about C++ pointer

Question

Hi all, I have just started to practice c++ and I am stuck at one point. I have a Node class and the class has a constructor like this:

class Node
{
    public:
          Node(std::string,Node *,int,int,int,int);
    private:
          std::string state;
          Node* parent_node;
          int total_cost;
          int path_cost;
          int heuristic_cost;
          int depth;  
}

Node::Node(std::string state,Node *parent_node,int path_cost,int heuristic_cost,int total_cost,int depth)
{
 this->state=state;
 this->parent_node=parent_node;
 this->path_cost=path_cost;
 this->heuristic_cost=heuristic_cost;
 this->total_cost=total_cost;
 this->depth=depth;
}

Everything works ok so far, but I can not create a Node object with a NULL parent_node. I have tried this:

Node *n = new Node("state name",NULL,0,15,20,1);

I have also tried creating a new object and assigning it as parent_node, but no success either.

Node *temp = new Node();
Node *n = new Node("state name",temp,0,15,20,1);

I am doing something wrong with the pointer but I don't know what I am missing. I get a compile error which says no matching function call.

Thanks in advance

Answer 1

What environment are you working in? Compiler version?

Answer 2

Is your constructor public?

class Node
{
public:
    Node(std::string,Node *,int,int,int,int);
private:
    std::string state;
    Node* parent_node;
    int total_cost;
    int path_cost;
    int heuristic_cost;
    int depth;  
};

---

Also, don't forget the semicolon after Node declaration, this is not Java ;)

Answer 3

I think it's normal to specify 0 for a null pointer value, instead of NULL (NULL is a macro used for C which, depending on how the macro is defined, might not work well with C++).

Also, I don't like to see std::string as a parameter type. I'd prefer to see either const char*, or const std::string&.

Also Node* node = new Node(); will produce that compiler error, because when you declare a non-default constructor then you hide the default constructor (where by 'default constructor' I mean the constructor which takes no parameters). If you want to support new Node(); then you need to explicitly declare the default constructor (and, define how it's implemented.)

Answer 4

This works fine for me on GCC-4 on Mac OS X, after correcting the typos and implementing a Node::Node() constructor. It'd probably be helpful if you edited your question to include all the code to your test program, as well as the actual error messages you're getting when you compile.

Answer 5

The following compiles fine for me:

// Added this.
#include <string>


class Node
{    public:
          Node(std::string,Node *,int,int,int,int);
    private:
          std::string state;
          Node* parent_node;
          int total_cost;
          int path_cost;
          int heuristic_cost;
          int depth;
}; // Added semicolon here

Node::Node(std::string state,Node *parent_node,
           int path_cost,int heuristic_cost,int total_cost,int depth)
{
        this->state=state;
        this->parent_node=parent_node;
        this->path_cost=path_cost;
        this->heuristic_cost=heuristic_cost;
        this->total_cost=total_cost;
        this->depth=depth;
}

// Put code inside main.
int main()
{
    Node *n = new Node("state name",NULL,0,15,20,1);
}