将tr1 :: function强制转换为void *

Question

I have the following tr1::function prototype that I am trying to cast to a void*:

typedef std::tr1::function<cv::Mat (const cv::Mat,const void*)> preprocessingFunc;

In this function I am storing it in a vector that contains structures denoting the type of function and the pointer to the function:

void ImageGraph::addNode(preprocessingFunc func)
{
    NodeFunction nodeFunction = { typeid(func), (void*)func };
    //nodes.push_back(nodeFunction);
}

The error I get:

ImagePipeline.cpp: In member function 'void IP::ImageGraph::addNode(IP::preprocessingFunc)': ImagePipeline.cpp:32: error: invalid cast from type 'IP::preprocessingFunc' to type 'void*' /usr/include/c++/4.2.1/typeinfo:135: error: 'std::type_info::type_info(const std::type_info&)' is private ImagePipeline.cpp:32: error: within this context

Is it possible to cast this function type to a pointer (void*)? If not, is there a better way to achieve what I am doing?

For clarity I am storing function pointers to call at later dates, and their are currently 3 types of function pointers, however I would like to store them all in the same vector.

Answer 1

A pointer to a member function can not be stored in a function pointer, because, essentially, a member function has a hidden argument (the "this" pointer).

There are two solutions: Either a real "pointer to member function" (which requires the correct type of function pointer), or make the function static, and pass in the object itself as a pointer (eg a void).

To me, this seems like kind of an odd solution, and I would think there are better solutions, such as using an interface class, and add your interface objects as "nodes", perhaps?

For a bit more on "pointer to member function", have a look here: http://www.parashift.com/c++-faq/fnptr-vs-memfnptr-types.html

But given the comment below, you are actually trying to store an object in a pointer. That's similar to (void *)3.1415926; - it doesn't make sense. You probably shouldn't use void * here, but something else, such as pointer to function<> [and change your addNode to take a pointer to a preprocessingFunc object].

Answer 2

You're approaching it from the wrong end, it seems. Why are you using void* ? You state that you have " currently 3 types of function pointers". To store callable things, use tr1::function<> . It can be initialized from most reasonable sources: function pointers, bound pointers to member functions, functors, and obviously other tr1::function s