json-c库的使用

/ # cat /proc/meminfo 
MemTotal:          61632 kB
MemFree:           38796 kB
Buffers:               0 kB
Cached:            17104 kB
SwapCached:            0 kB
Active:             2152 kB
Inactive:          15476 kB
Active(anon):        524 kB
Inactive(anon):        0 kB
Active(file):       1628 kB
Inactive(file):    15476 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:             0 kB
SwapFree:              0 kB
Dirty:                 0 kB
Writeback:             0 kB
AnonPages:           548 kB
Mapped:             1184 kB
Slab:               4156 kB
SReclaimable:        820 kB
SUnreclaim:         3336 kB
PageTables:          100 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:       30816 kB
Committed_AS:       2476 kB
VmallocTotal:     956416 kB
VmallocUsed:      263600 kB
VmallocChunk:     686076 kB
/ # 

struct json_object* json_object_new_int(int32_t i)
{
	struct json_object *jso = json_object_new(json_type_int);
	if (!jso)
		return NULL;
	jso->_to_json_string = &json_object_int_to_json_string;
	jso->o.c_int64 = i;
	return jso;
}

static struct json_object* json_object_new(enum json_type o_type)
{
	struct json_object *jso;

	jso = (struct json_object*)calloc(sizeof(struct json_object), 1);
	if (!jso)
		return NULL;
	jso->o_type = o_type;
	jso->_ref_count = 1;
	jso->_delete = &json_object_generic_delete;
#ifdef REFCOUNT_DEBUG
	lh_table_insert(json_object_table, jso, jso);
	MC_DEBUG("json_object_new_%s: %p\n", json_type_to_name(jso->o_type), jso);
#endif /* REFCOUNT_DEBUG */
	return jso;
}

int json_object_object_add(struct json_object* jso, const char *key,
                           struct json_object *val)
{
	return json_object_object_add_ex(jso, key, val, 0);
}

int json_object_object_add_ex(struct json_object* jso,
	const char *const key,
	struct json_object *const val,
	const unsigned opts)
{
	struct json_object *existing_value = NULL;
	struct lh_entry *existing_entry;
	unsigned long hash;

	assert(json_object_get_type(jso) == json_type_object);

	// We lookup the entry and replace the value, rather than just deleting
	// and re-adding it, so the existing key remains valid.
	hash = lh_get_hash(jso->o.c_object, (const void *)key);
	existing_entry = (opts & JSON_C_OBJECT_ADD_KEY_IS_NEW) ? NULL : 
			      lh_table_lookup_entry_w_hash(jso->o.c_object,
							   (const void *)key, hash);

	// The caller must avoid creating loops in the object tree, but do a
	// quick check anyway to make sure we're not creating a trivial loop.
	if (jso == val)
		return -1;

	if (!existing_entry)
	{
		const void *const k = (opts & JSON_C_OBJECT_KEY_IS_CONSTANT) ?
					(const void *)key : strdup(key);
		if (k == NULL)
			return -1;
		return lh_table_insert_w_hash(jso->o.c_object, k, val, hash, opts);
	}
	existing_value = (json_object *) lh_entry_v(existing_entry);
	if (existing_value)
		json_object_put(existing_value);
	existing_entry->v = val;
	return 0;
}

const char* json_object_get_string(struct json_object *jso)
{
	if (!jso)
		return NULL;
	switch(jso->o_type)
	{
	case json_type_string:
		return get_string_component(jso);
	default:
		return json_object_to_json_string(jso);
	}
}
/* helper for accessing the optimized string data component in json_object
 */
static const char *
get_string_component(const struct json_object *jso)
{
	return (jso->o.c_string.len < LEN_DIRECT_STRING_DATA) ?
		   jso->o.c_string.str.data : jso->o.c_string.str.ptr;
}
/* backwards-compatible conversion to string */

const char* json_object_to_json_string(struct json_object *jso)
{
	return json_object_to_json_string_ext(jso, JSON_C_TO_STRING_SPACED);
}
const char* json_object_to_json_string_ext(struct json_object *jso, int flags)
{
	return json_object_to_json_string_length(jso, flags, NULL);
}

/* extended conversion to string */

const char* json_object_to_json_string_length(struct json_object *jso, int flags, size_t *length)
{
	const char *r = NULL;
	size_t s = 0;

	if (!jso)
	{
		s = 4;
		r = "null";
	}
	else if ((jso->_pb) || (jso->_pb = printbuf_new()))
	{
		printbuf_reset(jso->_pb);

		if(jso->_to_json_string(jso, jso->_pb, 0, flags) >= 0)
		{
			s = (size_t)jso->_pb->bpos;
			r = jso->_pb->buf;
		}
	}

	if (length)
		*length = s;
	return r;
}