Question

I saw in couple of tree codes that a function of tree class has both * and & with node
for example to insert a node in a BST a function is like this

insertnode(node * &t,string value)
{
t = new node; t-> val = value 
// code to find right place in BST
}

I wish to know why we pass reference to pointer in general and also in particular to this case . Please also mention if there is any other scenario of this ,Thanks

Instead of posting another question .
Can someone also point out the use of object class ? i mean using instances of object class did it allocate all the memory gone for all sub classes ? i.e int float etc. etc.

Answer 1

Pointers, as any other variables, are passed by value, unless you specify you want to pass it by reference.

void foo(int* x)
{
   x = new int[1];
}

void goo(int*& x)
{
   x = new int[1];
}

int* x = NULL;
foo(x);
//x is NULL here, and you also have a memory leak
goo(x);
//x points to an array of 1 int

In your case, you pass a reference to a pointer because you want to modify the original pointer. Modifying a pointer doesn’t mean changing the value it points to, but changing the address to which it points to.