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麻烦各位，问个问题

在一个模板类内部说明另一个类是这个类的友元，

如下写法是否正确？

#include<iostream.h> #define MaxVertexes 20 template <class vertexType,class arcType> class Graph;

template <class arcType> class ArcNode{ friend class Graph<class vertexType,class arcType>; private: int adjvex; arcType weight; ArcNode<arcType>*nextarc; public: ArcNode(){} ArcNode(int v,arcType w):adjvex(v),weight(w),nextarc(NULL){} }; template <class vertexType,class arcType> class VertexNode{ friend class Graph <class vertexType,class arcType>; private: vertexType data; ArcNode<arcType>*firstarc; public: VertexNode(){} VertexNode(vertexType v):data(v),firstarc(NULL){} };

我想说明ArcNode和VertexNode为Graph的友元，

friend class Graph<class vertexType,class arcType>;

这句话的下划线的class要不要加，以前都是不加的，编译能通过的，这次老是说有个错误！

如果不加class，两处加下划线和加粗的地方都去掉的话，编译器报如下错误：

Compiling... Graph.cpp F:\tmp\Graph\Graph.cpp(5) : error C2065: 'vertexType' : undeclared identifier F:\tmp\Graph\Graph.cpp(13) : see reference to class template instantiation 'ArcNode<arcType>' being compiled Error executing cl.exe.

Graph.obj - 1 error(s), 0 warning(s)

请问这种格式对吗？class要加吗？

第 2 楼

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#include<iostream>
using namespace std;

int const MaxVertexes = 20;

template  <class vertexType, class arcType>
class ArcNode;
template  <class vertexType,class arcType>
class VertexNode;

template  <class vertexType, class arcType>
class Graph
{
  // your code
};

template  <class vertexType, class arcType>
class ArcNode
{
  friend class Graph <vertexType, arcType>;
private:
  int adjvex;
  arcType weight;
  ArcNode<vertexType, arcType> * nextarc;
public:
  ArcNode(){}
  ArcNode(int v,arcType w):adjvex(v),weight(w),nextarc(NULL){}
};

template  <class vertexType, class arcType>
class VertexNode
{
  friend class Graph <vertexType, arcType>;
private:
  vertexType data;
  ArcNode<vertexType, arcType> * firstarc;
public:
  VertexNode(){}
  VertexNode(vertexType v):data(v),firstarc(NULL){}
};

int main()
{
  // your code ...
  system("pause");
  return 0;
}