Re: [boost] shared_ptr doesn't use unsigned reference count?

From: Darin Adler (darin_at_[hidden])
Date: 2001-10-24 00:20:54

on 10/23/01 5:14 PM, jeremy_at_[hidden] at jeremy_at_[hidden] wrote:

> Can anyone tell me why shared_ptr's pn member is not unsigned?

I'm aware of three reasons to use an unsigned long rather than a long in a C
or C++ program:

    1) to get predictable behavior from overflows and shifts
    2) to get an extra bit to accommodate larger numbers
    3) for clarity, when the value is always non-negative

In the case of shared_ptr, reason 1 does not apply. The 2^31 values that are
guaranteed by the C standard in a long are more than enough and 2^32 would
not be better, so reason 2 does not apply.

That leaves us with reason 3, clarity.

Many C and C++ programmers prefer to avoid the pitfalls of unsigned
arithmetic -- having the edge of the numeric range right next to 0 makes it
easier to write incorrect code. These programmers don't consider clarity
reason enough to use an unsigned type, and only use an unsigned integer type
when either reason 1 or 2 applies.

Let me turn your question around.

Can anyone tell me a practical advantage that would result from making
shared_ptr's pn member be unsigned?

    -- Darin