c++ - Does moving an element from an STL container remove it from that container? -

c++ - Does moving an element from an STL container remove it from that container? -

i have foobar class sayhello() method outputs "well hello there!". if write next code

vector<unique_ptr<foobar>> foolist; foolist.emplace_back(new foobar()); unique_ptr<foobar> myfoo = move(foolist[0]); unique_ptr<foobar> myfoo2 = move(foolist[0]); myfoo->sayhello(); myfoo2->sayhello(); cout << "vector size: " << foolist.size() << endl;

the output is:

well hello there! hello there! vector size: 1

i'm confused why works. shouldn't foolist[0] become null when first move? why myfoo2 work?

here's foobar looks like:

class foobar { public: foobar(void) {}; virtual ~foobar(void) {}; void sayhello() const { cout << "well hello there!" << endl; }; };

shouldn't foolist[0] become null when first move?

yes.

why myfoo2 work?

it doesn't; causes undefined behaviour. compiler happens produce code doesn't crash if utilize null pointer phone call non-virtual function doesn't dereference this.

if alter function follows, clearer what's happening:

void sayhello() const { cout << "well hello there! address " << << endl; } hello there! address 0x1790010 hello there! address 0 vector size: 1

c++ visual-studio-2010 stl move-semantics