Jansson - 用null属性解包json

Question

我在unpack json对象上遇到null值问题。 假设我们有：

/* root is the JSON object {"foo": null, "quux": true, "val" : null} */
const char *str;
int boolean;
int val = 0;
json_unpack(root, "{s:s, s:b, s:i}", "foo", &str, "quux", &boolean, "val", &val);

如何将“* str”指针指向null而val = 0而不是转入核心转储？