Is there a way to check if its safe to copy or assign an object in C++?

Question

I have the following problem. I'm using the C library igraph (http://igraph.sourceforge.net/) in a program I must do in c++. So I found a c++ wrapper of this C library (http://code.google.com/p/igraphhpp/) that provides some nice interface I wanted to use, in a class called Graph.

I have the following class in my program:

class Agent 
{
private: 
  double beta;  
  Graph * innerGraph;
public:
  Agent(int N, double beta_) {
    innerGraph = new Graph;
    *innerGraph = Graph::full(N);
    beta = beta_;
  };
  ~Agent() {delete innerGraph;}
  void MCStep();
};

The function MCStep() must do the following:

• make a copy of the Graph contained in *innerGraph,
• do some stuff to this copy, without altering the original,
• check if the altered copy satisfy some condition and, if yes, update *innerGraph with this new modified graph.

If I knew that the library implements a safe copy constructor, I'd do it in the obvious way, but I don't. How can I check it?

Answer 1

Check the source of Graph, see whether the copy constructor calls this function:

http://igraph.sourceforge.net/doc/html/ch04s02s01.html#igraph_copy

There's no general way - the C++ language itself knows nothing about "deep copies" or "shallow copies", so copy constructors are all the same to it as far as that's concerned. In an ideal world, anyone publishing a C++ wrapper like this would document it, and in this case probably should make it a complete deep copy.

Answer 2

Since you're working with pointers to Graph, can't you just swap the pointers in step 3? (Don't forget to delete the temporary after swap)