c – 未定义的对运算符<<的引用

我有一个普通课(不是一个模板,就是这样),一个私人的朋友运算符<< 它的声明是：

std::ostream& operator<<(std::ostream& out,const Position& position);

在cpp文件中,它的定义是：

std::ostream& operator<<(std::ostream& out,const Position& position)
{
  out << position.getXPoint() << "," << position.getYPoint();
  return out;
}

它正在被编译,然后链接到使用它的主要功能,但是当我使用它,我得到一个未定义的引用…

然而,当我将定义添加到主cpp文件的顶部并删除朋友声明时,它工作正常…

我在我的主要功能中使用它

std::cout << node->getPosition() << std::endl;

不多不少…

遇到链接器错误

并且继承类头

#ifndef PATHFINDER_H
#define PATHFINDER_H
#include <ostream>
#include <istream>
#include <list>
#include <vector>
#include <stdexcept>
#include <cString>
namespace pathfinder
{
class Node;
typedef unsigned int GCost;
typedef std::vector<std::vector<Node*> > World;
typedef std::vector<Node*> WorldRow;
class Position
{
public:
    typedef unsigned int point_type;
private:
    point_type* xPoint_;
    point_type* yPoint_;
    friend std::ostream& operator<<(std::ostream& out,const Position& position);
public:
    Position(const point_type& xPoint = 0,const point_type& yPoint = 0);
    Position(const Position& position);
    Position(Position&& position);
    ~Position();

    Position& operator=(const Position& position);
    Position& operator=(Position&& position);

    point_type getXPoint() const;
    point_type getYPoint() const;

    void setXPoint(const point_type& xPoint);
    void setYPoint(const point_type& yPoint);
};
class Node
{
private:
    bool* isPassable_;
    bool* isStarTingNode_;
    bool* isTargetNode_;
    Position* position_;
    GCost* additionalGCost_;
    Node* parent_;
public:
    Node(const bool& isPassable = true,const bool& isStarTingNode = false,const bool& isTargetNode = false,const Position& position = Position(0,0),const GCost& additionalGCost = 0,Node* parent = nullptr);
    Node(const Node& nodE);
    Node(Node&& nodE);
    ~Node();

    Node& operator=(const Node& nodE);
    Node& operator=(Node&& nodE);

    bool isPassable() const;
    bool isStarTingNode() const;
    bool isTargetNode() const;
    Position getPosition() const;
    GCost getAdditionalGCost() const;
    Node* getParent() const;

    void setAsPassable(const bool& isPassablE);
    void setAsStarTingNode(const bool& isStarTingNodE);
    void setAsTargetNode(const bool& isTargetNodE);
    void setPosition(const Position& position);
    void setAdditionalGCost(const GCost& additionalGCost);
    void setParent(Node* parent);
};
class WorldHelper
{
public:
    static World fromStream(std::istream& input);
    static void syncPositions(World& world);
    static void uninitializeWorld(World& world);
    static Node* findStarTingNode(const World& world);
    static Node* findTargetNode(const World& world);
};
class Pathfinder
{
public:
    virtual std::list<Node*> operator()(World& world) const = 0;
};
};
#endif //PATHFINDER_H

现在删除好友声明后,我收到错误信息,如：

它发生在与std :: cout语句相同的行上…

那么什么交易…

提前致谢

namespace A {
   struct B {
      friend std::ostream& operator<<( std::ostream&,B const & ); // [1]
   };
}
std::ostream& operator<<( std::ostream& o,A::B const & ) {        // [2]
   return o;
}

A::B b;
std::cout << b;

// cpp [assume that the deFinition of B contained a member f
using namespace A;
void B::f() {
}

namespace A {
   struct B  { friend std::ostream& operator<<( std::ostream&,B const & ); };
   std::ostream& operator<<( std::ostream&,B const & );
}
std::ostream& A::operator<<( std::ostream& o,B const & ) {
   return o;
}

namespace A {
   struct B  {
      friend std::ostream& operator<<( std::ostream&,B const & ); // [1]
   };
   std::ostream& operator<<( std::ostream&,B & ) {                // [3]
      return o;
   }
}