使用友员出现警告的问题?

[HNLGDXYJS]

我的代码如下,因为我是想实现图的各种操作,原代码很长,所以只贴了一部分,友元函数已经定义.且没错.
但是编译器会出警告.大家看下是怎么回事?谢谢.

#include<iostream>
using namespace std;

template<typename T,typename E>
class MatrixGraph
{
    T *VerticesList;     //vertex table
    E **Edge;           //Adjacent matrix
    friend istream& operator >>(istream& in,MatrixGraph<T,E>& G);
    friend ostream& operator <<(ostream& out,MatrixGraph<T,E>& G);
public:
    MatrixGraph(int sz=defaultVertices);
    ~MatrixGraph()
    {
        delete [] VerticesList;
        delete [] Edge;
    }
};


template<typename T,typename E>
MatrixGraph<T,E>::MatrixGraph(int sz)
{
    maxVertices = sz;
    numVertices = numEdges = 0;
    VerticesList = new T[maxVertices];    //create array of vertex table
    Edge =  new int *[maxVertices];  //create array of AdjacentMatrix
    for (int i=0;i<maxVertices;i++)
          Edge[i] = new int[maxVertices];
    for (int i=0;i<maxVertices;i++)
          for (int j=0;j<maxVertices;j++)
            Edge[i][j] = (i==j) ? 0 : maxWeight;
}

int main(void)
{
    //MatrixGraph<int,int> AdjMatG(10);
    return 0;
}

警告信息如下 :

[Warning] friend declaration `std::istream& operator>>(std::istream&, MatrixGraph<T, E>&)'
declares a non-template function

[lzr4304061988012]

http://topic.csdn.net/u/20081115/20/8dd78af6-4a6f-4de9-bff1-94add5b618f9.html

[Non_Recursive]

提前声明模板函数,或者在类中定义友元试一下..

[帅得不敢出门]

up下.

[HNLGDXYJS]

谢谢两位,已解决.