How can I recreate default arguments in C++ like in Python?

Question

I have this class in Python that I am trying to recreate in C++,

class Node:
    
    def __init__(self, data = None, next = None):
        self.data = data
        self.next= next

So far I have constructed this in C++, .h

#include<stdlib.h>
#include <iostream>

class Node {
    public:
        int value;
        Node* next;
        
        Node(int value, Node next) : value(0), next(NULL){
            std::cout << "inside .h" << "\n";
        };
};

and .cpp

Node::Node(int value, Node next) {
    this->value = value;
    this->next = &next;   
}

The code itself confuses me, it is usually best practice to avoid writing methods inside the .h but it wouldn't let me set the default values without {...}, i.e. I could not type Node(int value, Node next) : value(0), next(NULL); which I initially expected. It seems that I have defined two constructors aswell, which seems odd given the same parameters.

inside main it is not allowing me to instantiate an object as Node(5) etc...

Do we have a new way in C++ to mimic the Python class above?

Those aren't default values. Those are field initializers. You're completely ignoring the arguments. — user2357112
– user2357112, Commented Jun 30, 2021 at 5:28
I think you mean "how can I recreate default arguments in C++" — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Jun 30, 2021 at 5:28

rawrex · Accepted Answer · 2021-06-30 05:50:07Z

6

You do it the same way, by providing default arguments:

Node(int val = 0, Node* nxt = nullptr) : value(val), next(nxt) {}

This is both the default constructor, and the one that takes an int and a pointer to Node.

As a sidenote:

You may want to have the following form instead, adds flexibility:

Node(Node* nxt = nullptr, int val = 0) : next(nxt), value(val) {}

This way you can create (connect) a Node with default value:

Node n(&next_node); // a Node instance with default value 0

edited Jun 30, 2021 at 5:50

answered Jun 30, 2021 at 5:27

rawrex

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3 Comments

Joe Over a year ago

I am having a look at the link you provided but I can't seem to find where they talk about default arguments using the example(type x, type y): x(...), y(...)

rawrex Over a year ago

@Joe changed the link to a more appropriate one. Check the first paragraph.

Joe Over a year ago

oh, I see this is what the first comment meant, those are field initializers...

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