char buf[] = "{ \"foo\": \"bar\", \"foo2\": \"bar2\", \"foo3\": \"bar3\" }";
      new_obj = json_tokener_parse(buf);
      .....
      json_object_put(new_obj);
}

Does the json_object_put(new_obj) free all memory related to new_obj ?

Upvotes: 13

Views: 16747

Answers (2)

Andrew Hodel
Andrew Hodel

Reputation: 35

You have to understand how the library works.

json_tokener_parse() is first, and it creates an object that will act as a memory managing parent that all objects which are created from it use to access the data they define.

So if you get all the way down to making a char *str for a string field, that field doesn't actually store the string, the original object returned from json_tokener_parse() does.

This is the reason that you can't just use a normal free() and expect things to work as if it was a char array or something.

To be safe, don't use the json_tokener_parse_ex() function because you will have to also free the object that is the tokener, with json_tokener_parse() you don't need that argument.

Beyond that, to safely close everything just do:

while (json_object_put(orig_object) != 1) {
  // keep freeing
}

You should only need to do that once, but the library may change.

Upvotes: -1

djechlin
djechlin

Reputation: 60818

From the documentation:

void json_object_put    (struct json_object *this)

Decrement the reference count of json_object and free if it reaches zero

Source: http://oss.metaparadigm.com/json-c/doc/html/json__object_8h.html

Upvotes: 8

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