c++ - When a boost::shared_ptr might not be freed? -

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afer reading topic c++ interview preparation (matt's answer) i've got question boost::shared_ptr. possible shared_ptr leak memory? how?

shared_ptr uses reference counts, , means circular references can cause leaks. concretely:

struct {     shared_ptr<a> other; };  shared_ptr<a> foo() {     shared_ptr<a> one(new a);     shared_ptr<a> two(new a);     one->other = two;     two->other = one;     return one; }

the data structure returned foo never deallocated without manual intervention (set either of other pointers null).

now fact every programmer should know; more interesting interview conversation it. options include:

  • redesigning data structure pointer cycles not necessary;
  • demoting @ least 1 pointer in every cycle non-owning reference (a bare pointer or weak_ptr);
  • a dedicated cycle collector;
  • as last resort, manually nulling out pointers @ appropriate points (this breaks exception safety).

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