C++ anonymous struct pointer assignment

Question

So no, this is not the best way to do things. However, for the sake of theory, how would one successfully assign a pointer value to a pointer of an anonymous struct?

#pragma pack(push,1)
    struct
    {
        __int16 sHd1;
        __int16 sHd2;
    } *oTwoShort;
#pragma pack(pop)

    oTwoShort = (unsigned char*)msg; // C-Error

produces:

error C2440: '=' : cannot convert from 'unsigned char *' to '<unnamed-type-oTwoShort> *'

The example assumes msg is a valid pointer itself.

Is this possible? Since you don't have an actual type, can you even typecast?

Answer 1

You can get the type with decltype:

oTwoShort = reinterpret_cast<decltype(oTwoShort)>(msg);

This was added in C++11 though, so it won't work with older compilers. Boost has an implementation of roughly the same (BOOST_PROTO_DECLTYPE) that's intended to work with older compilers. It has some limitations (e.g., if memory serves, you can only use it once per scope) but it's probably better than nothing anyway.

Answer 2

I think you have to use C++11's decltype:

oTwoShort = reinterpret_cast<decltype(oTwoShort)>(msg);

Answer 3

reinterpret_cast<unsigned char*&>(oTwoShort) = reinterpret_cast<unsigned char*>(msg);

But, really?

Answer 4

As said you can't do a pointer cast but you can do this:

memcpy(&oTwoShort,&msg,sizeof(void*));