Boost json_parser警告C4715

Question

I'm trying to save some data from string in boost::property_tree:ptree object:

const char* data = "Here are json params";
boost:property_tree:ptree tr;
std::stringstream ss;
ss << data;

//Here i get warning
boost::property_tree:ptree::read_json(ss, tr);

Warning is following:

boost\property_tree\detail\json_parser\standard_callbacks.hpp(132): warning C4715: 'boost::property_tree::json_parser::detail::standard_callbacks<boost::property_tree::basic_ptree<std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::basic_string<char,std::char_traits<char>,std::allocator<char> >,std::less<std::basic_string<char,std::char_traits<char>,std::allocator<char> > > > >::new_tree' : not all control paths return a value

Can anyone help me fix this problem?

Answer 1

It isn't a problem. It has to do with Boost, not your code. You can ignore the warning or suppress it in your IDE if you wish. The error is Ptree& new_tree technically can finish without a return statement. Here's the code:

Ptree& new_tree() {
    if (stack.empty()) {
        layer l = {leaf, &root};
        stack.push_back(l);
        return root;
    }

    layer& l = stack.back();

    switch (l.k) {
        case array: {
                l.t->push_back(std::make_pair(string(), Ptree()));
                layer nl = {leaf, & l.t->back().second};
                stack.push_back(nl);
                return *stack.back().t;
            }

        case object:
        default:
            BOOST_ASSERT(false); // must start with string, i.e. call new_value

        case key: {
                l.t->push_back(std::make_pair(key_buffer, Ptree()));
                l.k = object;
                layer nl = {leaf, &l.t->back().second};
                stack.push_back(nl);
                return *stack.back().t;
            }

        case leaf:
            stack.pop_back();
            return new_tree();
    }
}

As you can see, in the switch there's a default: BOOST_ASSERT(false) which means while the function doesn't return anything, it also triggers your debugger to immediately stop because something went horribly wrong. Your compiler isn't clever enough to figure it by itself, so it warns you. In this case you can definitely ignore the warning.

Answer 2

The function contains a switch with one case being

        default:
            BOOST_ASSERT(false); // must start with string, i.e. call new_value

Arguably this part doesn't return a value, but mostly because it doesn't return at all.