C++ 在类（C+；+；）中使用模板时未声明成员函数

我在代码中使用了以下类

class pos2d
{
    float x, y;
public:
    float getx() const;
    float gety() const;
    //int getz() const;                    //How to avoid??
};

class pos3d
{
    float x, y, z;
public:
    float getx() const;
    float gety() const;
    float getz() const;
};

template<class T, class P>
class entity
{
    T type;
    P position;
public:
    void print() const;
};

类pos2d
{
浮动x，y；
公众：
float getx（）常量；
float gety（）常量；
//int getz（）const；//如何避免？？
};
类pos3d
{
浮动x，y，z；
公众：
float getx（）常量；
float gety（）常量；
float getz（）常量；
};
模板
类实体
{
T型；
P位；
公众：
无效打印（）常量；
};

我在类实体中的打印函数如下

template<class T, class P>
void entity<T, P>::print() const
{
    if (type == 1 || type == 'A')
        cout << "Object is of type " << type << " and has coordinates as (" << position.getx() << ", " << position.gety() << ", " << position.getz() << ")\n\n"; //Avoid getz in pos2d
    else if (type == 2 || type == 'B')
        cout << "Object is of type " << type << " and has coordinates as (" << position.getx() << ", " << position.gety() << ")\n\n";
}

模板
void实体：：print（）常量
{
如果（类型==1 | |类型==A）
我可以看到两种简单的方法来实现这一点：

-使print（）成为posX类的成员函数。
-在实体类中专门化print（）函数。
    #include <iostream>

    class pos2d
    {
        float x, y;
    public:
        float getx() const { return x; }
        float gety() const { return y; }
        void print() const
        {
            std::cout << "Object is of type and has coordinates as (" << getx() << ", " << gety() << ")\n\n";
        }
    };

    class pos3d
    {
        float x, y, z;
    public:
        float getx() const { return x; }
        float gety() const { return y; }
        float getz() const { return z; }
        void print() const
        {
            std::cout << "Object is of type  and has coordinates as (" << getx() << ", " << gety() << ", " << getz() << ")\n\n";
        }
    };

    template <class P>
    class entity
    {
        P position;
    public:
        void print() const { position.print(); }
        void print_specialized() const;
    };

    template <>
    void entity<pos3d>::print_specialized() const {
        std::cout << "Object is of type  and has coordinates as (" << position.getx() << ", " << position.gety() << ", " << position.getz() << ")\n\n";
    }

    template <>
    void entity<pos2d>::print_specialized() const  {
        std::cout << "Object is of type and has coordinates as (" << position.getx() << ", " << position.gety() << ")\n\n";
    }


    int main() {
        entity<pos2d> e;
        e.print();
        e.print_specialized();
        entity<pos3d> e2;
        e2.print();
        e2.print_specialized();
        return 0;
    }

#包括
类pos2d
{
浮动x，y；
公众：
float getx（）常量{return x；}
float gety（）常量{return y；}
void print（）常量
{
std:：cout问题在于，如果将
pos2d
作为模板参数传递给行

cout << "Object is of type " << type << " and has coordinates as (" << position.getx() << ", " << position.gety() << ", " << position.getz() << ")\n\n";

检索2D向量（或点）的<代码> z < /代码>坐标是没有意义的。考虑使用sFIAE。查看关于<代码> STD:：Enable的文档，如果
template<class P>
class entity
{
    P position;
public:
    void print() const;
};

template<>
void entity<pos3d>::print() const
{
    cout << "Object is of type pos3d and has coordinates as (" 
         << position.getx() << ", " << position.gety() << ", " << position.getz() << ")\n\n";
}        

template<>
void entity<pos2d>::print() const
{
        cout << "Object is of type pos2d and has coordinates as (" 
             << position.getx() << ", " << position.gety() << ")\n\n";
}