shared_ptr 崩溃

Question

谁能给我解释一下为什么会崩溃？

#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);
}

这里不允许 teacher.shared_from_this() 因为 std::shared_ptr<Teacher> teacher 已经是 shared_ptr 了吗？如果没有，我该如何正确初始化 homeForm？

Answer 1

问题是您的代码在 std::shared_ptr<Teacher> 完全构建之前调用了 shared_from_this。在智能指针完全构造之前必须构造 Teacher 子对象在某种程度上是有道理的。

如果你这样修改代码，

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);
}

它会运行没问题。

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，在我看来你可能想要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？

shared_ptr 崩溃

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