Problém s kopírovacím konstruktorem v kompilátoru Dev c++ 4.9.9.2 – C / C++ – Fórum – Programujte.com

Zdravím, mám problémy s kopírovacím konstructorem, který se nevolá, když požiju kteroukoliv funkci v třídě. Mám přečtenou knihu Naučte se C++ za 21 dní (2007).Zde je příklad:

 

#include <iostream>

using namespace std;

class Division
{
      public:
            Division ();
            Division (Division&);
            ~Division ();
            float GetDownValue () const {return itsDownValue;}
            float GetResultValue () const {return itsResultValue;}
            float GetUpValue () const {return itsUpValue;}
            void SetDownValue (float downValue) {itsDownValue = downValue;}
            void SetUpValue (float upValue) {itsUpValue = upValue;}
            class xNullDownValue {};
      private:
              float itsDownValue;
              float itsResultValue;
              float itsUpValue;
};

Division::Division ():
                      itsDownValue(1),
                      itsResultValue(0),
                      itsUpValue(0)
                      {
                                   cout << "Constructor" << endl;
                      }

Division::Division (Division&)
                              {
                                   cout << "copy Constructor" << endl;
                                   if (itsDownValue == 0)
                                   {
                                      throw xNullDownValue();
                                   }
                                   itsResultValue = itsUpValue/itsDownValue;
                               }
                               
Division::~Division ()
                      {
                               cout << "Destructor" << endl;
                      }
                               

int main(int argc, char *argv[])
{
    try
    {
        Division first;
        cout << first.GetResultValue () << endl;
    }
    catch (Division::xNullDownValue)
    {
        cout << "Down value is Null!" << endl;
    }
    catch (...)
    {
        cout << "error!" << endl;
    }
    cout << "Press the enter key to continue ...";
    cin.get();
    return 0;
}

kopirovaci konstruktor se vola, kdyz objektu prirazujes kopii jineho objektu stejneho typu

 zkus tohle:

#include <iostream>

using namespace std;

class Division
{
      public:
            Division ();
            Division (Division&);
            ~Division ();
            float GetDownValue () const {return itsDownValue;}
            float GetResultValue () const {return itsResultValue;}
            float GetUpValue () const {return itsUpValue;}
            void SetDownValue (float downValue) {itsDownValue = downValue;}
            void SetUpValue (float upValue) {itsUpValue = upValue;}
            class xNullDownValue {};
      private:
              float itsDownValue;
              float itsResultValue;
              float itsUpValue;
};

Division::Division ():
                      itsDownValue(1),
                      itsResultValue(0),
                      itsUpValue(0)
                      {
                                   cout << "Constructor" << endl;
                      }

Division::Division (Division& objekt)
                              {
                                   cout << "copy Constructor" << endl;
                                   if (objekt.itsDownValue == 0)
                                   {
                                      throw 0;
                                   }
                                   itsResultValue = itsUpValue/itsDownValue;
                               }
                               
Division::~Division ()
                      {
                               cout << "Destructor" << endl;
                      }
                               

int main(int argc, char *argv[])
{
    try
    {
        Division first;
        first.SetDownValue(0);
        Division two = first;
    }
    catch (int)
    {
        cout << "Down value is Null!" << endl;
    }
    catch (...)
    {
        cout << "error!" << endl;
    }
    cout << "Press the enter key to continue ...";
    cin.get();
    return 0;
}

#3 fnenks
Ok dík. Proč jste měnil to throw, když to funguje stejně? No prostě bych rád pokračoval dál v studiu, a když občas narazím na něco, co mi není jasné, tak bych se rád zeptal nebo vyhledal. :-)

Ještě by mě zajímalo, jak nejlépe udělat to dělení. Abych to nemusel dávat do kopírovacího constructoru. Když jsem se vzorec pokusil vložit do funkce GetResultValue (), tak mě to napsalo:

30 C:\Users\VereWolf2\Desktop\Untitled1.cpp:49 assignment of member 'Division::itsResultValue' in read-only object

#include <iostream>

using namespace std;

class Division
{
      public:
            Division ();
            Division (Division&);
            ~Division ();
            float GetDownValue () const {return itsDownValue;}
            float GetResultValue () const;
            float GetUpValue () const {return itsUpValue;}
            void SetDownValue (float downValue) {itsDownValue = downValue;}
            void SetUpValue (float upValue) {itsUpValue = upValue;}
            class xNullDownValue {};
      private:
              float itsDownValue;
              float itsResultValue;
              float itsUpValue;
};

Division::Division ():
                      itsDownValue(1),
                      itsResultValue(0),
                      itsUpValue(0)
                      {
                                   cout << "Constructor" << endl;
                      }

Division::Division (Division& object)
                              {
                                   cout << "copy Constructor" << endl;
                                   if (object.itsDownValue == 0)
                                   {
                                      throw xNullDownValue();
                                   }
                                   itsDownValue = object.GetDownValue ();
                                   itsUpValue = object.GetUpValue ();
                                   itsResultValue = itsUpValue / itsDownValue;
                               }
                               
Division::~Division ()
                      {
                               cout << "Destructor" << endl;
                      }
float Division::GetResultValue () const
{
    itsResultValue = itsUpValue / itsDownValu;
    return itsResultValue;
}

int main(int argc, char *argv[])
{
    try
    {
        float down,up;
        Division first;
        cout << "Napis horni hodnotu: ";
        cin >> up;
        cout << endl;
        first.SetUpValue(up);
        cout << "Napis dolni hodnotu: ";
        cin >> down;
        cout << endl;
        first.SetDownValue(down);
        Division two = first;
        cout << first.GetResultValue () << endl;
        cout << two.GetResultValue () << endl;
    }
    catch (Division::xNullDownValue)
    {
        cout << "Down value is Null!" << endl;
    }
    catch (...)
    {
        cout << "error!" << endl;
    }
    cout << "Press the enter key to continue ...";
    cin.get();
    cin.get();
    return 0;
}

Všude za GetResultValue odstraň const

#6 Martin Kozibrátka
Dík.