C / C++ / MFC Discussion Boards

Re: Problem creating an array of "class"

Richard MacCutchan7-Sep-22 5:10

Richard MacCutchan

7-Sep-22 5:10

The array variable needs to point to an array of pointers, so the syntax needs to be:

C++

anagrafica** Arr_ = new anagrafica*[N]; // a pointer to an array of pointers

for (int i = 0; i < N; i++)
{
	Arr_[i] = new anagrafica("ciao", "miao", i*25);
}

Remember that Arr_ is a pointer to the actual array so it will appear to contain only one element. But you can check the contents with another simple loop.

You could make life much simpler for yourself by using one of the STL containers, such as vector<T>.

Re: Problem creating an array of "class"

Roberto64_Ge8-Sep-22 3:55

Roberto64_Ge

8-Sep-22 3:55

ok, i better checked, so thank you. Now, how is the syntax to access the method of any instance (of the class) pointed by the i element af Arr_. I don't find the way to do that. I mean that I need to do something like

Example : Arr_[i].setChiave(3)

By the way, may I call a method , example setNome(stringaNome) from within another method?

modified 8-Sep-22 10:22am.

Re: Problem creating an array of "class"

Greg Utas8-Sep-22 4:24

Greg Utas

8-Sep-22 4:24

Arr_[i]->setChiave(3)

EDIT: And sure, one method can call another, subject to access controls (public, protected, private).

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Re: Problem creating an array of "class"

Roberto64_Ge8-Sep-22 4:32

Roberto64_Ge

8-Sep-22 4:32

OK thanks.

By the way, may I call a method , example setNome(stringaNome) from within another method? I attach here three methods of the class, the greater calling the two small.

C++

void anagrafica::setNome(string n_)
   {
   nome_cifrato=n_;
   }

void anagrafica::setCognome(string c_)
   {
   cognome_cifrato=c_;
   }

void anagrafica::codifica(string nome_chiaro, string cognome_chiaro, int chiave)
{ 
 char car;
 nome_cifrato = "";
 cognome_cifrato = "";
 for (int i=0;i <nome_chiaro.length();i++)
    {
     car = nome_chiaro[i] + chiave;
     nome_cifrato = nome_cifrato + car;
     cout<<"carattere "<<i<<" n in chiaro "<<nome_chiaro[i]<<" chiave  "<<chiave<<" cifrato "<<car<<" nome incostruzione "<<nome_cifrato<<endl;
    }
 setNome(nome_cifrato);     
 for (int i=0; i<cognome_chiaro.length();i++)
    {
     car = cognome_chiaro[i] + chiave;
     cognome_cifrato = cognome_cifrato + car;
     cout<<"carattere "<<i<<" c in chiaro "<<cognome_chiaro[i]<<" chiave  "<<chiave<<" cifrato "<<car<<" cognome incostruzione "<<cognome_cifrato<<endl;
    }
 setCognome(cognome_cifrato);   
}

The two lines of code hghlighted have no effects.

Re: Problem creating an array of "class"

Greg Utas8-Sep-22 6:59

Greg Utas

8-Sep-22 6:59

Those lines have no effect because the default in C++ is to pass an argument by value. That is, to make a copy of it. If you want to modify the data that is passed to the function, it must be passed by reference; another option is to pass a pointer to the argument. To pass by reference, you append a & to the argument's type. So, you need to change your two small functions like this:

C++

void anagrafica::setNome(string& n_)
   {
   nome_cifrato=n_;
   }

void anagrafica::setCognome(string& c_)
   {
   cognome_cifrato=c_;
   }

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modified 8-Sep-22 13:10pm.

Re: Problem creating an array of "class"

Richard MacCutchan8-Sep-22 23:57

Richard MacCutchan

8-Sep-22 23:57

That will not make any difference. I have just tested the code and those methods both do what they are supposed to. The issue is more complex due to the confused (and confusing) nature of this code.

Re: Problem creating an array of "class"

Richard MacCutchan8-Sep-22 4:32

Richard MacCutchan

8-Sep-22 4:32

Roberto64_Ge wrote:
Example : Arr_[i].setChiave(3)

Yes, as a simple test would show you.

