I have recently discovered that when I have pointers within a class, I need to specify a Copy constructor.
To learn that, I have made the following simple code. It compiles, but gives me runtime error when performing the copy constructor.
I am trying to copy just the value from the pointer of the copied object, but avoiding assigning the same address.
So, what's wrong here?
class TRY{
public:
TRY();
~TRY();
TRY(TRY const &);
int *pointer;
void setPointer(int);
};
void TRY::setPointer(int a){
*pointer = a;
return;
}
TRY::TRY(){}
TRY::~TRY(){}
TRY::TRY(TRY const & copyTRY){
int a = *copyTRY.pointer;
*pointer = a;
}
int main(){
TRY a;
a.setPointer(5);
TRY b = a;
b.setPointer(8);
cout << "Address of object a = " << &a << endl;
cout << "Address of object b = " << &b << endl;
cout << "Address of a.pointer = " << a.pointer << endl;
cout << "Address of b.pointer = " << b.pointer << endl;
cout << "Value in a.pointer = " << *a.pointer << endl;
cout << "Value in b.pointer = " << *b.pointer << endl;
return 0;
}
I'll be using this concept for other classes with lots of pointers in it, where I need to copy all values from on object to the other. Copying is initially necessary for this code, so I would like to keep the copying possibility (I won't be hiding the copy constructor as private).
Besides, the real class I need to implement has like 10 pointers, and it might be changing with time. Isn't there a somewhat smarter way to have a deep copy constructor in C++?...
With the statement int* pointer
you have just defined a pointer but has not allocated any memory. First you should make it point to a proper memory location by allocating some memory like this: int* pointer = new int
. Then in the copy constructor again you have to allocate the memory for the copied object. Also, don't forget to release the memory using delete in the destructor.
I hope this example helps:
class B
{
public:
B();
B(const B& b);
~B();
void setVal(int val);
private:
int* m_p;
};
B::B()
{
//Allocate the memory to hold an int
m_p = new int;
*m_p = 0;
}
B::B(const B& b)
{
//Allocate the memory first
m_p = new int;
//Then copy the value from the passed object
*m_p = *b.m_p;
}
B::~B()
{
//Release the memory allocated
delete m_p;
m_p = NULL;
}
void B::setVal(int val)
{
*m_p = val;
}