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++?…
Best Answer
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: