C++ 不明确的运算符重载错误

Question

我终于让我的作业几乎完成了，但是现在我在编译它时遇到了一组全新的错误。

#include <iostream>

using namespace std;

class clockType
{
      friend ostream& operator<<(ostream&, const clockType&);
      friend istream& operator>>(istream&, clockType&);
public:
      void setTime (int hours, int minutes, int seconds);
      void getTime (int& hours, int& minutes, int& seconds) const;     
      clockType operator++();
      bool operator==(const clockType& otherClock) const;
      bool operator!= (const clockType& otherClock) const;
      bool operator<=(const clockType& otherClock) const;
      bool operator<(const clockType& otherClock) const;
      bool operator>=(const clockType& otherClock) const;
      bool operator>(const clockType& otherClock) const;
      clockType ();
      clockType (int hours = 0, int minutes = 0, int seconds = 0);
private:
        int hr;
        int min;
        int sec;
};
clockType clockType::operator++()
{
          sec++;
          if (sec > 59)
          {
              sec = 0;
              min++;
              if (min > 59)
              {
                      min = 0;
                      hr++;
                      if (hr > 23)
                      hr = 0;
              }
          }
          return *this;
}
bool clockType::operator==(const clockType& otherClock) const
{
     return (hr == otherClock.hr && min == otherClock.min && sec == otherClock.sec);
}
bool clockType::operator<=(const clockType& otherClock) const
{
     return ((hr < otherClock.hr) || (hr == otherClock.hr && min < otherClock.min) || (hr == otherClock.hr && min == otherClock.min && sec <= otherClock.sec));
}
bool clockType::operator!=(const clockType& otherClock) const
{
          return (hr != otherClock.hr || min != otherClock.min || sec != otherClock.sec);
}
bool clockType::operator<(const clockType& otherClock) const
{
     return ((hr < otherClock.hr) || (hr == otherClock.hr && min < otherClock.min) || (hr == otherClock.hr && min == otherClock.min && sec < otherClock.sec));
}
bool clockType::operator>=(const clockType& otherClock) const
{
     return ((hr > otherClock.hr) || (hr == otherClock.hr && min > otherClock.min) || (hr == otherClock.hr && min == otherClock.min && sec >= otherClock.sec));
}
bool clockType::operator>(const clockType& otherClock) const
{
     return ((hr > otherClock.hr) || (hr == otherClock.hr && min > otherClock.min) || (hr == otherClock.hr && min == otherClock.min && sec > otherClock.sec));
}

void clockType::setTime(int hours, int minutes, int seconds)
{
     if (0 <= hours && hours < 24)
     hr = hours;
     else
     hr = 0;
     if (0 <= minutes && minutes < 60)
     min = minutes;
     else
     min = 0;
     if (0 <= seconds && seconds < 60)
     sec = seconds;
     else
     sec = 0;
}
void clockType::getTime(int& hours, int& minutes, int& seconds)const
{
     hours = hr;
     minutes = min;
     seconds = sec;
}
clockType::clockType(int hours, int minutes, int seconds)
{
 setTime(hours, minutes, seconds);
}
ostream& operator<<(ostream& osObject, const clockType& timeOut)
{
         if (timeOut.hr < 10)
         osObject << '0';
         osObject << timeOut.hr << ':';
         if (timeOut.min < 10)
         osObject << '0';
         osObject << timeOut.min << ':';
         if (timeOut.sec < 10)
         osObject << '0';
         osObject << timeOut.sec << ':';
         return osObject;
}
istream& operator>>(istream& is, clockType& timeIn)
{
         char ch;
         is >> timeIn.hr;
         if (timeIn.hr < 0 || timeIn.hr >=24)
         timeIn.hr = 0;
         is.get(ch);
         is >> timeIn.min;
         if (timeIn.min < 0 || timeIn.min >= 60)
         timeIn.min = 0;
         is.get(ch);
         is >> timeIn.sec;
         if (timeIn.sec < 0 || timeIn.sec >= 60)
         timeIn.sec = 0;
         return is;
}
int main() 
{ 
   clockType  myClock(4, 9, 22);
   clockType yourClock ();

   cout << "myClock = " << myClock << endl;
   cout << "yourClock = " << yourClock << endl;
   cout << "enter the time in form " << "hr:min:sec ";
   cin >> myClock;
   cout << endl;
   cout << "The new time of myClock = " << myClock << endl; 
   ++myClock;
   cout << "After incrementing the time, " << "myClock = " << myClock << endl;
   yourClock.setTime(15, 20, 25);
   cout << "After setting the time, " << "yourClock = " << yourClock << endl;
   if (myClock == yourClock)
   cout << "The times of myClock and " << "yourClock are equal." << yourClock << endl;
   else
   cout << "The times of myClock and " << "yourClock are not equal." << endl;
   if (myClock <= yourClock)
   cout << "The time of myClock is " << "less than or equal to " << endl << "the time of yourClock " << endl;
   else
   cout << "The time of myClock is " << "greater than the time of " << "yourClock." << endl;
   return 0;
}

我得到的错误是:

In funct main();
call of overloaded 'clockType()' is ambiguous candidates are: clockType::clockTYpe(int, int, int) clockType::clockType().

我不确定这是在问我什么，或者真正的错误是什么。

Answer 1

如果没有参数，你的两个构造函数都是候选对象。

clockType();                                                 // takes zero parameters.
clockType (int hours = 0, int minutes = 0, int seconds = 0); // can take zero parameters.

// Thus the compiler does not know whaich one to call.

这也不是你所期望的:

clockType yourClock();

这是一个采用零参数并返回 clockType 对象的函数的前向声明。你真正的意思是:

clockType yourClock;

// or
clockType yourClock = clockType();

这称为 "Most Vexing Parse"问题。