I want to get a specific object in a class in C++. I looked into multiple sites and it seems my question is unique. Okay here's my code.
In House.h
#include <string>
using namespace std;
class House
{
string Name;
int Health;
public:
House(string a, int h);
void GetHouseStats();
void DamageHouse(int d);
~House();
};
in House.cpp
#include "House.h"
#include <iostream>
House::House(string a, int h)
{
Name = a;
Health = h;
}
void House::DamageHouse(int d) {
Health -= d;
cout << "Your " << Name << " has " << Health << " left."<<endl;
}
void House::GetHouseStats() {
cout << Name<<endl;
cout << Health;
}
House::~House()
{
}
in Source.cpp
#include <iostream>
#include "House.h"
using namespace std;
int main()
{
House Kubo("Bahay Kubo", 2);
Kubo.DamageHouse(1);
}
I have House Kubo as my first object. I would like to save the person's houses into a file but my problem is How can I pass the object's name into the function so that save its data into a file? I can manually place the Kubo and do so as
PlayerHouse = Kubo.Name;
But what if I don't know which house I should save? Like instead of typing down
PlayerHouse = Apartment.Name;//2nd house
PlayerHouse = Modern.Name;//3rd house
Can I use an function argument to place the object's name into PlayerHouse? Like this
void SetHouseName(type object){
PlayerHouse = object.Name;
}
Few ways in which this can be done .. is keeping all created object in a container and then access access the container to get the object in and pass it a function which will write it to a file .
Also if you do not want to maintain the container what you have mentioned about using the function will also work fine
Of course, but if you are going to save the Name of the house anyway, why don't you just ask for a std::string in the first place and then pass the Name to that function?
void SetHouseName(std::string name)
{
PlayerHouse = name;
}
If this is outside your House class you need to create a method to expose the Name member of House though, or just make it public.
To answer your initial question, just as how you would pass built-in types, you can do the same for your House type :
void SetHouseName(House house)
{
PlayerHouse = house.Name;
}
Related
Below is code for a simple book list with a class to store book names and isbn numbers into an overloaded function using a vector. This program runs fine and I can test it by returning a specific name (or isbn) using an accessor function from my class.
Question: I tried calling (instantiating?) a constructor with parameters from my class but it would not work, so I commented it out. Yet I was still able to run the program without error. From my main below - //BookData bkDataObj(bookName, isbn);
From watching tutorials, I thought I always had to make an object for a specific constructor from a class that I needed to call? My program definitely still uses my overloaded constructor and function declaration BookData(string, int); without making an object for it in main first.
Thanks for any help or input on this matter.
Main
#include <iostream>
#include <string>
#include <vector>
#include "BookData.h"
using namespace std;
int main()
{
string bookName[] = { "Neuromancer", "The Expanse", "Do Androids Dream of Electric Sheep?", "DUNE" };
int isbn[] = { 345404475, 441569595, 316129089, 441172717 };
//BookData bkDataObj(bookName, isbn); //how did program run without instantiating object for class?
vector <BookData> bookDataArr;
int arrayLength = sizeof(bookName) / sizeof(string);
for (int i = 0; i < arrayLength; i++) {
bookDataArr.push_back(BookData(bookName[i], isbn[i]));
}
cout << "Book 4 is: " << bookDataArr[3].getBookNameCl(); //test if works
return 0;
}
BookData.h
#include <iostream>
#include <string>
using namespace std;
class BookData
{
public:
BookData();
BookData(string, int); //wasn't I supposed to make an object for this constructor in my main?
string getBookNameCl();
int getIsbnCl();
private:
string bookNameCl;
int isbnCl;
};
BookData.cpp
#include "BookData.h"
BookData::BookData() {
bookNameCl = " ";
isbnCl = 0;
}
BookData::BookData(string bookNameOL, int isbnOL) { //how did I use this function
bookNameCl = bookNameOL; //definition without an object in main?
isbnCl = isbnOL;
}
string BookData::getBookNameCl() { //can still return a book name
return bookNameCl;
}
int BookData::getIsbnCl() {
return isbnCl;
}
I am trying to create a simple program in C++ that creates lists of movies using 2 classes: Movie, which contains details of one movie, and Movies, which contains a name and a vector of Movie objects. The whole point is that the user should only interact with the class Movies, therefore I have chosen to make all the members (both data and methods) of the Movie class private.
I keep getting the following error if I let Movie::~Movie() as it is, but if I comment it in both .h and .cpp, it works just fine.
