引用已删除的析构函数 [英] Referencing deleted destructor

问题描述

我有以下代码:

struct Foo
{
    int type;
    union
    {
        int intValue;
        double doubleValue;
        std::wstring stringValue;
    } value;
};

，然后在cpp文件中，我有:

and then in the cpp file I have:

std::vector<Foo> row;
some_class_object->func( row );

然后我得到了

error C2280: 'void *Foo::__delDtor(unsigned int)': attempting to reference a deleted function 

这是什么问题?

所以我添加了这个析构函数:

So I added this destructor:

~Foo()
{
    if( type ==3 )
        value.stringValue.~std::wstring();
}

我收到一个错误:

error C2061: syntax error: identifier 'wstring'.

在这种情况下，显然std :: string vs std :: wstring很重要...

Apparently std::string vs std::wstring matter in this case...

对此一无所知.

我现在得到:

 error C2280: 'Foo::<unnamed-type-value>::~<unnamed-type-value>(void)': attempting to reference a deleted function

推荐答案

联合包含一个具有非平凡析构函数的成员( std :: string ).这意味着联合不能拥有默认的析构函数(它不知道要调用哪个成员的析构函数).因此，您需要提供一个自定义析构函数.

The union contains a member (std::string) with a non-trivial destructor. This means that the union can't have a defaulted destructor (it wouldn't know which member's destructor to call). So you need to provide a custom destructor.

在您的情况下，定义一个不执行任何操作的联合析构函数，然后在struct析构函数中进行工作:

In your case define a union destructor that does nothing and then do the work in the struct destructor:

struct Foo {
    int type;

    union U {
        int intValue;
        double doubleValue;
        std::wstring stringValue;

        
        ~U() noexcept {}

    } value;

    ~Foo()
    {
        using std::wstring;

        if (type == 3)
            value.stringValue.~wstring();
    }
};

请注意，复制/移动构造函数/分配也需要这样做.

Please note that you need to do this for copy/move constructor/assignments as well.

在C ++ 17中，您有 std :: variant ，这是一个安全的联合.

In C++17 you have std::variant which is a safe union.

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