Question

Say I have an array of void pointer pointing to objects of different types and I want to pass them through a function and cast them to pointers of their respective type, how would I go about doing this? I’ve tried this current code, but I get error:

‘void*’ is not a pointer-to-object type

objectA myObjectA;
objectB myObjectB;
objectC myObjectC;
objectD myObjectD;

void *data[4];

data[0] = static_cast<void *>( &myObjectA );
data[1] = static_cast<void *>( &myObjectB );
data[2] = static_cast<void *>( &myObjectC );
data[3] = static_cast<void *>( &myObjectD );

void dereference( void *data )
{
    objectA *objA_ptr = static_cast<objectA *>( data[0] );
    objectB *objB_ptr = static_cast<objectB *>( data[1] );
    objectC *objC_ptr = static_cast<objectC *>( data[2] );
    objectD *objD_ptr = static_cast<objectD *>( data[3] ); 
}

Anyone know the correct way to implement this?

edit: For context, I’m using opencv and trying to create a simple gui interface with a trackbar. Opencv allows for userdata to be fed into the TrackbarCallback which is called when the slider is moved, but only in the form of a void pointer.

 int createTrackbar( const string& trackbarname, const string& winname,
                           int* value, int count,
                           TrackbarCallback onChange=0,
                           void* userdata=0); 

Answer 1

Say I have an array of void pointer

void deference( void *data )

That’s not an array of void pointers, it’s a single void pointer.

Change that to void **, and then since you’re mixing C and C++ styles up anyway, why not just use a C style cast? :

objectA *objA_ptr = (objectA *) data[0];