I have explicitly made Movies class a friend of Movie class, so it can access all its members.
error from Visual Studio Community 2019
Movie.h:
#pragma once
#include<iostream>
#include<string>
class Movie
{
friend class Movies;
private:
std::string name;
std::string rating;
int watchedCounter;
int userRating;
std::string userOpinion;
// methods also private because the user should only interact with the Movies class, which is a friend of class Movie
std::string get_name() const;
Movie(std::string nameVal = "Default Name", std::string ratingVal = "Default Rating", int watchedCounterVal = 0, int userRatingVal = 0, std::string userOpinionVal = "");
~Movie();
};
Movie.cpp:
#include "Movie.h"
// Name getter
std::string Movie::get_name() const
{
return this->name;
}
///*
// Destructor
Movie::~Movie()
{
std::cout << "Movie destructor called for: " << this->name << std::endl;
}
//*/
// Constructor
Movie::Movie(std::string nameVal, std::string ratingVal, int watchedCounterVal, int userRatingVal, std::string userOpinionVal) : name{ nameVal }, rating{ ratingVal }, watchedCounter{ watchedCounterVal }, userRating{ userRatingVal }, userOpinion{userOpinionVal}
{
std::cout << "Movie constructor called for: " << name << std::endl;
}
Movies.h:
#pragma once
#include<iostream>
#include<vector>
#include "Movie.h"
class Movies
{
private:
std::string listName;
std::vector<Movie> vectOfMovies;
static int listNumber;
public:
Movies(std::string listNameVal = "Default User's Movie List ");
~Movies();
std::string get_listName() const;
void addMovie(Movie m);
};
Movies.cpp:
#include<string>
#include "Movies.h"
int Movies::listNumber = 0;
// Constructor
Movies::Movies(std::string listNameVal) : listName{listNameVal}
{
++listNumber;
listName += std::to_string(listNumber);
std::cout << "MovieS constructor called for: " << listName << std::endl;
}
// Destructor
Movies::~Movies()
{
std::cout << "MovieS destructor called for: " << listName << std::endl;
}
std::string Movies::get_listName() const
{
return this->listName;
}
//Add movie to list of movies
void Movies::addMovie(Movie m)
{
this->vectOfMovies.push_back(m);
}
And the main .cpp file:
#include <iostream>
// #include "Movie.h"
#include "Movies.h"
int main()
{
Movies moviesObj;
moviesObj.get_listName();
return 0;
}
If the constructor/destructor is declared as private, then the class cannot be instantiated. If the destructor is private, then the object can only be deleted from inside the class as well. Also, it prevents the class from being inherited (or at least, prevent the inherited class from being instantiated/destroyed at all).
The use of having destructor as private:
Any time you want some other class to be responsible for the life cycle of your class' objects, or you have reason to prevent the destruction of an object, you can make the destructor private.
For instance, if you're doing some sort of reference counting thing, you can have the object (or manager that has been "friend"ed) responsible for counting the number of references to itself and delete it when the number hits zero. A private dtor would prevent anybody else from deleting it when there were still references to it.
For another instance, what if you have an object that has a manager (or itself) that may destroy it or may decline to destroy it depending on other conditions in the program, such as a database connection being open or a file being written. You could have a "request_delete" method in the class or the manager that will check that condition and it will either delete or decline, and return a status telling you what it did. That's far more flexible that just calling "delete".
So, I suggest that you could declare ~Movie(); as public. Then, the problem will be solved.
Im completely new to C++ and im trying to make a very simple text based combat system, but I keep getting the error: "objPlayer was not declared in this scope".
All the code is written before the main() function:
#include <iostream>
using namespace std;
//DECLARE THE UNIT CLASS
class generalUnit {
public:
int health; //the amount of health the unit has
};
//DECLARE THE PLAYER THOUGH THE UNIT CLASS
void generatePlayer() {
generalUnit objPlayer;
int objPlayer.health = 100;
}
//DECLARE AND INITIALIZE ALL COMMANDS
//CHECK STATS
void comCheckStats() {
cout << objPlayer.health << endl;
}
You don't have to create a variable inside a class pointing to the object of that class you are using. It is already declared and is called this.
With operator -> you can then access member variables from this. Like so:
#include <iostream>
#include <string>
using namespace std;
class Player
{
public:
int health;
// this is constructor
Player(int health_at_start)
{
this->health = health_at_start;
}
void comCheckStats()
{
cout << this->health << '\n';
}
};
int main()
{
// create player with 100 health
Player p1(100);
p1.comCheckStats();
// create player with 200 health
Player p2(200);
p2.comCheckStats();
}
As you can see, I am using something called constructor to create new instance of Player. It is just function without return type, declared with the same name as the class. It initializes member variable starting data and you can pass some values to it too.
Here's my code:
#include <iostream>
#include <string>
class Human
{
public:
std::string * name = new std::string();
void introduce();
};
void Human::introduce()
{
std::cout << "Hello, my name is " << Human::name << std::endl;
}
int main()
{
Human * martha;
martha->name = new std::string("Martha");
martha->introduce();
return 0;
}
Well, it's supposed to print a message out like:
"Hello, my name is Martha" but it doesn't print neither the "Hello, my name is" string or the "Martha" name. Why does it occur?
