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I want to xor my instance pointer (size_t) with some sort of value from a member function pointer from it, but the compiler doesn't like

reinterpret_cast<std::size_t>(MemberFunctionPointer)

which otherwise works fine on a regular function pointer. Is there any way I can pull some sort of unique value from a member function pointer to xor with the object it's from for a hash?

I suppose this is me being ignorant about the underlying difference between a standard function pointer and a member function pointer... I will do some more research on that. However, I would still like some way to get some sort of "size_t" value from a member function pointer - or any kind of value I can turn into a size_t and use to create a unique hash value.

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  • I suppose you need to give it as [object_instance].MemberFunctionPointer (square brackets not in your code) although the whole concept seems dubious to me. Commented Nov 25, 2015 at 14:17
  • That is not guaranteed by the standard to work with regular non-member function pointers either (but it does work on many common implementations). If the member function is not static, then I'm fairly certain that you can't achieve what you want without diving deep into how your compiler implements member functions. Commented Nov 25, 2015 at 14:21
  • @o_weisman I don't understand... these function pointers don't point to a memory address that is set in stone like a regular pointers? Can't I get the address they're pointing at to see if two of them are pointing at the same thing? Commented Nov 25, 2015 at 14:24
  • You can achieve what you want with some template magic; you'll need an instance of the class though to achieve this .. however, could you instead test for type equality of the objects? If the objects are the same (i.e. if (typeid(x) == typeid(some_class)) { .. }) then the member functions are the same for the types .. ? Commented Nov 25, 2015 at 15:19
  • @Simple Ugh... should have tried to cast to const... I couldn't cast member pointer to void*, and being inexperienced in C++ I didn't even think that const void* would make a difference. Commented Nov 25, 2015 at 15:37
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