By default unmapped members in a JSON document are skipped. There are a few ways to turn this into an error.

Global parser option

One can change the default for all classes as a parser option. For example with from_json it would loook similar to:

 ++
daw::json::from_json<Foo>( 
   json_doc1, 
   daw::json::options::parse_flags<
       daw::json::options::UseExactMappingsByDefault::yes>
   );

When the value is set to yes, you can exclude a class from this by adding a type alias to it's class mapping called ignore_unknown_members. For example:

 ++
namespace daw::json {
    template<>
    struct json_data_contract<Foo> {
        using ignore_unknown_members = void;
        
        using type = json_member_list<json_number<"bar", int>>;
        
        //...
    };
}

Enabling per class

To enable errors for unknown members per class, add a type alias to the mapping called exact_class_mapping

 ++
namespace daw::json {
    template<>
    struct json_data_contract<Zaz> {
        using exact_class_mapping = void;
        
        using type = json_member_list<json_number<"foo", int>>;
        //...
    };
}