Roberto64_Ge wrote:
may I call a method , example setNome(stringaNome) from within another method?

Yes again. All methods* within a class may be called from other methods, whether they are private or public. *But you cannot call non-static from static methods, as the non-statics need an object reference.

Re: Problem creating an array of "class"

Roberto64_Ge8-Sep-22 4:36

Roberto64_Ge

8-Sep-22 4:36

if I use double pointer compiler don't let me use that syntax.

Re: Problem creating an array of "class"

Richard MacCutchan8-Sep-22 4:53

Richard MacCutchan

8-Sep-22 4:53

What do you mean by, "double pointer"? If something does not work then please show the actual code and the error message(s).

Re: Problem creating an array of "class"

Roberto64_Ge8-Sep-22 5:18

Roberto64_Ge

8-Sep-22 5:18

i do not know how to quote a previous answer. Anyway you suggested me to use a pointer to an array of pointers so we did

anagrafica **Arr_ = new anagrafica*[N];

But in this case compiler didn't let me access the method in this way :

Arr_[i].setChiave(3);

For that reason I asked for the correct syntax. Meanwhile I was waiting your reply I decided to try and so I went back to the first version temporarily and this is working, with respect to my first question " why I cannot see all the array elements?".
With this I mean that, also with my first version, if I access Arr_[i] during the debug (within the relevant window "Control expression". I guess this is the correct translation from Italian) I see all the different instances of the class in each element of the array Arr_. I attach here the code of the first version.

With this version running then I get a new malfunction that is that when I call the method for cifrating the true name and surname, from within this method I call the two methods to set the name and the surname, setNome and setCognome but this has no effects. If preferred I will attach the complete solution.

C++

<pre>anagrafica* Arr_ = new anagrafica[N];

for (int i = 0; i < N; i++)
{
	Arr_[i] = anagrafica("ciao", "miao", i*25);
}

for (int i=0; i<N; i++)
{
 file>>chiave;
 file>>n;
 file>>c;
 Arr_[i].setChiave(chiave);
 cod(Arr_[i],n,c,chiave);
}
for (int i=0; i<N; i++)
	Arr_[i].stampa();

Re: Problem creating an array of "class"

Richard MacCutchan8-Sep-22 5:25

Richard MacCutchan

8-Sep-22 5:25

C++

Arr_[i].setChiave(3);

Sorry, I misread that. Arr_[i] is a pointer so you need to use the correct pointer dereferencing syntax:

C++

Arr_[i]->setChiave(3);

Re: Problem creating an array of "class"

Roberto64_Ge8-Sep-22 5:27

Roberto64_Ge

8-Sep-22 5:27

Ok i realized that. thank you very much. What about the other problem? Methods ....

Re: Problem creating an array of "class"

Richard MacCutchan8-Sep-22 5:17

Richard MacCutchan

8-Sep-22 5:17

I have commented out all the parts of your code that are not needed to create a simple test. The result is as follows:

C++

// header file
#include<iostream>
#include<string>
using namespace std;

 class anagrafica
 {
   private:
   
   string nome_cifrato;  
   string cognome_cifrato;   
   int chiave_cifratura;
   
   public : 
   
   anagrafica(string a, string b, int c); //costruttore
   
  //  void setNome(string );
   
  //  void setCognome(string );
   
  //  string getNome();
   
  //  string getCognome();
   
  //  void codifica(string , string , int );
   
  //  void decodifica();
   
    void setChiave(int);
    void print();
    
  //  int getChiave();
   
  //  void stampa();
   
   
 };

C++

// implementation
#include "Anagrafica.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

// void cod (anagrafica arr,string n, string c,int chiave)
// { arr.codifica(n,c,chiave); }
 
// void decod (anagrafica arr)
// { arr.decodifica(); }

anagrafica::anagrafica(string a, string b, int c) //costruttore
{
   nome_cifrato = a;  
   cognome_cifrato = b;   
   chiave_cifratura = c;
}

void anagrafica::setChiave(int a)
{
	chiave_cifratura = a;
}

// added to show the results
void anagrafica::print()
{
	cout << nome_cifrato << " " << cognome_cifrato << " " << chiave_cifratura << endl;
}

int main()
{
// ifstream file; 
// file.open("input.txt"); 
int N = 4; // create just four entries
//string n,c;

