一个关于模板的问题

[fanhj_2007]

/*
* intArray.h
*
* Created on: 2009-4-7
* Author: Administrator
*/

#ifndef INTARRAY_H_
#define INTARRAY_H_
#include <iostream>
using namespace std;
template <class T>
class Array {
public:
T& operator[ ] (int );
const T& operator[ ](int ) const;
Array (int );
~Array();
int get_size() const;
private:
T* a;
int size;
Array(); //for emphasis(重点)
T dummy_val; // rerurned on bad index
};
template <class T>
T& Array<T>::operator[ ](int i) {
if ( i < 0 || i >= size ) {
cerr << "index "<< i << "out of bounds";
return dummy_val;
}
return a[i];
}

template <class T>
const T& Array<T>::operator[ ](int i) const {
if ( i < 0 || i >= size ) {
cerr << "index "<< i << "out of bounds";
return dummy_val;
}
return a[i];
}

template <class T>
Array < T > :: Array( int s) {
a = new T[size = s];
}

template <class T>
Array< T > :: ~Array() {
delete[ ] a;
}
// top-level overload of operator <<
template <class T>
ostream& operator<< (ostream& os, const Array< T>& ar) {
for (int i = 0; i < ar.get_size(); i++)
os << ar[i] <<endl;
return os;
}


#endif /* INTARRAY_H_ */




#include <iostream>
#include "Array.h"
using namespace std;
int main() {
Array<int> a(3);
a[0] = 0;
a[1] = 1;
a[2] = 2;
cout << a;
return 0;
}
代码我完全是按照书本上抄写的，我的eclipse编译完后说有一个错误，但是那个红色的小X只是在工程文件上有，而具体的代码上没，
error 提示：make****（array.exe）error 1

[「已注销」]

添加get_size方法：

template <class T>
int Array < T > :: get_size() const {
    return size;
}

[「已注销」]

下面完整代码编译通过，输出0,1,2

#include <iostream>

using namespace std;
template <class T>
class Array {
public:
    T& operator[ ](int);
    const T& operator[ ](int) const;
    Array(int);
    ~Array();
    int get_size() const;
private:
    T* a;
    int size;
    Array();  //for emphasis(重点)
    T dummy_val; // rerurned on bad index
};
template <class T>
T& Array <T>::operator[ ](int i) {
    if (i < 0 || i >= size) {
        cerr << "index " << i << "out of bounds";
        return dummy_val;
    }
    return a[i];
}

template <class T>
const T& Array <T>::operator[ ](int i) const {
    if (i < 0 || i >= size) {
        cerr << "index " << i << "out of bounds";
        return dummy_val;
    }
    return a[i];
}

template <class T>
Array < T > :: Array(int s) {
    a = new T[size = s];
}

template <class T>
Array < T > :: ~Array() {
    delete[ ] a;
}

template <class T>
int Array < T > :: get_size() const {
    return size;
}

// top-level overload of operator <<
template <class T>
ostream& operator << (ostream& os, const Array < T>& ar) {
    for (int i = 0; i < ar.get_size(); i++)
        os << ar[i] << endl;
    return os;
}



using namespace std;
int main() {
    Array <int> a(3);
    a[0] = 0;
    a[1] = 1;
    a[2] = 2;
    cout << a;
    return 0;
}

[猫已经找不回了]

int get_size() const;

有声明就得实现它，哪怕实现操作为空也行。