Question

I’m trying to pass a void* to a function, then inside that function make the pointer point to an dynamically created object. This is what I have so far but it doesn’t seem to be working:

main:

int main()
{
  void* objPtr;

  setPtr(objPtr);
}

setPtr:

void setPtr(void*& objPtr)
{
  objPtr = new Obj1; 
  (*objPtr).member1 = 10; //error: expression must have pointer-to-class type
}

Obj1:

struct Obj1
{
  int member1;
};

Thanks in advance

Answer 1

Well, sure: a void* doesn’t point to a class type, so can’t be used to access members. C++ is statically typed. The compiler sees a void* and that’s that. It won’t try to figure out what type of object the pointer actually points to — you have to tell it, with a cast:

objPtr->whatever; // fails: objPtr is not a pointer-to-class-type

((actual_type*)objPtr)->whatever; // okay: cast to actual_type*

Well, that’s the C programmer in me. Some folks prefer to use static_cast here:

static_cast<actual_type*>(objPtr)->whatever; // okay: cast to actual_type*

However you do it, though, you have to be sure that objPtr in fact points to an object of type actual_type.