Library function returns raw pointer and I want to use smart pointer

Question

I have this situation where the library I use has many functions that return raw pointers to objects, how could I now use boost smart pointers in my program using this library and using smart pointers?

The library is xerces-C++ and an example is getting the document iterator:

boost::shared_ptr<DOMNodeIterator> itera = document->createNodeIterator(rootelement, DOMNodeFilter::SHOW_ALL, NULL, true);

The createNodeIterator function returns a pointer to a DOMNodeIterator object, this is a raw pointer and therefore cannot be cast just like that to a boost::shared_ptr... How would I best deal with this? Use raw pointers instead?

Answer 1

I guess the library provides a way of releasing those raw pointers ?

If so, you can just "create" a shared_ptr with a custom deleter, specifying the "free function" provided by the library.

Example:

If you have the two functions:

Foo* createFoo();
void freeFoo(Foo* foo);

You can create a shared_ptr that way:

boost::shared_ptr<Foo> foo(createFoo(), freeFoo);

If the raw pointer is not meant to be released, you can instead provide a "null-deleter" that does nothing when the reference counter reaches 0.

Answer 2

You can change boost::shared_ptr<DOMNodeIterator> itera = document->createNodeIterator(rootelement, DOMNodeFilter::SHOW_ALL, NULL, true); to boost::shared_ptr<DOMNodeIterator> itera( document->createNodeIterator(rootelement, DOMNodeFilter::SHOW_ALL, NULL, true)); and it should compile fine.

Answer 3

If you are creating the object locally use boost::scoped_ptr instead of boost:shared_ptr as this is very dangerous if you pass as a parameter to some other function. If you are dealing with shared_ptr, you have think about object reference count as well.

If you use Scoped_ptr, it automatically deletes when scope of the object ends.

Class Foo boost::scoped_ptr objfoo(new Foo());