// int chiave;
// int chiave_input;
// file>>N; 
// cout<<N<<endl;

anagrafica** Arr_ = new anagrafica*[N];

for (int i = 0; i < N; i++)
{
	Arr_[i] = new anagrafica("ciao", "miao", i*25);
}

for (int i = 0; i < N; i++)
{
	Arr_[i]->print();
}

// for (int i=0; i<N; i++)
// {
//  file>>chiave;
//  file>>n;
//  file>>c;
//  //Arr_[i].setChiave(chiave);
//  //cod(Arr_[i],n,c,chiave);
// }
// for (int i=0; i<N; i++)
// 	//Arr_[i].stampa();

// cout<<"inserire un valore intero"<<endl;
// cin>>chiave_input;

}

Re: Problem creating an array of "class"

Roberto64_Ge8-Sep-22 5:26

Roberto64_Ge

8-Sep-22 5:26

Ok , so the syntax is not

Arr_[i].setChiave(3)

but

Arr_[i]->setChiave(3)

as per Greg Utas and your new indication.
As I wrote I would say that also the version

C++

<pre>anagrafica* Arr_ = new anagrafica[N];

for (int i = 0; i < N; i++)
{
	Arr_[i] = anagrafica("ciao", "miao", i*25);
}

is working the same. Then I have the further problem of the two methods for setting cifrated name and surname tha have no effects.

I see that there is some problem of synchronizations with the replies. But ok syntax has been clarified.

Re: Problem creating an array of "class"

Richard MacCutchan8-Sep-22 5:38

Richard MacCutchan

8-Sep-22 5:38

You have declared a number of methods in your header file but you have not added their implementation to the .cpp source. In my sample code above you can see the implementation for the setChiave method. You need to do the same for all the other methods declared in the class.

Re: Problem creating an array of "class"

Roberto64_Ge8-Sep-22 5:43

Roberto64_Ge

8-Sep-22 5:43

I attach the method file .cpp

C++

#include "Anagrafica.h"
#include <iostream>
#include <string>

using namespace std;



anagrafica::anagrafica(string name,string surname, int key)
{
 nome_cifrato=name;
 cognome_cifrato=surname;
 chiave_cifratura=key;
}

void anagrafica::setNome(string n_)
   {
   nome_cifrato=n_;
   }
void anagrafica::setCognome(string c_)
   {
   cognome_cifrato=c_;
   }

   
string anagrafica::getNome()
   {
   return nome_cifrato;
   }
string anagrafica::getCognome()
   {
   return cognome_cifrato;
   }

int anagrafica::getChiave()
{
 return chiave_cifratura;
 }

void anagrafica::setChiave(int c)
{
 chiave_cifratura=c;
}

void anagrafica::stampa()
{
    string nom = nome_cifrato;
    string cog = cognome_cifrato;
 cout<<" nome  cifrato "<<nom;
 cout<<" cognome  cifrato "<<cog<<endl;
}


void anagrafica::codifica(string nome_chiaro, string cognome_chiaro, int chiave)
{ 
 char car;
 nome_cifrato = "";
 cognome_cifrato = "";
 for (int i=0;i <nome_chiaro.length();i++)
    {
     car = nome_chiaro[i] + chiave;
     nome_cifrato = nome_cifrato + car;
     cout<<"carattere "<<i<<" n in chiaro "<<nome_chiaro[i]<<" chiave  "<<chiave<<" cifrato "<<car<<" nome incostruzione "<<nome_cifrato<<endl;
    }
 setNome(nome_cifrato);     
 for (int i=0; i<cognome_chiaro.length();i++)
    {
     car = cognome_chiaro[i] + chiave;
     cognome_cifrato = cognome_cifrato + car;
     cout<<"carattere "<<i<<" c in chiaro "<<cognome_chiaro[i]<<" chiave  "<<chiave<<" cifrato "<<car<<" cognome incostruzione "<<cognome_cifrato<<endl;
    }
 setCognome(cognome_cifrato);   
}
   
