3
Node* node;    
*node = nullptr;

Report an error：

error: no viable overloaded '='
       *node = nullptr;

but

Node* node;    
*node = NULL;

is correct ?

lyzMaster
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5 Answers5

5

Most likely a Node can be constructed with an int. Since null is defined as an int constant equal to 0, so you wrongly call the node constructor and assign it to the node.

As Sid S said, node = nullptr is the right expression.

Guillaume Racicot
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5

NULL is most likely an old macro, inherited from the C world, and defined 0.

So what is happening in the second case is assigning the number 0 to a variable of type Node. Whereas in the first case a pointer (nullptr) is assigned. The compiler knows for sure that this is wrong, since *node is not a pointer. Which means it will complain.

Whether it will complain for assigning a numeric 0 to Node will depend if the assignment operator for Node has been overloaded to accept a number. Or whether there is an implicit conversion/constructor from a number to Node.

Matthias247
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3

Neither one is correct. You should use node = nullptr; to assign to the node variable, as opposed to assigning to what node is pointing to.

Sid S
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2

So:

Node* node;    
*node = nullptr;

cannot be done because, you are trying to assign pointer to type Node, what you should do is:

Node* node;    
node = nullptr;

You have to understand when you declare pointer you use following sintax:

int *n = 5;
n = nullptr;

where as following is

int *n = 5;
*n = 3;

*n is de-referencing pointer, and going to the address n points to. Same is true with in your Node example. Meanwhile *node = NULL might be implementation dependent. So Node type might have something like this:

Node& operator = (const Node &n ) { 
    if (n == NULL) {
        // do something
    }

    // do something else
    return n;
}
0

You should use node=nullptr;

You have made a pointer and now have to allocated the pointer to point to something, therefore node=nullptr;

Node * nullptr; defines the type of the variable nullptr is , it is a pointer to type node

Sam
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