关于节点指针分配的困惑

Question

My code looks like this:

#include <iostream>

struct Node {
   double data;
   Node* next;
};

int main(){
   Node* a;
   a = new Node;
}

I am having a hard time understanding why the assignment would work for a pointer. Because a is type Node* but the new node is type Node .

At the beginning of my class, I was taught that pointer assignment needs to always be an address.

For example:

int * x;
int y = 5;

This would be allowed:

x = &5;

But this wouldn't:

x = y;

So, by that same logic, shouldn't the assignment of Node* a; be:

a = &(new Node);

Instead of:

a = new Node;

?

Answer 1

When you call new , it creates a new object and returns a pointer to that object. It is quite common to store that pointer in a pointer variable. You would use & new(...) if it returned a reference to the newly-created object. But it doesn't.

Answer 2

but the new Node is type Node.

is absolutely wrong. This is not Java. new Node returns a pointer to a freshly allocated on heap Node.

Answer 3

First of all, every assignment requires correct type . Either you provide left argument of the exact same type as the variable you assign to, or of a type you can convert from. Eg

int x = 5; //here x is a type of int and 5 is also an int

or

double w = 3; //here w is a type of double and 3 is again int but int can be converted to double

in contrary

int z = 3.2; //won't compile because 3.2 is a float and floats have to be explicitly casted to ints.

Now, with your code, Node* is a type you read as Node pointer and new allocates memory on heap, creates new object and return its address which in this case is also Node pointer . Types match and everything works.