On 08/11/2015 10:27 AM, TONGARI J wrote:

template<class T>
struct wrapper
{
     wrapper() = default;

     wrapper(boost::intrusive_ptr<T> const& p) : _p(p) {}

     boost::intrusive_ptr<T> const& get_ptr() const
     {
#if 0
         // This is OK.
         if (_p)
             return _p;
         return nullptr;
#else
         // Strange behavior.
         return _p ? _p : nullptr;
#endif
     }

In both cases, you return a reference to a temporary, incurring undefined behavior.