Question

what would be a reason for upcasting in C++ in the code which will be used for numerical computations over huge amounts of data (a library that I m using)?

考虑以下等级:

template<class T>
class unallocatedArray
{
    public: 
        unallocatedArray(int size, T t)
            : size_(size), t_(0) 
        {

        }

        // Copy constructor. This is the only way to 
        // actually allocate data: if the array is 
        // passed as an argument to the copy constr.
        // together with the size. 

        // Checks. Access operators. Iterators, etc.  
        // Wrappers for stl sorts...

    private:
        int size_;
        T* t_;
};


template<class T>
class myArray 
: public unallocatedArray<T>
{
    public:
        // This type actually allocates the memory.
        myArray (int size)
            : unallocatedArray<T>(size)
        {
            // Check if size < 0..  

            // Allocate.
            this->t_ = new T[size];
        }

        myArray (int size, T t)
        {
            this->t_ = new T[size];

            for (int i = 0; i < this->size_; i ++ )
            {
                this->t_[i] = t;
            }
        }

        // Some additional stuff such as bound checking and error handling. 
        // Append another array (resizing and memory copies), equality 
        // operators, stream operators, etc...

};

template<class T>
class myField
: public myArray<T>
{
    public: 
        // Constructors call the parent ones. No special attributes added. 

        // Maping operations, arithmetical operators, access operator.
};

//

template<class T>
class geomField
: public myField<T>
{
    // myField but mapped on some kind of geometry, like surface meshes, 
    // volume meshes, etc.  
};

这只是一个非常简化的模式,只是说,准入经营人的定义是一切的,算术操作者被安排在我的外地班。现在,如果需要做1 e07倍以下的话,那么把地平地推向我的外地的理由是什么:

access the element perform arithmetical expression

in the following way:

GeomField<myType> geomFieldObject;

myField<myType>&  downCast = geomFieldObject;

// Do the arithmetical operations on the downCast reference.

两个领域? 是否还预示了某种惩罚? 算术经营者是否没有公开向地球领域提供:这不是公共继承的全部内容?

我没有这样做,而是从一个我正在开发的骨质图书馆中挑选。

感谢!

Answer 1

我只能猜测,但一些测量作业可能已经超出在<代码>geom Field上的文字,以便进行几何制图。

如果您有<代码>geom Field中的数据,但希望开展未规划的行动,这可能是进行预测的原因。

另一方面,如果在投稿后执行的业务中没有一个在<代码>geom Field上手写过。那么,你就不必再 right。

And generally, upcasting doesn t introduce any performance drawbacks because usually (or even in every case, I m not sure right now ...) it is done completely at compilation time: Consider the following classes:

class A {
public:
  void f();
};

class B : public A {
public:
  void f(); // Overwrites A::f
};

当你重新制定法典时

B obj;
obj.f();

汇编者将其翻译成类似内容。

B::f(&obj);

以及

static_cast<A>(obj).f();

成果

A::f(&obj);

i. 不存在通过投放而产生的管理费。

友情链接