C++ :: Accessing Objects Within Another Object
Feb 8, 2014
I'm currently trying to access a variable contained within a base object from another completely different object and I continually get error messages. I'll attempt to put up the important code since it's contained within fairly large classes. From the Base .cpp file. ObjectPosition:
void ObjectPosition::init(float x,float y, float speed, int boundx, int boundy, float hit, int lives, bool live) {
ObjectPosition::x = x;
ObjectPosition::y = y;
ObjectPosition::speed = speed;
ObjectPosition::boundx = boundx;
ObjectPosition::boundy = boundy;
ObjectPosition::hit = hit;
ObjectPosition::lives = lives;
ObjectPosition::live = live;
}
This is the initialization function for the BaseObject. All objects are inheriting these variables which are Protected within the ObjectPosition class.Then they are initialized within the Pig class thus wise:
void Pig::binit(float sx,float sy, ALLEGRO_BITMAP *simage) {
//Sets all ObjectPosition Variables
ObjectPosition::init(800,900,10,80,40,40,10,true);
smaxFrame = 4;
scurFrame = 0;
[code]...
I tried to initialize the boundx through the pig via pinitx but I get errors and I can't access through the pig to the object position to the boundx.
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May 9, 2013
I have a pointer to a vector of objects, each object has an array and a couple of strings. how to access the data in the objects via the pointer.
Best tree::chooseSplit(vector <pgm> *ptr)
{
Best splits;
cout<<ptr[1].filePath; //not working!!!
}
filepath is a string in the pgm object. i also need to be able to access elements in an array that also exists in pgm.
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Dec 3, 2014
I am working on a video game that is based on a tutorial I found online and I ran into an issue associated with accessing an object's method inside another class object's function without making the object global which seems bad.
Here is basically how the tutorial set things up in the game: The game has a base class called GameObject then there are other child classes that inherit from this class. The GameObject class has all the basic information an object would have that needs rendered on the screen (x/y position, size of bitmap, bitmap, whether or not it is collidable, etc).
One of the child classes SpaceShip, which is the player so it has attributes and methods associated with managing # of lives and points scored.
There are other child classes of GameObjects in the game that need to take life and add points from the SpaceShip object if they collide with the spaceship or other objects.
In the collision handling routine I basically call a function "void Collided(int objectID)" when a game object collides with another. Within the Collided() routine, there is logic that executes code or other functions based on the objectID it collided with. Some of the collisions require taking life from the spaceship or adding points. The way this was accomplished in the tutorial was with function pointers (see Bullet class constructor and collided method for example). Is this really the best way to handle this sort of thing? It seems like there has to be a simpler way than to keep referencing function pointers in any new class I want to add to the game. I realized this when I went to add a method for the spaceship to fire bullets rather than inside my game class.
My Project Source found here: [URL] .....
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Apr 28, 2015
We are coding a Blackjack/21 game. I have a Deck.cpp class, Deck.h, Play.cpp (holds Main), and Card.h (holds card struct). I also have a Hand class/header, but I'm not using it yet. This is what is required per instructor.I am having issues accessing the functions that are in my Deck class. I have tried a few other means to access the class's function, but I've already gotten rid of those. These three are my latest attempts with the specific errors in the comment on the line the error was happening.
ve.
Here is my Deck.h
#pragma once
#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <ctime>
#include <iomanip>
#include "Card.h"
#include "Hand.h"
using namespace std;
class Deck
[Code]...
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Aug 20, 2014
I'm trying to get my head around threading and gui applications for fun, and I've ran into a problem I'm not too sure how to google it correctly or I don't understand the answers given. Basically I'm trying to access GUI item properties (add to a listview). I've been on stackoverflow alot, and I've noticed that accessing these properties is quite difficult. At least, I'm not really understanding how it is supposed to be done.
The following line gives me a null value.
frm.lstChat.Items.Add(newList);
From what I understand I need to access my form object instead of creating a new object window... but I'm not sure how to reference the initial form application.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;
using System.Net.Sockets;
using System.IO;
using System.Threading;
namespace ModBot {
[Code] ....
