应该 std::unique_ptr<void>被允许

Should std::unique_ptrlt;voidgt; be permitted(应该 std::unique_ptrvoid被允许)

问题描述

这是一个非常简单的问题.考虑以下代码:

This is a very simple question. Consider the following code:

#include <iostream>
#include <memory>

typedef std::unique_ptr<void> UniqueVoidPtr;

int main() {
    UniqueVoidPtr p(new int);
    return 0;
}

使用 cygwin (g++ 4.5.3) 和以下命令编译 g++ -std=c++0x -o prog file.cpp 工作得很好.但是，使用 Microsoft 编译器(VS 2010 或 2013)进行编译时出现此错误:

Compiling with cygwin (g++ 4.5.3) with the following command g++ -std=c++0x -o prog file.cpp works just fine. However, compiling with the microsoft compiler (either VS 2010 or 2013) I get this error:

C:Program Files (x86)Microsoft Visual Studio 10.0VCINCLUDEmemory(2067) : error C2070: 'void': illegal sizeof operand
        C:Program Files (x86)Microsoft Visual Studio 10.0VCINCLUDEmemory(2066) : while compiling class template member function 'void std::default_delete<_Ty>::operator ()(_Ty *) const'
        with
        [
            _Ty=void
        ]
        C:Program Files (x86)Microsoft Visual Studio 10.0VCINCLUDE	ype_traits(650) : see reference to class template instantiation 'std::default_delete<_Ty>' being compiled
        with
        [
            _Ty=void
        ]
        C:Program Files (x86)Microsoft Visual Studio 10.0VCINCLUDEmemory(2193) : see reference to class template instantiation 'std::tr1::is_empty<_Ty>' being compiled
        with
        [
            _Ty=std::default_delete<void>
        ]
        foo1.cpp(7) : see reference to class template instantiation 'std::unique_ptr<_Ty>' being compiled
        with
        [
            _Ty=void
        ]

这是预期的吗?我正在写一个类，我想在类中拥有一个唯一的指针.在尝试为类计算移动构造函数的语义时，我遇到了这个问题(我假设是因为我最终正确编码了移动构造函数:即其他错误已修复).

Is this expected? I'm writing a class where I wanted to have a unique pointer in the in the class. While trying to work out the semantics of a move constructor for the class, I ran into this (I assume because I finally got my move constructor coded correctly: i.e. the other errors were fixed).

推荐答案

MSVC 是对的，而 GCC 是错的:

MSVC is right while GCC is wrong:

标准(3.9/5):

不完全定义的对象类型和void类型是不完全类型

Incompletely-defined object types and the void types are incomplete types

标准(20.7.1.1.2/4):

Standard(20.7.1.1.2/4):

如果 T 是不完整类型，则程序格式错误

If T is an incomplete type, the program is ill-formed

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