2014.10.9 模板函数做友元函数的问题

1.模板函数作为类的友元函数，要先声名。

2.在类的定义中声明友元时要在函数后加上<T>

  1 #ifndef Array1D_
  2 #define Array1D_
  3
  4 // One-dimensional arrays.
  5
  6 #include <iostream>
  7 #include "xcept.h"
  8
  9
 10 template <class T> class Array1D;
 11 //template <class T> std::istream &operator>>(std::istream &in, Array1D<T> &r);//函数模板做友元要先声明
 12 template <class T> std::ostream& operator<<(std::ostream&, const Array1D<T>&);
 13
 14 template<class T>
 15 class Array1D {
 16    friend std::ostream& operator<<<T>
 17           (std::ostream&, const Array1D<T>&);
 18    public:
 19       Array1D(int size = 0);
 20       Array1D(const Array1D<T>& v); // copy constructor
 21       ~Array1D() {delete [] element;}
 22       T& operator[](int i) const;
 23       int Size() {return size;}
 24       Array1D<T>& operator=(const Array1D<T>& v);
 25       Array1D<T> operator+() const; // unary +
 26       Array1D<T> operator+(const Array1D<T>& v) const;
 27       Array1D<T> operator-() const; // unary minus
 28       Array1D<T> operator-(const Array1D<T>& v) const;
 29       Array1D<T> operator*(const Array1D<T>& v) const;
 30       Array1D<T>& operator+=(const T& x);
 31       Array1D<T>& ReSize(int sz);
 32    private:
 33        int size;
 34        T *element; // 1D array
 35 };
 36
 37 template<class T>
 38 Array1D<T>::Array1D(int sz)
 39 {// Constructor for one-dimensional arrays.
 40    if (sz < 0) throw BadInitializers();
 41    size = sz;
 42    element = new T[sz];
 43 }
 44
 45 template<class T>
 46 Array1D<T>::Array1D(const Array1D<T>& v)
 47 {// Copy constructor for one-dimensional arrays.
 48    size = v.size;
 49    element = new T[size];  // get space
 50    for (int i = 0; i < size; i++) // copy elements
 51       element[i] = v.element[i];
 52 }
 53
 54 template<class T>
 55 T& Array1D<T>::operator[](int i) const
 56 {// Return reference to element i.
 57    if (i < 0 || i >= size) throw OutOfBounds();
 58    return element[i];
 59 }
 60
 61 template<class T>
 62 Array1D<T>& Array1D<T>::operator=(const Array1D<T>& v)
 63 {// Overload assignment operator.
 64    if (this != &v) {// not self-assignment
 65       size = v.size;
 66       delete [] element; // free old space
 67       element = new T[size]; // get right amount
 68       for (int i = 0; i < size; i++) // copy elements
 69          element[i] = v.element[i];
 70       }
 71    return *this;
 72 }
 73
 74 template<class T>
 75 Array1D<T> Array1D<T>::
 76            operator+(const Array1D<T>& v) const
 77 {// Return w = (*this) + v.
 78    if (size != v.size) throw SizeMismatch();
 79
 80    // create result array w
 81    Array1D<T> w(size);
 82    for (int i = 0; i < size; i++)
 83        w.element[i] = element[i] + v.element[i];
 84
 85    return w;
 86 }
 87
 88 template<class T>
 89 Array1D<T> Array1D<T>::
 90            operator-(const Array1D<T>& v) const
 91 {// Return w = (*this) - v.
 92    if (size != v.size) throw SizeMismatch();
 93
 94    // create result array w
 95    Array1D<T> w(size);
 96    for (int i = 0; i < size; i++)
 97        w.element[i] = element[i] - v.element[i];
 98
 99    return w;
100 }
101
102 template<class T>
103 Array1D<T> Array1D<T>::operator-() const
104 {// Return w = -(*this).
105    // create result array w
106    Array1D<T> w(size);
107    for (int i = 0; i < size; i++)
108        w.element[i] = -element[i];
109
110    return w;
111 }
112
113 template<class T>
114 Array1D<T> Array1D<T>::operator*(const Array1D<T>& v) const
115 {// Return w = (*this) * v. Pairwise multiply.
116    if (size != v.size) throw SizeMismatch();
117
118    // create result array w
119    Array1D<T> w(size);
120    for (int i = 0; i < size; i++)
121        w.element[i] = element[i] * v.element[i];
122
123    return w;
124 }
125
126 template<class T>
127 Array1D<T>& Array1D<T>::operator+=(const T& x)
128 {// Add x to each element of (*this).
129    for (int i = 0; i < size; i++)
130        element[i] += x;
131    return *this;
132    }
133
134 template<class T>
135 std::ostream& operator<<(std::ostream& out,
136                     const Array1D<T>& x)
137 {// Put the elements of x into the stream out.
138    for (int i = 0; i < x.size; i++)
139       out << x.element[i] << "  ";
140    return out;
141 }
142
143 template<class T>
144 Array1D<T>& Array1D<T>::ReSize(int sz)
145 {// Change the size to sz.
146  // Do not copy array elements to new space.
147    if (sz < 0) throw BadInitializers();
148    delete [] element;
149    size = sz;
150    element = new T [size];
151    return *this;
152 }
153
154 #endif

以上为本次实验的实例代码，由于没有先进行声明，编译可以通过，执行时会报错

code block：对‘operator<<(std::ostream&, Array1D<int> const&)’未定义的引用VS：error LNK2019: 无法解析的外部符号