Newb C++ Class Problem

Question

I am trying to get a grasp on pointers and their awesomeness as well as a better C++ understanding. I don't know why this wont compile. Please tell me what is wrong? I'm trying to initialize the pointer when an instance of the class is created. If I try with a normal int it works fine but when I tried to set it up with a pointer i get this in the console

Running…

Constructor called

Program received signal: “EXC_BAD_ACCESS”.

sharedlibrary apply-load-rules all

Any assistance is appreciated greatly.

Here is the code

#include <iostream> 
using namespace std;
class Agents
{
public:
    Agents();
    ~Agents();
    int getTenure();
    void setTenure(int tenure);
private:
    int * itsTenure;
};
Agents::Agents()
{
    cout << "Constructor called \n";
    *itsTenure = 0;
}
Agents::~Agents()
{
    cout << "Destructor called \n";
}
int Agents::getTenure()
{
    return *itsTenure;
}
void Agents::setTenure(int tenure)
{
    *itsTenure = tenure;
}
int main()
{
    Agents wilson;
    cout << "This employees been here " << wilson.getTenure() << " years.\n";
    wilson.setTenure(5);
    cout << "My mistake they have been here " << wilson.getTenure() <<
             " years. Yep the class worked with pointers.\n";
    return 0;
}

Answer 1

You are just missing a new, in the constructor.

 itsTenure = new int;

You don't need to make this a pointer, however. Why are you?

Answer 2

You need to allocate memory for *tenure in the constructor:

Agents::Agents()
{
    cout << "Constructor called \n";
    itsTenure = new int;
    *itsTenure = 0;
}

Answer 3

You don't ever create the int that the pointer points to, so the pointer is pointer to an area of memory that doesn't exist (or is used for something else).

You can use new to get a block of memory from the heap, new returns the address of the memory location.

itsTenure = new int;

So now itsTenure holds the memory location you can dereference it to set its value.

The changed constructor is as follows:

Agents::Agents()
{
    cout << "Constructor called \n";
    itsTenure = new int;
    *itsTenure = 0;
}

But you must also remember to delete it using delete

Agents::~Agents()
{
    cout << "Destructor called \n";
    delete itsTenure;
}

Answer 4

You have to allocate a block of memory for your int, and only then use the address of this block of memory (the pointer). This is done with new :

cout << "Destructor called \n";   
itsTenure = new int;    
*itsTenure = 0;

Then you have to release the memory in the destructor with delete:

    cout << "Destructor called \n";
    delete itsTenur;

Answer 5

*itsTenure = 0 does not initialize the pointer. It writes 0 to the location that itsTenure points to. Since you never specified where itsTenure points to, that might be anywhere and the behaviour is undefined (an access violation like you're getting being the most likely result).