void anagrafica::decodifica()
{ 

 char car;
 string nome_chiaro = "";
 string cognome_chiaro = "";
 for (int i=0;i <nome_cifrato.length();i++)
    {
     car = nome_cifrato[i] - chiave_cifratura;
     nome_chiaro = nome_chiaro + car;
     cout<<"carattere "<<i<<" n in cifrato "<<nome_cifrato[i]<<" chiave  "<<chiave_cifratura<<" chiaro "<<car<<" nome incostruzione "<<nome_chiaro<<endl;
    }
 cout<<" nome in chiaro "<<nome_chiaro;     
 for (int i=0; i<cognome_cifrato.length();i++)
    {
     car = cognome_cifrato[i] - chiave_cifratura;
     cognome_chiaro = cognome_chiaro + car;
     cout<<"carattere "<<i<<" c in cifrato "<<cognome_cifrato[i]<<" chiave  "<<chiave_cifratura<<" chiaro "<<car<<" cognome incostruzione "<<cognome_chiaro<<endl;
    }
 cout<<" cognome in chiaro "<<cognome_chiaro<<endl; 
}

I can't understand where is the error.

Re: Problem creating an array of "class"

Roberto64_Ge8-Sep-22 5:37

Roberto64_Ge

8-Sep-22 5:37

Clarified the syntax problem I resume here.
The code works also in this way ::

C++

anagrafica* Arr_ = new anagrafica[N];

for (int i = 0; i < N; i++)
{
	Arr_[i] = anagrafica("ciao", "miao", i*25);
}

for (int i=0; i<N; i++)
{
 file>>chiave;
 file>>n;
 file>>c;
 Arr_[i].setChiave(chiave);
 cod(Arr_[i],n,c,chiave);
}
for (int i=0; i<N; i++)
	Arr_[i].stampa();

Because I can see all the Arr_ elements containing instances of the class. But two methods recalled from one other method do not heve effects.

Re: Problem creating an array of "class"

Richard MacCutchan8-Sep-22 5:45

Richard MacCutchan

8-Sep-22 5:45

I think this thread is getting confused (I certainly am). I suggest you start a new thread and post the actual code that you are now using, and explain what methods do not work.

Re: Problem creating an array of "class"

Roberto64_Ge8-Sep-22 8:04

Roberto64_Ge

8-Sep-22 8:04

header

C++

#include<iostream>
#include<string>
using namespace std;

 class anagrafica
 {
   private:
   
   string nome_cifrato;  
   string cognome_cifrato;   
   int chiave_cifratura;
   
   public : 
   
   anagrafica(string ="", string ="", int=0); //costruttore
   
   void setNome(string );
   
   void setCognome(string );
   
   string getNome();
   
   string getCognome();
   
   void codifica(string , string , int );
   
   void decodifica();
   
   void setChiave(int);
    
   int getChiave();
   
   void stampa();
   
   
 };

methods

C++

#include "Anagrafica.h"
#include <iostream>
#include <string>

using namespace std;



anagrafica::anagrafica(string name,string surname, int key)
{
 nome_cifrato=name;
 cognome_cifrato=surname;
 chiave_cifratura=key;
}

void anagrafica::setNome(string n_)
   {
   nome_cifrato=n_;
   }
void anagrafica::setCognome(string c_)
   {
   cognome_cifrato=c_;
   }

   
string anagrafica::getNome()
   {
   return nome_cifrato;
   }
string anagrafica::getCognome()
   {
   return cognome_cifrato;
   }

int anagrafica::getChiave()
{
 return chiave_cifratura;
 }

void anagrafica::setChiave(int c)
{
 chiave_cifratura=c;
}

void anagrafica::stampa()
{
    string nom = nome_cifrato;
    string cog = cognome_cifrato;
 cout<<" nome  cifrato "<<nom;
 cout<<" cognome  cifrato "<<cog<<endl;
}


