类和结构，没有默认构造函数

Question

I'm trying to build a Linked List who's elements are of my own specified type. Now I'm not going to lie I'm winging a lot of this having not had much experience with OOP in C++ but I'm stuck with a single error.

My LinkedList:

#include "Vehicle.h"
#include "string"
using namespace std;

class LinkedList
{
private:
    struct Node
    {
        Vehicle data;
        Node* next;
    };

    Node* root;
    int noofitems;

public:
    LinkedList();
    int getNoOfItems();
    Vehicle getItemByIndex(int index);
    void addItem(Vehicle itemIn);
    void deleteItem();
    void insertItem(Vehicle itemIn);
    ~LinkedList();
};

The Constructor and addItem()

LinkedList::LinkedList() : root(NULL), noofitems(0) {}

void LinkedList::addItem(Vehicle itemIn)
{
    Node* temp;
    temp = new Node();
    temp->data = itemIn;
    temp->next = this->root;
    this->root = temp;
}

My compiler is giving me this error: error C2512: 'LinkedList::Node' : no appropriate default constructor available . Now I've tried giving the struct a constructor like so:

struct Node
{
    Vehicle data;
    Node* next;
    Node() : next(NULL) {}
};

But then I get a new error on top of the old one: IntelliSense: no default constructor exists for class "Vehicle" . The word constructor is starting to look wrong and I'm really frustrated. Thanks In advance.

By the way if details of the vehicle class are needed:

class Vehicle
{

protected:
    string make;
    string model;
    string regNo;
    int engineSize;
    bool rented;

public:
    Vehicle(string makeIn, string modelIn, string regNoIn, int engineSizeIn);
    string getMakeModel(); // return two values concatinated
    string getRegNo();
    int getEngineSize();
    bool getRented();
    void setRented(bool rentedIn);
    ~Vehicle();
};

Vehicle::Vehicle(string makeIn, string modelIn, string regNoIn, int engineSizeIn) :
                make(makeIn), model(modelIn), regNo(regNoIn), engineSize(engineSizeIn),
                rented(false)
{}

string Vehicle::getMakeModel()
{
    return make + " " + model;
}

string Vehicle::getRegNo()
{
    return regNo;
}

int Vehicle::getEngineSize()
{
    return engineSize;
}

bool Vehicle::getRented()
{
    return rented;
}

void Vehicle::setRented(bool rentedIn)
{
    rented = rentedIn;
}

Vehicle::~Vehicle(){}

Answer 1

Node has a member of type Vehicle . Since you cannot default construct a Vehicle the default constructor for Node is marked as deleted. You will need to provide your own default constructor that constructs the Vehicle member to some state like

struct Node
{
    Vehicle data;
    Node* next;
    Node() : data("", "", "", 0), next(nullptr) {}
};

or provide a default constructor for Vehicle like

class Vehicle
{
    //...
public:
    Vehicle() = default;
    //...
};

Answer 2

The error is self explanatory. You have not explicitly initialized vehicle in your Node class as shown:

struct Node
{
    Vehicle data;
    Node* next;
    Node() : next(NULL) {} // NO initialization for vehicle
};

The compiler will try and then construct a Vehicle using it's default constructor, but it finds none. In your vehicle class you have defined a constructor taking arguments:

Vehicle(string makeIn, string modelIn, string regNoIn, int engineSizeIn);

Thus the compiler will not generate one for you. To fix this you can either define a default constructor yourself, or you can declare one with the word default which will force the compiler too generate one: