类外的默认构造函数/析构函数？ [英] Default constructor/destructor outside the class?

问题描述

根据C ++ 11标准（ =默认在类的定义之外），以下内容是合法的吗？

  //在头文件中
 class Test 
 {
 public：
 Test（）; 
〜Test（）; 
}; 
 
 //在cpp文件中
 Test :: Test（）= default; 
 Test ::〜Test（）= default;是的，一个特殊的成员函数可以是默认定义的，它可以是一个特定的成员函数，它可以是一个特定的成员函数。 out-of-line在.cpp文件中。意识到，通过这样做，内联默认函数的一些属性将不适用于您的类。例如，如果你的拷贝构造函数是默认定义的，那么你的类不会被认为是可以复制的（它也不能被识别为POD）。类似地，默认定义的out-of-line析构函数将取消你的类型是不重要的（或POD）。
 
 
 
 - 内联复制构造函数和控制它在哪里定义（可能控制生成的模板定义它将需要），但不希望手动定义一个手工成员初始化列表，这将是费力的并可能在维护下过时。
 
Is the following legal according to the C++11 standard (= default outside the definition of the class) ?
// In header file
class Test
{
    public:
        Test();
        ~Test();
};

// In cpp file
Test::Test() = default;
Test::~Test() = default;

解决方案
Yes, a special member function can be default-defined out-of-line in a .cpp file.  Realize that by doing so, some of the properties of an inline-defaulted function will not apply to your class.  For example, if your copy constructor is default-defined out-of-line, your class will not be considered trivially copyable (which also disqualifies it from being recognized as a POD).  Similarly, a default-defined out-of-line destructor will disqualify your type from being trivial (or POD).

This can be useful if you wish to have a non-inline copy-constructor and control over where it is defined (perhaps to take control over generated template definitions it will require), but don't wish to manually define it yourself with a hand-crafted member-initializer list, which would be laborious and could go stale under maintenance.

                        
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