Matthias Kaeppler wrote:

Hello,

I have two questions regarding the proper use of boost::shared_ptr; both actually arose after reading http://www.boost.org/libs/smart_ptr/example/shared_ptr_example.cpp 2. In your examples, sometimes you're passing a shared_ptr by value, and sometimes by reference-to-const. Which is the better practice? Usually, common pointers are passed by value, but since in shared_ptr a reference counting mechanism keeps track of the copies, maybe it's better to pass it by reference whenever possible?

To sum up the costs (assuming raw pointer + count pointer impl): by ref: address-of push dword /de-ref per usage *on top of shared_ptr access*/ by val: de-ref incr push 2 dwords /normal usage/ de-ref decr As all of these are trivial CPU operations, both ways are very cheap, but since trivial usages will often be inlined, and complex usages in inner loops can be amortized (I've always wanted to say that :-) (the result of the reference de-ref or shared_ptr de-ref can be kept in a register), there can be /no/ difference in cost. So you're left with taste. Personally, I think a reference to a pointer is _always_ pretty ugly (but occasionally useful).