Copy hashtable to another hashtable using c++

Question

I am starting with c++ and need to know, what should be the approach to copy one hashtable to another hashtable in C++?

We can easily do this in java using: HashMap copyOfOriginal=new HashMap(original);

But what about C++? How should I go about it?

UPDATE

Well, I am doing it at a very basic level,perhaps the java example was a wrong one to give. This is what I am trying to implement using C++:

I have this hash array and each element of the array is the head of a linked list. Which has it's individual nodes (data and next pointer).

And now, I need to copy the complete hash array and the linked list each node is pointing to.

Answer 1

Whichever hashmap you're using, I'm sure it has a copy-constructor and possibly operator=.

hashmap_type newMap = oldMap; // copies

And that's it. C++ has no standard hash map, though.

Answer 2

In C++ you would use either the copy constructor or simple assignment (with values) to perform this.

For example

std::map<int,string> map1 = CreateTheMap();
std::map<int,string> map2 = map1; 
std::map<int,string> map3(map1);

Answer 3

I am afraid, somehow, that you are using a custom HashMap class, since you speak about its implementation details.

In C++, when it comes to copying a class, there is a special purpose Copy Constructor, which syntax looks like:

class Foo
{
public:
  Foo(); // regular constructor

  Foo(const Foo& rhs); // copy constructor
};

It can be invoked with either syntax:

Foo copy(original);
Foo copy2 = original;

Now, if you HashMap does not provide a copy constructor, my first suggestion is to switch to an existing implementation, like boost::unordered_map or if available std::hash_map, std::tr1::hash_map or std::tr1::unordered_map. The reasons there are so may std:: possibilities is that many STL features a hash_map long before it was standardized. unordered_map is here to stay though, and the boost one too.

If you can't switch you are bound to implement the copy operation somehow.