使用了未定义的类_解决方法

在游戏类的编写中，遇到了一个导入工程后运行出现”使用了未定义的类“的错误。

绞尽脑汁也没搞懂是哪里出现了问题，看了其他人的blog后才发现了问题所在：类定义的顺序

第一次错误代码如下：

class Hp : public res{private:int hpValue;//the value of hp this kind of medicine can provide;int number;//the number of the kind of medicine that people has;public:Hp(){}void setHpValue(int value){hpValue = value;}Hp(int value, string _name){    type = 1;//define the type is hp;hpValue = value;//define the value of hp provided;name = _name;//define the name of the medicine;number = 0;//define the number of the medicine(initialized);}int getType(){return type;//get the type of the medicine;}void used(Person &person){

person.addHp();

}void sub(int _number){number -= _number;      //subcline number medicines;}void add(int _number){number += _number;      //add the number medicines;}int getNumber(){return number;        //return the number of the medicine;}void setNumber(int value){number = value;//set the number of the medicine;}};

class Person{a function with Hp parament;};

有代码可以看出来，在hp类中使用到了person类，而在person类中也使用到了hp类，所以出现的定义问题。但是要怎么解决呢？

第一次修改，知道了类定义可以先声明的说法后，在第一排添加了 class Person；

可是，还是失败，于是乎，看见了某大佬的blog，发现原来在类中只要涉及到还没有实现的类的函数，也要先声明，然后在类的最后实现，于是，最后改为

class Person;class Hp : public res{private:int hpValue;//the value of hp this kind of medicine can provide;int number;//the number of the kind of medicine that people has;public:Hp(){}void setHpValue(int value){hpValue = value;}Hp(int value, string _name){    type = 1;//define the type is hp;hpValue = value;//define the value of hp provided;name = _name;//define the name of the medicine;number = 0;//define the number of the medicine(initialized);}int getType(){return type;//get the type of the medicine;}void used(Person &person);void sub(int _number){number -= _number;      //subcline number medicines;}void add(int _number){number += _number;      //add the number medicines;}int getNumber(){return number;        //return the number of the medicine;}void setNumber(int value){number = value;//set the number of the medicine;}};class Person{};void Hp::used(Person &person){person.addHp(hpValue);  //add the hp of the person;sub(1);//the number of the medicine subcline 1;}

于是乎，成功了！