c++ - 获取 "Use of undefined type"和 "Must have class/struct/union"错误

Question

编辑 #1:编辑行之前的所有内容

<< "Owner: " << (*wo._owner).getLoginName() << endl;

工作得很好，或者至少没有向我抛出错误。

所以我有以下代码(显然还有很多，如果需要我会发布，只是不确定是否需要更多或者没问题):

class Workout
{
private:
    int _workoutid; // the ID of this workout
    User* _owner; // Who did this workout
    float _distance; // in miles
    int _duration; // in seconds
    int _day, _month, _year; // date: MM/DD/YYYY
    int _weight; // lb, on the date of workout
    // private methods (if necessary)
public:
    friend std::ostream& operator<< (ostream& out, Workout& wo)
    {
        out << "Workout ID: " << wo._workoutid << endl
            << "Owner: " << (*wo._owner).getLoginName() << endl
            << "Distance: " << wo._distance << endl
            << "Duration: " << wo._duration / 3600 << ":" << (wo._duration % 3600) / 60 << ":" << wo._duration % 60 << endl
            << "Date: " << wo._month << ":" << wo._day << ":" << wo._year << endl
            << "Weight: " << wo._weight << endl;
        return out;
    }
    // Print workout id, owner’s username, distance
    // duration (HH:MM:SS), date (MM:DD:YY) and weight of
    // the workout
    // and other public methods (mutators/setters, accessors/getters)
    Workout(void);
    Workout(int, User*, float, int, int, int, int, int);
    virtual ~Workout(void);
    float getDistance();
    void setDistance(float);
};
Workout::Workout(void) : _workoutid(), _distance(), _duration(), _day(), _month(), _year(), _weight()
{
    _owner = new User();
}
Workout::Workout(int id, User* user, float distance, int duration, int day, int month, int year, int weight) :
_workoutid(id), _distance(distance), _duration(duration), _day(day), _month(month), _year(year), _weight (weight), _owner(user)
{
}
Workout::~Workout(void)
{
    delete [] _owner;
}

class User
{
private:
    char* _firstname; // First name
    char* _lastname; // Last name
    char* _loginname; // Login name
    char* _password; // password
    Workout* _myWorkouts[50];// an array of pointers to workouts
    int _numWorkouts; // Num. of workout logged
    User* _buddies[10]; // Friends
    int _numBuddies; // Num. of friends

    // private methods (if necessary)

public:
    friend std::ostream& operator<< (ostream& out, User& user)
    {
        out << "First Name: [" << user._firstname << "]" << endl
            << "Last Name: ["<< user._lastname << "]" << endl
            << "Login Name: [" << user._loginname << "]" << endl
            << "Number of Workouts: [" << user._numWorkouts << "]" << endl
            << "Number of Friends: [" << user._numBuddies << "]" << endl;
        return out;
    }
    User(void);
    User(const char*, const char*, const char*, const char*);
    virtual ~User(void);

    char* getPassword(void);
    char* getLoginName(void);
    char* getFirstName(void);
    void addWorkout(Workout*);
    Workout* getWorkout(int);
    void addBuddy(User* buddy);
    // and other public methods (mutators/setters, accessors/getters)
};
User::User(void) : _firstname(), _lastname(), _loginname(), _password(),
    _myWorkouts(), _numWorkouts(), _buddies(), _numBuddies()
{
}
User::User(const char* first, const char* last, const char* login, const char* pass) : _myWorkouts(), _numWorkouts(), _buddies(), _numBuddies()
{
    _firstname = new char[20];
    _lastname = new char[20];
    _loginname = new char[20];
    _password = new char[20];

    for (int i=0; i < 20; i++){
        _firstname[i] = first[i];
        _lastname[i] = last[i];
        _loginname[i] = login[i];
        _password[i] = pass[i];
    }
}
User::~User(void)
{
    delete [] _firstname;
    delete [] _lastname;
    delete [] _loginname;
    delete [] _password;

    for(int i=0;i<50;i++) delete _myWorkouts[i];
    delete [] _myWorkouts;

    for(int i=0;i<10;i++) delete _buddies[i];
    delete [] _buddies;

    //What about variables such as _numWorkouts and _numBuddies?
}

我收到以下错误:

Error 1 error C2027: use of undefined type 'User'

Error 2 error C2228: left of '.getLoginName' must have class/struct/union

第一个错误是因为 operator<< 方法不知何故不想识别 User 类型的 (*wo._owner) 对象已初始化(它是!)第二个错误，显然必须与第二个错误有关，但它根本没有提高我意识到如何解决问题的机会。

Answer 1

如果这确实是您代码的结构，那么您正在尝试在定义它之前使用“User”。

你不能这样做。

如果需要，将您的输出运算符声明为友元，并在知道 User 的定义后定义它。