c++ - 了解 C++ 重构语法

Question

我们可以在对象创建后再次调用它的构造函数吗？

#include <iostream>

struct A
{
    A ( ) { std::cout << "A::A" << std::endl; }
    ~A ( ) { std::cout << "A::~A" << std::endl; }
};

int main( )
{
    A a;
    a.~A();    // OK
    a.A::A();  // OK in Visual Studio 2005, 2008, 2010

    return 0;
}

Answer 1

你不应该像这样调用构造函数，作为成员函数调用。原因是 (n3242, 12.1/2):

A constructor is used to initialize objects of its class type. Because constructors do not have names, they are never found during name lookup; however an explicit type conversion using the functional notation (5.2.3) will cause a constructor to be called to initialize an object.

如果你真的真的想在应该是对象的东西上调用构造函数——除非在非常特殊的情况下你不应该这样做——你可以使用调用构造函数的 placement new:

new (&a) A();