Memory Leak Using JSON

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I am new to JSON-C, Please see my sample code and let me know of it will create any memory leak, if yes then how to free JSON-C object.

    struct json_object *new_obj         = NULL;
    new_obj = json_tokener_parse(strRawJSON);
    new_obj = json_object_object_get(new_obj, "FUU");
    if(NULL == new_obj){
        SYS_OUT("\nFUU not found in JSON");
        return NO;
    }
    new_obj = json_object_object_get(new_obj, "FOO"); // I m re-using new_obj, without free it?  
    if(NULL == new_obj){
        SYS_OUT("\nFOO not found in JSON");
        return NO;
    }
    // DO I need to clean new_obj, if yes then how ??

Do I need to clean new_obj, if yes then how. Can some one help to understand how to do memory management JSON-C.

Thanks in Advance

c json memory-management memory-leaks json-c

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asked Jan 5 '12 at 16:39 Madhu S. Kapoor 13419

A quick web search seems to indicate that JSON-C uses reference counting to manage json_object instances and the function used to "free" the instances is json_object_put. –  hmjd Jan 5 '12 at 16:50

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2 Answers

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up vote 4 down vote

Yes, I believe your code will leak memory. The problem is that you are overwriting your new_obj pointer multiple times. Your code should be something like this:

struct json_object *new_obj, *fuu_obj, *foo_obj;
new_obj = json_tokener_parse(strRawJSON);
fuu_obj = json_object_object_get(new_obj, "FUU");
if(NULL == new_obj){
    SYS_OUT("\nFUU not found in JSON");
    return NO;
}
foo_obj = json_object_object_get(new_obj, "FOO"); 
if(NULL == new_obj){
    SYS_OUT("\nFOO not found in JSON");
    return NO;
}
json_object_put(foo_obj);
json_object_put(fuu_obj);
json_object_put(new_obj);

Please let me know if this works for you. If you want more help, json-c has a reference count mode which can give you more information about objects. Let me know and I can elaborate on this more.

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edited Mar 6 '12 at 3:51 Timothy Jones 10.5k22551

answered Mar 6 '12 at 3:41 portforwardpodcast 1,9841227

2

NO, We need to call json_object_put only once for root object as long as we are not explicitly allocating memory to json-object and this worked for me.....!! –  Madhu S. Kapoor Mar 12 '12 at 16:11

Yes actually you are right. You only need to call put one time for the root object! –  portforwardpodcast Apr 5 '12 at 18:05

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up vote 3 down vote accepted

NO, We need to call json_object_put only once for root object as long as we are not explicitly allocating memory to json-object and this worked for me.....!!