c++ - 模板类中的静态变量初始化

Question

谁能解释为什么这段代码会崩溃？使用 mingw 和 ubuntu 的两个窗口上的行为相同。

每个调试器传递给构造函数 One 的参数“a”被“优化掉”。

当我尝试访问静态成员 two_ 时发生崩溃；

三.h

#ifndef THREE_H
#define THREE_H
#include <string>

class One
{
public:
    One(const std::string& a)
        : a_(a)
    {

    }
    std::string a_;
};

template<typename P>
class Two : public One
{
public:
    Two()
        : One(P::name)
    {

    }
    std::string foo()
    {
        return a_;
    }
};

template<typename T>
class Three
{
public:
    struct Info
    {
        static std::string name;
    };
    typedef Two<Info> Two_t;
    static Two_t two_;
};

template < typename T >
std::string Three<T>::Info::name = std::string("aaaa");

template < typename T >
typename Three<T>::Two_t Three<T>::two_ = Three<T>::Two_t();


#endif // THREE_H

Answer 1

我相信你这里有一个 static initialization order fiasco 的实例.简而言之，您不能依赖于静态初始化程序的顺序。您应该考虑使用 construct on first use 模式(参见相同的链接，下面的一个问题)。

en.cppreference.com有以下要说的:

1) Unordered dynamic initialization, which applies only to (static/thread-local) class template data members that aren't explicitly specialized. Initialization of such static variables is indeterminately sequenced with respect to all other dynamic initialization. Initialization of such thread-local variables is unsequenced with respect to all other dynamic initialization.