boost shared_ptr: difference between operator= and reset?

Question

Are there any differences between the two pieces of code below? Is any of them preferable to the other?

operator=

boost::shared_ptr<Blah> foo; // foo.ptr should be NULL
foo = boost::shared_ptr<Blah>(new Blah()); // Involves creation and copy of a shared_ptr?

reset

boost::shared_ptr<Blah> foo; // foo.ptr should be NULL
foo.reset(new Blah()); // foo.ptr should point now to a new Blah object

Note: I need to define the shared_ptr and then set it in a different line because I'm using it in a piece of code like:

boost::shared_ptr<Blah> foo;
try
{
  foo.reset...
}
foo...

Answer 1

operator= assigns a shared_ptr to a shared_ptr, while reset makes a shared_ptr take ownership of a pointer. So, basically there is no difference between the examples you have posted. That said, you should prefer neither of them and just use make_shared:

foo = boost::make_shared<Blah>();

Also, if possible, you can prevent having to declare a shared_ptr without initialization by wrapping the try-catch block in a separate function that simply returns a shared_ptr to the newly created object:

boost::shared_ptr<Blah> createBlah() {
    try {
        // do stuff
        return newBlah;
    }
    catch ...
}