The fix is simple and is to completely remove all pointers; see the code below. There are a number of issues with your code that I could address in detail, including memory leaks, uninitialized variables, and general misuse of pointers, but it seems that you're possibly coming from a different language background and should spend time learning good practice and the important semantics and idioms in modern C++ from a good C++ book.
#include <iostream>
#include <string>
class Human
{
public:
std::string name;
void introduce();
};
void Human::introduce()
{
std::cout << "Hello, my name is " << name << std::endl;
}
int main()
{
Human martha;
martha.name = "Martha";
martha.introduce();
return 0;
}
Few modifications are required to the code.
Updated code along with the comments to the change made are included below.
#include <iostream>
#include <string>
class Human
{
public:
//Removed pointer to a string
//Cannot have an instantiation inside class declaration
//std::string * name = new std::string();
//Instead have a string member variable
std::string name;
void introduce();
};
void Human::introduce()
{
//Human::name not required this is a member function
//of the same class
std::cout << "Hello, my name is " << name << std::endl;
}
int main()
{
Human *martha = new Human();
//Assign a constant string to string member variable
martha->name = "Martha";
martha->introduce();
return 0;
}
As suggested by #alter igel - The Definitive C++ Book Guide and List would be a good place to start.
#include <iostream>
#include <string>
class Human {
public:
void Human(std::string* n) { name = n; }
void introduce();
private:
std::string* name;
};
void Human::introduce() {
std::cout << "Hello, my name is " << name << std::endl;
}
int main() {
Human* martha = new Human(new std:string("Martha"));
martha->introduce();
return 0;
}
Try that. The difference is that you don't initialise the variable in the class definition, and you initialise the name with the constructor. You can split the method definition out into it's own section, but it's only one line and is fine being inside the class definition.
This question already has answers here:
Updating vector of class objects using push_back in various functions
(2 answers)
Closed 7 years ago.
I am attempting to make a text adventure sort of game, and I would like to avoid a bunch of conditionals, so I am trying to learn about the classes stuff and all that. I have created several classes, but the only ones that pertain to this problem are the Options class and the Items class. My problem is that I am trying to push_back() a object into a vector of the type of that object's class and it apparently doesn't happen yet runs until the vector is attempted to be accessed. This line is in main.cpp. I have researched on this, but I have not been able to find a direct answer, probably because I'm not experienced enough to not know the answer in the first place.
The program is separated into 3 files, main.cpp, class.h, and dec.cpp.
dec.cpp declares class objects and defines their attributes and all that.
main.cpp:
#include <iostream>
#include "class.h"
using namespace std;
#include <vector>
void Option::setinvent(string a, vector<Item> Inventory, Item d)
{
if (a == op1)
{
Inventory.push_back(d);
}
else {
cout << "blank";
}
return;
}
int main()
{
vector<Item> Inventory;
#include "dec.cpp"
Option hi;
hi.op1 = "K";
hi.op2 = "C";
hi.op3 = "L";
hi.mes1 = "Knife";
hi.mes2 = "Clock";
hi.mes3 = "Leopard!!";
string input1;
while (input1 != "quit")
{
cout << "Enter 'quit' at anytime to exit.";
cout << "You are in a world. It is weird. You see that there is a bed in the room you're in." << endl;
cout << "There is a [K]nife, [C]lock, and [L]eopard on the bed. Which will you take?" << endl;
cout << "What will you take: ";
cin >> input1;
hi.setinvent(input1, Inventory, Knife);
cout << Inventory[0].name;
cout << "test";
}
}
dec.cpp just declares the Item "Knife" and its attributes, I've tried pushing directly and it works, and the name displays.
class.h
#ifndef INVENTORY_H
#define INVENTORY_H
#include <vector>
class Item
{
public:
double damage;
double siz;
double speed;
std::string name;
};
class Player
{
public:
std::string name;
double health;
double damage;
double defense;
double mana;
};
class Monster
{
public:
double health;
double speed;
double damage;
std::string name;
};
class Room
{
public:
int x;
int y;
std::string item;
std::string type;
};
class Option
{
public:
std::string op1;
std::string op2;
std::string op3;
std::string mes1;
std::string mes2;
std::string mes3;
void setinvent(std::string a, std::vector<Item> c, Item d);
};
#endif
Any help would be greatly appreciated! I realize that the whole structure may need to be changed, but I think that this answer will help even if that may be the case.
My problem is that I am trying to push_back() a object into a vector of the type of that object's class and it apparently doesn't happen yet runs until the vector is attempted to be accessed.
it happen but only inside your setinvent method:
void Option::setinvent(string a, vector<Item> Inventory, Item d)
^^^^^^^^^^^^ - passed by value
Inventory is passed by value which means it is a local vector variable in setinvent function. If you want to modify vector from main function, make it a reference:
void Option::setinvent(string a, vector<Item>& Inventory, Item d)
^^^^^^^^^^^^ - passed by reference, modifies vector from main
now Inventory is local reference variable. Also dont forget to change setinvent declaration in header file.