c++ - 在从 void* 转换和返回时混合静态和重新解释转换是否不安全？

Question

简单地说:如果我将 static_cast 类型 X* 转换为 void*，reinterpret_cast 是否总是安全的它回到 X*？

我无法提供任何失败的案例，例如:

#include <iostream>

struct a
{
    int* m_array;
};

int main()
{
    bool fail = false;

    for(int i = 0; ++i < 5000;)
    {
        a* pA = new a;
        pA->m_array = new int [i+1]; // A new size of data everytime
        pA->m_array[i] = 10;

        void* pvA = static_cast<void*>(pA);
        pA = reinterpret_cast<a*>(pvA);

        if(pA->m_array[i] != 10)
        {
            fail = true;
            break;
        }

        delete []pA->m_array;
        delete pA;
    }

        if(fail)
            std::cout<<"FAILED!!";
        else
            std::cout<<"Never failed :/";
}

Link to compiled example

在 vs 2012 的调试和 Release模式下给出结果“Never failed :/”。然而，这很可能是未定义的行为。对吧？

Answer 1

定义明确。根据 ISO/IEC 14882:2011 [expr.reinterpret.cast]§7(强调我的):

An object pointer can be explicitly converted to an object pointer of a different type. When a prvalue v of type “pointer to T1” is converted to the type “pointer to cv T2”, the result is static_cast<cv T2*>(static_cast<cv void*>(v)) if both T1 and T2 are standard-layout types (3.9) and the alignment requirements of T2 are no stricter than those of T1, or if either type is void.