提升c ++属性 - 如果key不存在则设置为false

Question

I am new to json parsing with boost using the property tree.

If I have this hash:

foo = {'test1',true}

ptree pt;
bool v = pt.get<bool>("test2");

I need to check a key exists and if not set it to false.

How do I do that gracefully?

Thanks

Answer 1

  // bool optional
  boost::optional<bool> v = pt.get_optional<bool>("test2");

  // any type actually
  boost::optional<std::string> v2 = pt.get_optional<std::string>("test3");

  if (v) // key exists
    bool bool_value = v.get();
  else // not exists
    v.set(false);

Answer 2

From boost documentation you can try to find the key and if not_found() then you can push a new key.

assoc_iterator not_found() ; Returns the not-found iterator. Equivalent to end() in a real associative container.

const_assoc_iterator not_found() const; Returns the not-found iterator. Equivalent to end() in a real associative container.

assoc_iterator find(const key_type & key) ; Find a child with the given key, or not_found() if there is none. There is no guarantee about which child is returned if multiple have the same key.

const_assoc_iterator find(const key_type & key) const; Find a child with the given key, or not_found() if there is none. There is no guarantee about which child is returned if multiple have the same key.