如何在C ++中将const FB :: variant＆转换为用户定义的类？

Question

I am tryintg to cast const FB::variant& sample into SampleJS* in C++. like this:

SampleJS* info = sample.cast<SampleJS*>();

i do not know what is going wrong here. this gives me error of:

boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::bad_any_cast> > 

Thank you in advance.

Answer 1

You need to understand that FB::variant just stores whatever type is put into it. Your code will absolutely work... if what is inside happens to be a MouseInfoJS*. However, you'd have to go through a lot of work to put something like that inside, since the FB::variant class is designed to make it difficult, but not impossible, to store inside it types that it doesn't know.

So basically, what you're trying to do probably doesn't make any sense, so you can't do it.

Depending on what type MouseInfoJS is, it might sorta make sense. Does MouseInfoJS inherit from JSAPI? (or JSAPIAuto?) If so, then it would somewhat make sense to try what you're doing, except that you'd never have a MouseInfoJS*, you'd have a MouseInfoJSPtr, which would be a typedef for boost::shared_ptr, since it would then be partially owned by the page and thus dangerous to store a raw pointer there.

Even in this case, which you'd need to use .convert_cast<MouseInfoJSPtr> , not .cast , it won't work on most modern browsers because they wrap the NPObject returned by FireBreath in another object which doesn't allow us to get the original object back; I believe this is a security feature. For more information, see A firebreath JSAPI will not be recognized in firefox