dereferencing a void *

i use a void pointer to point either one of two distinct class types.

say:

class x{...}
class y{...}

and

void *p;
x object1;
y object2;

p = (x *)&object1;


etc....
and somehow when i need to reach to one of object1's fields:
i want to use p to reach the object but
i receive

"attempt to dereference a generic pointer" error?
is there anybody who has faced this error before?
thanks in advance:)

You have to typecast the void pointer to a pointer to the type you want to access.

so

*(x*)(p)

But you really should not have to deal with void pointers much in C++ because of templating and inheritance. void pointers are generally more necissary in C than C++.

yeah that was pretty much the same solution that i have tried
but it didn't work
you might be right about not using void * in C++

but does anyone has an advice to use what when i need to point two distict types via only one pointer.

(i'm implemeting a b+ tree and i need to point to internal nodes and leaf nodes with a unique type of pointer)

That should work. Make sure you encase that in parenthesis before you use it. You can use the arrow operator instead of dereferencing the cast pointer as well.

that's what i'm doing actually,
it's probably a property of C++ but i couldn't fix
let me be more informative:

class Int_Node{
public:
//internal node
vector<int> keys;
vector<void *> pointers;
};

class Leaf_Node{
public:
//leaf node
vector<int> records;
Int_Node *parent_node;
};

Leaf_Node bk2;
//......bk2 leaf has an internal node as the parent node
//then i want to reach the sibling leaf node

cout << ((Leaf_Node *)(bk2.parent_node->pointers[1]))->records[0];

//and this line of code gives the error
//i hope this code clearifies the problem

I can think of several solutions to your problem. What you are trying to do would be the first thing I would so as it is the easiest.

Example

Code:

---


int *i = new int;
char j[4] = "hi!!";

i = (int *)j; //casting a char array into an int pointer

//or for an object

struct a {
    int i;
};

struct b {
    char j[4];
    b() {
        std::memcpy(j, "hi!!", 4);
    }
};

a A;
b *B = (b *)&A;

((a *)b)->i = 6;

---

Get it? You may also want to make an abstract base class.

Quote:

---

Originally posted by pointing
i use a void pointer to point either one of two distinct class types.

---

Perhaps an abstract base class is a possible solution?

Quoting master5001
>int *i = new int;

Remember to delete...

delete i;

>char j[4] = "hi!!";

Needs to be five elements long for the terminating null

char* j = "hi!!";
char j[] = "hi!!";
char j[5] = "hi!!";

Quote:

---

Originally posted by Codulation
char* j = "hi!!";

---

Just watch out if you do that -- it's not the same as the other two. It creates a pointer to the first element of a string constant in the text area of your program while the other two examples you gave actually make an array with that data. In this case the data isn't being modified, but if you ever want to change the value of a letter then you'd most-likely get an error because you'd be trying to access a section of the programs memory that should not be being altered at runtime!

Thanks for clarifying that PolyOOP, That syntax can be used like a char array, but attempted modifications will have undefined results (most likely a seg fault).