Program stops - move array to function | C++ - c++

Question

I have 2 classes.
First Class - Midgam - The constructor has the following line:
midgam = new Vector[20];
The second class - Vector - where I create an array named array.
The program works great just that I have a little problem.
At the end of the program I try to print in alphabetical order, I use the BubbleSort sorting. The sorting works fine but something in the Swap function stops.
This is how it looks:
void Midgam::Swap(Vector *xp, Vector *yp) {
Vector temp = *xp;
cout << temp.getName() << endl;
*xp = *yp;
*yp = temp;
}
void Midgam::bubbleSort() {
int i, j;
for (i = 0; i < iterator - 1; i++) {
for (j = 0; j < iterator - i - 1; j++) {
if (midgam[j].getName().compare(midgam[j+1].getName()) > 0) {
Swap(&midgam[j], &midgam[j+1]);
}
}
}
}
I work with Visual Studio, the program stops and the program shows me the following code snippet in the Vector class:
Vector::~Vector() {
if (array)
delete[] array;
}
full definitions of Midgam:
#include <iostream>
#include <string>
#include "Vector.h"
using namespace std;
#ifndef MIDGAM_H_
#define MIDGAM_H_
class Midgam {
private:
int boxNum;
int maxParties;
int iterator;
Vector *midgam;
public:
Midgam(int num_of_boxes, int num_of_parties);
virtual ~Midgam();
void Start();
void Menurmal();
void SumOfEzor();
double SumOfParty(string name);
int SumAllVotes();
void AddParty();
void Swap(Vector *xp, Vector *yp);
void bubbleSort();
void Histograma();
void PrintStars(int num);
int FindPartyByName(string party);
void PrintAll();
};
#endif /* MIDGAM_H_ */
full definitions of Vector:
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
#ifndef VECTOR_H_
#define VECTOR_H_
class Vector {
private:
string name;
int size;
unsigned int *array;
bool Bool;
public:
Vector(string name, int size);
Vector();
Vector & operator=(const Vector &);
virtual ~Vector();
bool StringToArray(string str);
bool getBool();
string getName();
unsigned int getAddress();
int getSize();
unsigned int getValueFromArray(int index);
double sumOfArray();
void PrintArray();
};
#endif /* VECTOR_H_ */
Does anyone know why it does not work? Thank you

Answer 1

Your Vector lacks a proper copy constructor.
Vector temp = *xp;
//NOT EQUAL TO:
//Vector temp;
//temp=*xp;
The above statement won't call operator=(const Vector &) even though there's an equal sign. The following line is correct and equivalent:
Vector temp(*xp);
The reason is that this is a copy initialization - temp is created and so a constructor must be called - in particular the copy constructor Vector(const Vector &). Which you did not explicitly declared and so a default one was used.
Then a shallow copy is made, temp and *xp then share the same array and when both their destructors get called the second one will try to delete already deleted memory - undefined behavior which triggers Visual Studio's debugger (at least in debug mode).
The solution is to do a proper deep copy - create a new array and copy its contents:
#include <algorithm> #Contains std::copy_n
Vector::Vector(const Vector& other)
{
name=other.name;
size=other.size;
//Creates a new array
array= new unsigned int[size];
//Copies the array contents
std::copy_n(other.array,size,array);
Boo=other.Bool;
}
Also this is a prime example of why not to use raw memory. I get that you are implementing custom vector and don't want to use std::vector for the array but at least use std::unique_ptr. If you would have just done that you wouldn't have to ask this question in the first place as the compiler would have complained and the debugger wouldn't have to do the compiler's job.