void anagrafica::codifica(string nome_chiaro, string cognome_chiaro, int chiave)
{ 
 char car;
 nome_cifrato = "";
 cognome_cifrato = "";
 for (int i=0;i <nome_chiaro.length();i++)
    {
     car = nome_chiaro[i] + chiave;
     nome_cifrato = nome_cifrato + car;
     cout<<"carattere "<<i<<" n in chiaro "<<nome_chiaro[i]<<" chiave  "<<chiave<<" cifrato "<<car<<" nome incostruzione "<<nome_cifrato<<endl;
    }
 setNome(nome_cifrato);     
 for (int i=0; i<cognome_chiaro.length();i++)
    {
     car = cognome_chiaro[i] + chiave;
     cognome_cifrato = cognome_cifrato + car;
     cout<<"carattere "<<i<<" c in chiaro "<<cognome_chiaro[i]<<" chiave  "<<chiave<<" cifrato "<<car<<" cognome incostruzione "<<cognome_cifrato<<endl;
    }
 setCognome(cognome_cifrato);   
}
   
void anagrafica::decodifica()
{ 

 char car;
 string nome_chiaro = "";
 string cognome_chiaro = "";
 for (int i=0;i <nome_cifrato.length();i++)
    {
     car = nome_cifrato[i] - chiave_cifratura;
     nome_chiaro = nome_chiaro + car;
     cout<<"carattere "<<i<<" n in cifrato "<<nome_cifrato[i]<<" chiave  "<<chiave_cifratura<<" chiaro "<<car<<" nome incostruzione "<<nome_chiaro<<endl;
    }
 cout<<" nome in chiaro "<<nome_chiaro;     
 for (int i=0; i<cognome_cifrato.length();i++)
    {
     car = cognome_cifrato[i] - chiave_cifratura;
     cognome_chiaro = cognome_chiaro + car;
     cout<<"carattere "<<i<<" c in cifrato "<<cognome_cifrato[i]<<" chiave  "<<chiave_cifratura<<" chiaro "<<car<<" cognome incostruzione "<<cognome_chiaro<<endl;
    }
 cout<<" cognome in chiaro "<<cognome_chiaro<<endl; 
}

main

C++

#include "Anagrafica.h"
#include <iostream>
#include <fstream>
#include <string>


using namespace std;


 
void cod (anagrafica arr,string n, string c,int chiave)
{

arr.codifica(n,c,chiave); 

}
 
 
void decod (anagrafica arr)
{

arr.decodifica(); 

}
 
int main()
{
ifstream file; // dichiarazione del file
file.open("input.txt"); //apertura del file

int N;
string n,c;

int chiave;
int chiave_input;

file>>N; //legge il primo numero
cout<<N<<endl;

anagrafica* Arr_ = new anagrafica[N];
// this is only for test
for (int i = 0; i < N; i++)
{
	Arr_[i] = anagrafica("ciao", "miao", i*25);
}
for (int i=0; i<N; i++)
{
 file>>chiave;
 file>>n;
 file>>c;
 Arr_[i].setChiave(chiave);
 cod(Arr_[i],n,c,chiave);
}
for (int i=0; i<N; i++)
	Arr_[i].stampa();

cout<<"inserire un valore intero"<<endl;
cin>>chiave_input;

for (int i=0; i<N; i++)
{
 cout<<" chiave  "<< Arr_[i].getChiave()<<endl;
 if(chiave_input== Arr_[i].getChiave())
 decod(Arr_[i]);
}
 
}

That's it.
Highlighted, within method "codifica", the call to the two methods setNome and setCognome that do not work (they do not set any name and surname). The two cout inside "codifica" are only to understand what happens.

The txt file from where to take the data to process is made like this

2 (means how many rows follows)
key1 name1 surname1
key2 name2 surname2

Re: Problem creating an array of "class"

Richard MacCutchan8-Sep-22 23:37

Richard MacCutchan

8-Sep-22 23:37

You need to execute that code through the debugger to see exactly what is happening. I tried to reproduce it and it was passing blank parameters in to the method. I suspect that the problem is where you are reading values from the input file.

[edit]
That method is modifying both variables nome_cifrato and cognome_cifrato inline, and you then call setNome and setCognome. But you have already modified the names so you do not need to call the setter methods. I think you need to look more closely at the design of this application and remove some of the redundancies.

modified 9-Sep-22 6:00am.

