Manually incrementing and decrementing a boost::shared_ptr?

Question

Is there a way to manually increment and decrement the count of a shared_ptr in C++?

The problem that I am trying to solve is as follows. I am writing a library in C

Answer 1

In your suggestion

The client will then be responsible to decrement the counter.

means that the client in question is responsible for memory management, and that your trust her. I still do not understand why.

It is not possible to actually modify the shared_ptr counter... (hum, I'll explain at the end how to...) but there are other solutions.

Solution 1: complete ownership to the client

Hand over the pointer to the client (shared_ptr::release) and expect it to pass the ownership back to you when calling back (or simply deleting the object if it is not really shared).

That's actually the traditional approach when dealing with raw pointers and it apply here as well. The downside is that you actually release ownership for this shared_ptr only. If the object is actually shared that might prove inconvenient... so bear with me.

Solution 2: with a callback

This solution means that you always keep ownership and are responsible to maintain this object alive (and kicking) for as long as the client needs it. When the client is done with the object, you expect her to tell you so and invoke a callback in your code that will perform the necessary cleanup.

struct Object;

class Pool // may be a singleton, may be synchronized for multi-thread usage
{
public:
  int accept(boost::shared_ptr