Header:

#ifndef _DAYTIME_
#define _DAYTIME_
#include <iostream> 
using namespace std;

class DayTime
{
      private:
              short hour, minute, second;
              bool overflow;
      public:
             DayTime( int h = 0, int m = 0, int s = 0 );
             bool setTime(int hour, int minute, int second = 0);
             int getHour() const {return hour;}
             int getMinute() const {return minute;}
             int getSecond() const {return second;}

             int asSeconds() const //Tageszeit als Sekunden
             {
                 return (60*60*hour + 60*minute + second);
             }
             bool operator<( const DayTime& t) const
             {                                 // *this mit t vergl.
                  return asSeconds() < t.asSeconds();
             }
             DayTime& operator++()                   // Sekunden erhöhen
             {
                      ++second;
                      return *this;
             }
             void print () const;

      };
#endif //_DAYTIME_

CPP Datei:

#include "DayTime.h"

int main()
{
DayTime abflug1(11,11,11), abflug2(12,0,0);
if(abflug1 < abflug2)
cout << "1. früher" << endl;
cin.get();
}

Fehler:

[Linker error] undefined reference to `DayTime::DayTime(int, int, int)'

Grüssli