Re: Problem creating an array of "class"

Roberto64_Ge9-Sep-22 10:30

Roberto64_Ge

9-Sep-22 10:30

Ok you are right saying that

Richard MacCutchan wrote:
That method is modifying both variables nome_cifrato and cognome_cifrato inline, and you then call setNome and setCognome. But you have already modified the names so you do not need to call the setter methods.

I didn't see it, I get confused writing the code, probably I inteded to use local variables to build cifrated name and surname.

But problem was in this function within the main

C++

void cod (anagrafica arr,string n, string c,int chiave)
{

arr.codifica(n,c,chiave); 

}

that i re-arranged this way

C++

void cod (anagrafica &arr,string n, string c,int chiave)
{

arr.codifica(n,c,chiave); 

}

passing the address to "cod". And about this, I understood the reason (Greg Utas was right about the rules but didn't apply to the real problem because i did not need to change the strings passed to the methods but the instance of the class itself). But now there is another behaviour that confuses me :

In a previous version the following method :

C++

void anagrafica::stampa()
{
 cout<<" nome  cifrato "<<nome_cifrato;
 cout<<" cognome  cifrato "<<cognome_cifrato<<endl;
}

I had to modify in this new version :

C++

void anagrafica::stampa()
{
    string nom = nome_cifrato;
    string cog = cognome_cifrato;
 cout<<" nome  cifrato "<<nom;
 cout<<" cognome  cifrato "<<cog<<endl;
}

because in the first version it was just printing nothing. Now it prints correctly. I just tried without a real knowledge behind, only some kind of sensation but I don't understand why it didn't work before and why it works now.

Anyway thanks for all the efforts/suggestions. I am just starting with c++ in order to help my children in their school exercise.

modified 10-Sep-22 3:10am.

Re: Problem creating an array of "class"

Richard MacCutchan9-Sep-22 22:00

Richard MacCutchan

9-Sep-22 22:00

Roberto64_Ge wrote:
I am just starting with c++ in order to help my children in their school exercise.

Well, I am sorry to have to say this, but what you have created is not a good example of C++ code for them to follow. The two static methods cod and decod serve no purpose other than to call the actual methods of the anagrafica class. So they are totally redundant; you could call the codifica method direct from main. There are a number of other issues that look incorrect to me but I do not have time to teach you C++.

Re: Problem creating an array of "class"

Roberto64_Ge10-Sep-22 0:34

Roberto64_Ge

10-Sep-22 0:34

That was a request (strange to me too. Exercise : implement a function that calls the methods ..., not directly in the main. Could also be that it was some type of cut and paste from other exercises so some error in the exercise definition ). As I said I am starting too so I do what I can and for that reason I am writing here otherwise why should I do this (to ask a forum)? Then I think that everyone is doing something makes mistakes some for distraction (some I did here) and some for poor knowledge (and also here).
But going straight to my last question is there an explanation?
Regards

Re: Problem creating an array of "class"

Richard MacCutchan10-Sep-22 0:47

Richard MacCutchan

10-Sep-22 0:47

I have no idea where that question came from or what it actually says. But I would assume that if you want an explanation then the place where you found it is the best place to ask. The forums here are more for help in diagnosing and fixing specific problems. There are other sites that offer well written tutorials, such as Learn C++ – Skill up with our free tutorials[^] and C++ Tutorial[^].

How can do it in c++?

Member 157580955-Sep-22 6:07

Member 15758095

5-Sep-22 6:07

A project about cars, a library, a pharmacy, a clinic, or ....Etc

Since this project has more than one class
In the project, it has at least 3 properties ( attributes) and contains functions (methods )
Yeshti applied all the concepts of oop in this project
We build at least 5 classes in the project and in each class we apply complex relationships to it and apply the uml scheme to it
It is necessary that in a project report we explain in the report the characteristics of the project, the functions and the goal of the project ,
We use the comments in the editor, in which we explain the description of the functions and the action of each function with an appropriate expression .
The functions we convert to string, and use the principle of inheritance with the determination of private and public variables . It must be in the builder function and the copier function .
And we use get and set

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