Update a class property via setter doesn't work

[Amiplus]

Hello,

I'm trying to exercise c++ coding working on an old style text adventure.
I have created a class for Characters.

i store the created characters in a vector.

static vector<Character> charList;

now the class Character have a method that change the Room position of the character.

void setRoom(int ir) {_inRoom=ir;}

why if i set the charList[i].setRoom(NewRoom) the character retain the room number with which was initialed in the constructor?

Thank you very much

[kevinkjt2000]

This is too small of a snippet for me to be able to tell you why Character::setRoom is not working.

[Amiplus]

Here's the class code

class Character{

  public:
    string _name, _genre="";
    int _inRoom, _status=0;
    bool _activeCharacter=false;
    
    string getName () {return (_name);}
    int getRoom() {return (_inRoom);}
    void setRoom(int ir) {_inRoom=ir;}

};

Character::Character (vector<CObject> my_vector, string name, string genre, int inRoom, bool activeCharacter, int status) {
  _name=name;
  _genre = genre;
  _inRoom=inRoom;
  _activeCharacter = activeCharacter;
  _status=status;
  objects=my_vector;
  My_Objects.clear();

}

in the main()

Character myCharacter(Obj, "Pluto", "Alien", 4, true, 1);
//note the 4 is the room.

charList.push_back(myCharacter)

myCharacter[i].setRoom(3); //work, but if i later call

int myCharRoom=myCharacter[i].getRoom(); 

i get 4 as a result

[AbstractionAnon]

There is nothing wrong with setRoom().

Show us where you modify an instance of Character that setRoom() doesn't work.

Apparently unrelated, but of concern:
Line 14: my_vector is passed by value. When you store it in objects at line 20, you're storing a copy. Any changes made to objects won't be reflected in my_vector, or the vector that was passed to the constructor.

[Amiplus]

static void charactersMoving(vector<CCharacter> charList) {

    string name;
    int aRoom=0;
    int roomExit;
for (int i=0; i< charList.size(); i++) {

    if (charList[i]._activeCharacter==true) {
    // skip i don't want to move the active character to another room, but only    the inactive character
    }else{
        name=charList[i].getName();
        aRoom=charList[i].getRoom();
        roomExit=GetRoomExit(); //provide a random possible exist

     }
            charList[i].setRoom(randomExit);
}


}

as for the suggestion on line 14, could you please explain it better?

[kevinkjt2000]

Line 14: my_vector is passed by value. When you store it in objects at line 20, you're storing a copy. Any changes made to objects won't be reflected in my_vector, or the vector that was passed to the constructor.

Possibly good for the constructor, but definitely bad for the charactersMoving function. When you modify copies in the charactersMoving function, the originals someplace else never reflect the changes that were made to the copy.
http://courses.washington.edu/css342/zander/css332/passby.html

[Amiplus]

Thank you for the infos.

What about this?

"why if i set the charList[i].setRoom(NewRoom) the character retain the room number with which was initialed in the constructor?"

really struggling with this.

[kevinkjt2000]

Amiplus wrote:

"why if i set the charList[i].setRoom(NewRoom) the character retain the room number with which was initialed in the constructor?"

really struggling with this.

kevinkjt2000 wrote:

When you modify copies in the charactersMoving function, the originals someplace else never reflect the changes that were made to the copy.

So, when you modify the original in the constructor, you keep the changes because it is original and not a passed by value copy.

[Amiplus]

Thank you.

How to solve this?

[keskiverto]

What is the difference of by value and by reference function arguments?

[Amiplus]

Could you please show a modified version of my routine in order to make it work?

[keskiverto]

No. It would hurt you.

Read this tutorial page: http://www.cplusplus.com/doc/tutorial/functions/

After reading that, can you answer my question?

Then, when you can answer my question, can you apply your new knowledge to your problem?

[JLBorges]

Look at this code with the intent to enlarge your understanding.
Doing that has never hurt anyone; it won't hurt you either.

#include <iostream>
#include <vector>
#include <string>

struct character { int room ; character( int r = 0 ) : room(r) {} };

void pass_by_value( std::vector<character> players )
{ for( character& c : players ) c.room = 99 ;  }

void pass_by_reference( std::vector<character>& players )
{ for( character& c : players ) c.room = 99 ;  }

std::vector<character> pass_by_value_return_modified_object( std::vector<character> players )
{
    for( character& c : players ) c.room = 99 ;
    return players ;
}

void print( const std::vector<character>& players )
{
    for( character c : players ) std::cout << c.room << ' ' ;
    std::cout << '\n' ;
}

int main()
{
    {
        std::cout << "------  pass by value ------\n" ;
        std::vector<character> players { 0, 1, 2, 3, 4, 5 } ;
        print(players) ;
        pass_by_value(players) ;
        print(players) ;
    }


    {
        std::cout << "\n------  pass by reference ------\n" ;
        std::vector<character> players { 0, 1, 2, 3, 4, 5 } ;
        print(players) ;
        pass_by_reference(players) ;
        print(players) ;
    }

    {
        std::cout << "\n------  pass by pass by value, return_modified_object------\n" ;
        std::vector<character> players { 0, 1, 2, 3, 4, 5 } ;
        print(players) ;

        std::cout << "ignore the result: " ;
        pass_by_value_return_modified_object(players) ; // ignore the result
        print(players) ;

        std::cout << "update object with the result: " ;
        players = pass_by_value_return_modified_object(players) ; // update object with the result
        print(players) ;
    }
}

http://coliru.stacked-crooked.com/a/5641232f4a9f01e9

[Amiplus]

Thank you for your example: i have to study it, cause it's a little different from my character class using getter and setter.

[Amiplus]

It works now, passing by reference.

Thank you to all. I've read again the tutorial suggested.

Btw, why other settings that i change without passing by reference, but only by values are working?

just for example:

charList.at(i)._activeCharacter=false is working.

This is why i don't call a setter that reside in the Character class, but i set directly the vector<Character> charList in the main()?

[erbisme4]

you need to declare that Character constructor with those parameters in your class. If none is declared, a default (no argument) constructor will be created by the compiler. This is one thing wrong with your code.

[Amiplus]

Parameters are configured

Character::Character (vector<CObject> my_vector, string name, string genre, int inRoom, bool activeCharacter, int status) {