您失踪的是指派操作员。 参看rule of three (或 5)。

问题大致如下:

T t; // default constructed t
t = T(2); // T(2) constructor with a single argument, assignment operator= called with this == &t

您不提供派任操作员,因此,临时的点值被简单地复制为拖车,然后在临时代行人中标明的记忆被删除。

Also: Don t have a default constructor, if the object constructed is invalid.

If you object has any user defined constructor it is always constructed using a constructor. Just defining an object without any constructor arguments uses the default constructor independent of whether the object is being overwritten afterwards. That is

FixedByteStream received;

将打电话给违约建筑商。 下面的行文更令人感兴趣:

received = FixedByteStream(12);

This line create a temporary FixedByteStream with the argument 12. Internally this will allocate some memory but since temporaries are destroyed at the end of the full expression (in this case essentially when the semicolon is reached) that won t you do much good. Once this temporary object is constructed it is assigned to received using the automatically generated copy assignment which would look something like this if you d write it manually:

FixedByteStream& FixedByteStream::operator= (FixedByteStream& other) {
    this->existing = other.existing;
    this->size     = other.size;
    this->address  = other.address;
    return *this;
}

That is, once this assignment is executed, you have to identical copies of FixedByteStream, one of which is about to be destroyed and will release the resources just allocated. This is clearly not what you want, i.e. you definitely need to implement the copy assignment operator to make your class well-behaved. In general, the presence of a destructor which does anything interesting is a good hint at the fact that you ll need an assignment operator as well. In fact, there is another one of the generated operations, namely the copy constructor, which does roughly what the copy assignment does except that it copy constructs the members instead of assigning them. This is also not what you want with your class.

现在这个令人感兴趣的问题是:如何使用<代码>。 固定标签。 有效地来说,你要么需要使用参考计数,以跟踪目前有多少物体正在研究<代码>。 固定目录,分配内容的复印件,或需要使用移动自学支持(参考书目),这种支持只在C++2011年提供。 除非你真正知道你正在做些什么,否则我就建议在所有案件中复制这一流,并在以后采用更先进的办法。

一步步:

//create a new object using the default constructor
//I don t see why you think it s stupid that the constructor is called
//it s doing what you re telling it to do
FixedByteStream received;

//FixedByteStream(12) creates a temporary object
//you then copy this object in the received object you already have
//you re using the default operator =
//the temporary object is deleted after it is copied to received
received = FixedByteStream(12);

//received is a valid object
received[0] =  t ;

EDIT:

我看到,对这一问题的答复有很多。 对此,我可能会产生一些仇恨,但这是一个极其重要的概念,我对此表示反对,以便错误的答案不会被接受和放弃。

class A
{
    A() {}
    A(const A& other) {}
    A& operator = (const A& other) {}
};

{ //begin scope
  A a;  //object a is created here
        //default constructor is called
} //a is destroyed here
  //destructor is called

{
   //two objects are created with default constructor
   A a;
   A b;
   //object b is assigned to a
   //operator = will be called
   //both objects are still alive here
   a = b;
   //...
} // a and b will be destroyed, destructor called

{
   A a;
   a = A();
}

{
   A a;
   {
      A b;
      a = b;
   }
}