Question

I am writing some code to implement a deep copy of an object.

Here is my code:

//---------------------------------------------------------------------------

#pragma hdrstop

#include <tchar.h>
#include <string>
#include <iostream>
#include <sstream>
#include <conio.h>

using namespace std;

//---------------------------------------------------------------------------

class Wheel
{
public:
    Wheel() : pressure(32)
    {
        ptrSize = new int(30);
    }
    Wheel(int s, int p) : pressure(p)
    {
        ptrSize = new int(s);
    }
    ~Wheel()
    {
        delete ptrSize;
    }
    void pump(int amount)
    {
        pressure += amount;
    }
    int getSize()
    {
        return *ptrSize;
    }
    int getPressure()
    {
        return pressure;
    }
private:
    int *ptrSize;
    int pressure;
};

class RacingCar
{
public:
    RacingCar()
    {
        speed = 0;
        *carWheels = new Wheel[4];
    }
    RacingCar(int s)
    {
        speed = s;
    }
    RacingCar(RacingCar &oldObject)
    {
        for ( int i = 0; i < sizeof(carWheels)/sizeof(carWheels[0]); ++i)
        {
            Wheel oldObjectWheel = oldObject.getWheel(i);
            carWheels[i]=new Wheel(oldObjectWheel.getSize(),oldObjectWheel.getPressure());
        }
    }
    void Accelerate()
    {
        speed = speed + 10;
    }
    Wheel getWheel(int id)
    {
        return *carWheels[id];
    }
    void printDetails()
    {
        cout << carWheels[0];
        cout << carWheels[1];
        cout << carWheels[2];
        cout << carWheels[3];
    }
private:
    int speed;
    Wheel *carWheels[4];
};

#pragma argsused
int _tmain(int argc, _TCHAR* argv[])
{

RacingCar testCar;
testCar.printDetails();

RacingCar newCar = testCar;
newCar.printDetails();

getch();
return 0;
}
//---------------------------------------------------------------------------

For some reason, my C++ builder crashes after compiling this code. Is there anything above that is not correct that would cause this to crash. There is no compile error, the program just crashes.

Answer 1

The problem is:

Wheel *carWheels[4];

and

*carWheels = new Wheel[4];

this only allocates 4 Wheels for carWheels[0]. Along with

return *carWheels[id];

If id is not 0, this will lead to undefined behavior because, as previously stated, only the first element is a valid pointer.

Besides this, the code is horrible. Avoid raw pointers. There are much better alternatives in C++. Use std::vector or std::array where you’d use a C-array, and smart pointers where you’d use raw ones.