c++ - 因shared_ptr而崩溃

Question

有人可以向我解释一下为什么会在这里崩溃吗？

#include <memory>
#include <functional>

struct Teacher : std::enable_shared_from_this<Teacher> {
    struct Timetable;
    std::shared_ptr<Timetable> timetable;
    Teacher (int n) : timetable(std::make_shared<Timetable>(*this, n)) {}
};

struct Period {
    std::shared_ptr<Teacher> teacher;
    Period (const std::shared_ptr<Teacher>& t) : teacher(t) {}
};

struct Teacher::Timetable {
    Teacher& teacher;
    std::shared_ptr<Period> homeForm;
    Timetable (Teacher& t, int n) : teacher(t),  // Assume something is done with n.
        homeForm( std::make_shared<Period>(teacher.shared_from_this()) ) {}  // Crashes.
//      homeForm( std::make_shared<Period>(std::shared_ptr<Teacher>(&teacher)) ) {}  // Also crashes.
};

int main() {
    std::shared_ptr<Teacher> teacher = std::make_shared<Teacher>(3);
}

不是 teacher.shared_from_this()自std::shared_ptr<Teacher> teacher起允许在这里已经是shared_ptr了吗？如果没有，我该如何初始化homeForm正确吗？

Answer 1

问题是您的代码调用 shared_from_this之前std::shared_ptr<Teacher>已全面建成。从某种程度上来说，Teacher 是有道理的。子对象必须在智能指针完全构造之前构造。

如果你像这样改变代码，

struct Teacher : std::enable_shared_from_this<Teacher> {
    struct Timetable;
    std::shared_ptr<Timetable> timetable;
    Teacher() {}
    void init(int n) { this->timetable = std::make_shared<Timetable>(*this, n); }
};

// Everything else unchanged

int main() {
    std::shared_ptr<Teacher> teacher = std::make_shared<Teacher>();
    teacher->init(3);
}

它会运行良好。

请注意，我不建议将此作为重构。构造函数应尽可能完全初始化对象。看看你的代码，在我看来，你可能想考虑更激进地重新构建它。您真的需要所有这些交叉引用共享指针吗？