C++ Moved-from state of most standard library classes


Example

C++11

All standard library containers are left in a valid but unspecified state after being moved from. For example, in the following code, v2 will contain {1, 2, 3, 4} after the move, but v1 is not guaranteed to be empty.

int main() {
    std::vector<int> v1{1, 2, 3, 4};
    std::vector<int> v2 = std::move(v1);
}

Some classes do have a precisely defined moved-from state. The most important case is that of std::unique_ptr<T>, which is guaranteed to be null after being moved from.