C++不要在構(gòu)造函數(shù)或析構(gòu)函數(shù)中調(diào)用虛函數(shù)的原因是什么

到目前為止，被調(diào)用的函數(shù)應(yīng)該只屬于構(gòu)造對象本身，而不是可能存在于派生類中的某個(gè)覆蓋函數(shù)。那樣做非常難理解。最壞的情況，在構(gòu)造函數(shù)或者析構(gòu)函數(shù)中直接或間接調(diào)用一個(gè)沒有實(shí)現(xiàn)的純虛函數(shù)會導(dǎo)致沒有定義的行為。

class Base {
public:
    virtual void f() = 0;   // not implemented
    virtual void g();       // implemented with Base version
    virtual void h();       // implemented with Base version
    virtual ~Base();        // implemented with Base version
};

class Derived : public Base {
public:
    void g() override;   // provide Derived implementation
    void h() final;      // provide Derived implementation

    Derived()
    {
        // BAD: attempt to call an unimplemented virtual function
        f();

        // BAD: will call Derived::g, not dispatch further virtually
        g();

        // GOOD: explicitly state intent to call only the visible version
        Derived::g();

        // ok, no qualification needed, h is final
        h();
    }
};

注意：調(diào)用一個(gè)特定的限定函數(shù)不是虛調(diào)用，即使這個(gè)函數(shù)是虛函數(shù)。

See also factory functions for how to achieve the effect of a call to a derived class function without risking undefined behavior.

參考工廠函數(shù)以便了解如何達(dá)成調(diào)用派生類功能的效果而不必承擔(dān)引起未定義行為的風(fēng)險(xiǎn)。

There is nothing inherently wrong with calling virtual functions from constructors and destructors. The semantics of such calls is type safe. However, experience shows that such calls are rarely needed, easily confuse maintainers, and become a source of errors when used by novices.

從構(gòu)造函數(shù)和析構(gòu)函數(shù)中調(diào)用虛函數(shù)并不是本身有什么錯(cuò)誤。這種調(diào)用的語義是安全的。然而，經(jīng)驗(yàn)表明這樣的調(diào)用很少是必須的，很容易擾亂維護(hù)者，如果被新手使用會成為錯(cuò)誤源。

• Flag calls of virtual functions from constructors and destructors.

• 提示來自構(gòu)造函數(shù)或析構(gòu)函數(shù)的虛函數(shù)調(diào)用。