Question

I’m trying to write a linked queue in C++, but I’m failing so far. I’ve created 2 files by now: my main.cpp and box.h. When trying to use my box, I receive the following message:

Description Resource Path Location Type
conversion from ‘Box*’ to
non-scalar type ‘Box’
requested main.cpp /QueueApplication line
14 C/C++ Problem

My code is as follows:

box.h

#ifndef BOX_H_
#define BOX_H_

template<class T>
class Box
{
public:
    Box(T value)
    {
        this->value = value;
        this->nextBox = NULL;
    }
    T getValue()
    {
        return this->value;
    }
    void setNext(Box<T> next)
    {
        this->nextBox = next;
    }
private:
    T value;
    Box<T> nextBox;
};

#endif /* BOX_H_ */

main.cpp

#include<iostream>
#include "box.h"

using namespace std;
int main(int argc, char** argv)
{
    Box<int> newBox = new Box<int>();
    cout << "lol";
    cin.get();
    cin.ignore();
    return 0;
}

Could you guys help me?

PS: before someone ask me why not to use stl … I’m in a data structures class.

Answer 1

The problem is with this line

Box<int> newBox = new Box<int>();

The new operator returns a pointer to a Box object created on the heap. The pointer will be of type Box<int>*. The left side of that expression declares a Box object. You can’t directly assign a pointer-to-X to an X. You should probably just omit the new keyword unless you have a reason to want to manage the storage lifetime of the object manually. Incidentally, I’m betting you come from Java, where new is always required to create objects. Not so in C++.

Also I think it’s awesome that your data structures class is introducing you to templates right off the bat.