c++ - 在 C++ 中声明模板

Question

// stdafx.h 

// stdafx.h : include file for standard system include files,
// or project specific include files that are used frequently, but
// are changed infrequently
//


#include "targetver.h"
#include <stdio.h>
#include <tchar.h>
#include <iostream>
using namespace std;
#include "Animal.h"

// TODO: reference additional headers your program requires here

class Animal
{
private:
    int itsWeight;
public:
    Animal(int);
    Animal();
    ~Animal() {}
    int getWeight() const { return itsWeight; }
    void Display() const;
};


template <class T>
class Array
{
private:
    T *pType;
    int itsSize;
    const int defaultSize = 10;
public:

    //constructors
    Array(int itsSize = defaultSize);
    Array(const Array &rhs);
    ~Array() { delete[] pType; }

    //operators
    Array& operator=(const Array&);
    T& operator[](int offSet){ return pType[offSet]; }
    const T& operator[](int offSet) const { return pType[offSet]; }

    //methods of Access
    int getSize() const { return itsSize; }
};

//constructor
template <class T>
Array<T>::Array(int size) :
itsSize(size)
{
    pType = new T[size];
    for (int i = 0; i < size; i++)
    {
        pType[i] = 0;
    }
}

//copy-constructor
template <class T>
Array<T>::Array(const Array &rhs)
{
    itsSize = rhs.getSize();
    pType = new T[itsSize];
    for (int i = 0; i < itsSize; i++)
    {
        pType[i] = rhs[i];
    }
}

//operator prisvoeniya
template <class T>
Array<T>& Array<T>::operator=(const Array &rhs)
{
    if (this == &rhs)
      return *this;
    delete[] pType;
    itsSize = rhs.getSize();
    pType = new T[itsSize];
    for (int i = 0; i < itsSize; i++)
    {
        pType[i] = rhs[i];
    }
    return *this;
}

//this is the file "Animal.cpp"

#include "stdafx.h"
#include "Animal.h"

Animal::Animal()
{
    itsWeight = 0;
}

Animal::Animal(int weight)
{
    itsWeight = weight;
}

void Animal::Display() const
{
    cout << itsWeight;
}
// the main function

#include "stdafx.h"

int_tmain(int argc, _TCHAR* argv[])
{

Array<int> theArray;    //Integer array
Array<Animal> theZoo;   //Animal array
Animal *pAnimal;

//filling the array
    for (int i = 0; i < theArray.getSize(); i++)
    {
        theArray[i] = i * 2;
        pAnimal = new Animal[i * 3];
        theZoo[i] = *pAnimal;
        delete pAnimal;
    }

    for (int j = 0; j < theArray.getSize(); j++)
    {
        cout << "theArray[" << j << "]:\t";
        cout << theArray[j]<<"\t\t";
        cout << "theZoo[" << j << "]:\t";
        theZoo[j].Display();
        cout << endl;
    }

    return 0;
}

问题是:编译器给我错误

Error 1 error C2648: 'Array<int>::defaultSize' : use of member as default parameter requires static member
d:\documents\work\c++ files\tigrans\homework10\templates\templates\templates\animal.h 28 1 Templates

Error 2 error C2648: 'Array<Animal>::defaultSize' : use of member as default parameter requires static member
d:\documents\work\c++ files\tigrans\homework10\templates\templates\templates\animal.h 28 1 Templates

任何人都可以帮助我理解这一点。我改变了

const int defaultSize=10;

到

static const int defaultSize=10 

然后没有错误，但在那个时候显示Debug Assertion Failed!

Answer 1

你的这部分代码很狡猾

{
    pAnimal = new Animal[i * 3];
    theZoo[i] = *pAnimal;
    delete pAnimal;
}

第一行分配一个 i*3 Animal 数组，使用它们的默认构造函数(它使 Animal 和 它的权重=0)。在第二行中，您将这些新分配的第一个 Animal 分配给 theZoo[i]。最后，第三行尝试取消分配 Animal。

最后一行包含错误，因为您对通过 new [] 获得的指针调用了 delete。

在堆上创建对象只是为了立即销毁它们的整个概念是相当可疑的——也许你来自另一种编程语言，这是创建对象的唯一方法？首先，您可以简单地使用一个自动变量

{
    Animal a;   // or a(i*3);
    theZoo[i] = a;
}

或者更简短

{
    theZoo[i] = Animal(i*3);
}

(请注意，如果您要使用 std 容器，您可以说 theZoo.emplace_back(i*3);，避免复制 Animal.)