Smart pointers in container like std::vector?
I am learning about smart pointers (std::auto_ptr) and just read here and here that smart pointers (std::auto_ptr) should not be put in containers (i.e. std::vector) because even most compilers won't complain and it might seem correct. There is no rule that says smart pointers won't be copied internally (by vector class for example) and transfer its ownership, then the pointer will become NULL. In the end, everything will be screwed up.
In reality, how often does this happen?
Sometimes I have vectors of pointers and if in the future I decide I want to have a vector of smart pointers what would my options?
I am aware of C++0x and Boost libraries, but for now, I would prefer to stick to a STL approach.
Answer
Yes, you really can't use std::auto_ptr with standard containers. std::auto_ptr copies aren't equivalent, and because standard containers (and algorithms) are allowed to copy their elements at will this screws things up. That is, the operation of copying a std::auto_ptr has a meaning other than a mere copy of an object: it means transferring an ownership.
Your options are:
- Use the Boost Smart Pointers library. This is arguably your best option.
- Use primitive pointers. This is fast and safe, so long as you manage the pointers properly. At times this can be complex or difficult. For example, you'll have to cope with (avoid) double-delete issues on your own.
- Use your own reference-counting smart pointer. That'd be silly; use a Boost Smart Pointer.