关于友元函数的问题

weixiaofeng_00 2010-04-24 12:27:28

template <class T>
class Array1D {
public:
Array1D(int sz=0);
~Array1D() { delete [] elements; }
T& operator [] (int i) const; //重载[]，取元素值
Array1D<T>&operator =(const Array1D<T> &r); //整体赋值
friend istream &operator>>(istream &in, Array1D<T> &r);
friend ostream &operator<<(ostream &out, const Array1D<T> &r);
private:
int size;
T *elements; //指向T类型数组的指
};

这是一维数组类的实现。
这个类定义中，friend istream &operator>>(istream &in, Array1D<T> &r);
friend ostream &operator<<(ostream &out, const Array1D<T> &r);有什么错误？为什么用友元函数会出错。
请教高手，谢谢！

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pengzhixi 2010-07-27

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vc6.0对模板和友元支持都相当差劲

weixiaofeng_00 2010-07-27

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不好意思，现在才结贴~虽然我想问的没有完全解决，但还是感谢热心回帖的大虾们~

耍宝王 2010-04-24

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方法一：绑定友元函数模板



template <class T> class Array1D;//类的前向声明

template <class T> istream &operator>>(istream &in, Array1D<T> &r);//函数模板声明

template <class T> ostream &operator<<(ostream &out, const Array1D<T> &r);



template <class T>

class Array1D

{

public:

    Array1D(int sz=0);

    ~Array1D() { delete [] elements; }

    T& operator [] (int i) const; //重载[]，取元素值 

    Array1D<T>&operator =(const Array1D<T> &r); //整体赋值

    friend istream &operator>> <T>(istream &in, Array1D &r);//注意那个<T>，参数中Array1D可以不带<T>

    friend ostream &operator<< <T>(ostream &out, const Array1D &r);

private:

    int size;

    T *elements; //指向T类型数组的指  

};



template <class T>

istream &operator>>(istream &in, Array1D<T> &r)

{

    ...

}



template <class T>

ostream &operator<<(ostream &out, const Array1D<T> &r)

{

    ...

}

方法二：在类内部直接定义

template <class T>

class Array1D

{

public:

    Array1D(int sz=0);

    ~Array1D() { delete [] elements; }

    T& operator [] (int i) const; //重载[]，取元素值 

    Array1D<T>&operator =(const Array1D<T> &r); //整体赋值

    friend istream &operator>>(istream &in, Array1D<T> &r)//此时，默认为内联函数

    {

        ...

    }



    friend ostream &operator<<(ostream &out, const Array1D<T> &r)

    {

        ...

    }

private:

    int size;

    T *elements; //指向T类型数组的指  

};

方法三：类内部直接声明友元函数模板，即，非绑定友元函数模板

template <class T>

class Array1D

{

public:

    Array1D(int sz=0);

    ~Array1D() { delete [] elements; }

    T& operator [] (int i) const; //重载[]，取元素值 

    Array1D<T>&operator =(const Array1D<T> &r); //整体赋值

    template <class Type> friend istream &operator>>(istream &in, Array1D<Type> &r);

    template <class Type> friend ostream &operator<<(ostream &out, const Array1D<Type> &r);

private:

    int size;

    T *elements; //指向T类型数组的指  

};

template <class Type>

istream &operator>>(istream &in, Array1D<Type> &r)

{

    ...

}



template <class Type>

ostream &operator<<(ostream &out, const Array1D<Type> &r)

{

    ...

}

方法四：LZ你的方法

template <class T>

class Array1D

{

public:

    Array1D(int sz=0);

    ~Array1D() { delete [] elements; }

    T& operator [] (int i) const; //重载[]，取元素值 

    Array1D<T>&operator =(const Array1D<T> &r); //整体赋值

    friend istream &operator>>(istream &in, Array1D<T> &r);

    friend ostream &operator<<(ostream &out, const Array1D<T> &r);

private:

    int size;

    T *elements; //指向T类型数组的指  

};



//根据实例直接定义函数实体，比如使用Array1D<int>的对象

//这是普通函数，应此不需要template <class T>

istream &operator>>(istream &in, Array1D<int> &r)//如要用Array1D<char>的对象需要另行定义一个函数

{

    ...

}

ostream &operator<<(ostream &out, const Array1D<int> &r)

{

    ...

}

LZ请参考http://blog.csdn.net/peimichael/archive/2009/11/28/4894000.aspx

aweer 2010-04-24

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template<class T>

friend ostream& operator<<(ostream&,const Array1D<T> &r);

template<class T>

friend istream &operator>>(istream &in, Array1D<T> &r);

template <class T>

class Array1D {

  public:

  Array1D(int sz=0);

  ~Array1D() { delete [] elements; }

  T& operator [] (int i) const; //重载[]，取元素值  

  Array1D<T>&operator =(const Array1D<T> &r); //整体赋值

  friend istream &operator>> <T>(istream &in, Array1D<T> &r);

  friend ostream &operator<< <T>(ostream &out, const Array1D<T> &r);

  private:

  int size;

  T *elements; //指向T类型数组的指   

};