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Feb 26, 2012
Basically, I've got one object which has to access private data in another object... and can't.
Here's the specifics: I'm writing a little war game program where players deploy units (soldiers, tanks, planes, etc.) onto a gameboard. Players and Units are modeled as objects:
Code:
class GameUnit {
public:
string GetName() {return Name;}
protected:
string Name;
};
class Player {
[Code] ....
Here's the problem: In the above code, Player's ListUnits() function doesn't work because Player can't access GameUnit's GetName() function.
Specifically, here's the compiler's error message:
Code:
In file included from Main.cpp:18:
Player.h: In member function 'void Player::ListUnits()':
Player.h:47: error: 'GetName' undeclared (first use this function)
Player.h:47: error: (Each undeclared identifier is reported only once for each function it appears in.)
I've tested enough to realize that the problem is the GameUnit::GetName() function is a public function within the GameUnit object. Why can't a Player call this function? Making both friend classes of each other doesn't work.
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Dec 21, 2014
I'm working on my first video game. So far I have a few classes in the game starting with the Game class which includes a list of GameObjects (another class). There are several classes that inherit from GameObjects used to implement things like bullets, explosions, various enemy types, etc.
The game essentially iterates through the list of GameObjects to update/render them. I would like to provide access to the Game's list of GameObjects inside another class (like the Bullet class) so I can put new objects on the list. For example, when a bullet hits, I want to add an explosion to the Game's GameObject list it can be updated/rendered.
How this should be setup? I was considering adding a pointer to the Game or GameObject list to the GameObject class (and methods to access it), but I was wondering if there is a better way to set this up?
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Jan 28, 2015
I'm working on collision detection for a game in SFML. I successfully designed a Spatial Partition grid to speed up the collision test, in the following of this tutorial: [URL] ....
But now I have an issue with one aspect of it: Going through a vector of objects and testing all the OTHER objects in the vector against said object. The author puts it into psueudocode here:
For each tick of the clock
For every object in the game
Get all the other objects in the same grid square
For each other object in the same grid square
I have trouble with the last line, because in iterating through a vector I am not sure how to skip over the current object. Here is my own code (a couple of sysntax errors but this is a c++ question not an SFML question):
//for every moveable object
for(int i = 0; i < rects_.size(); i++){
std::vector<sf::RectangleShape> posibleObjects_; //this will be a vector of WorldObjects in a real game
//for every object in that object's gridsquare
for(int j = 0; j < rects_.size(); j++){
if(rects_[i].intersects(rects_[j])){
//collision
} } }
The problem is, a collision will always be reported because somewhere in the vector the object will eventually check against itself which is always a true collision. What is the correct way to do this?
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Feb 10, 2014
I have a standard linked list in template format (with T being the typename) with the following relevant insertion operators:
bool PushFront (const T& t); // Insert t at front of list
bool PushBack (const T& t); // Insert t at back of list
I want to build a list of pointers to objects (we'll call them objects of class Box for simplicity) that is member data for a parent class (we'll call that class Warehouse). However, I want to have a constant Box....const Box INVISIBLE_BOX = Box(); that represents a nonexistent Box. However, I cannot use either
PushFront(&INVISIBLE_BOX)
or
PushBack(&INVISIBLE_BOX)
to add INVISIBLE_BOX to the list of boxes without getting an invalid conversion error invalid conversion from âconst warehouse::Box*â to âwarehouse:: Box*â [-fpermissive]
What can I do to make it take a constant Box? I am using g++ to compile these files.
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Sep 19, 2013
trying to understand operator overloading, and i wrote some code just to define a "-" operator to do a simple subtraction. SO, i wrote a program that can perform a subtraction between two objects and put the result in the third object. now I Just cant show the result on the console. And also can anyone define the meaning of [b1.x], like I want to know am I assigning the value to the "b1"object or the x variable? This is a very concept that I need to understand.
#include<iostream>
using namespace std;
struct Ok
{
int x;
int y;
};
Ok operator-(const Ok& a , const Ok& b)
{
Ok result;
result = (a - b);
return result;
}
int main()
[Code]...
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Apr 19, 2013
I have a list of objects that I need to read information from each object to compare to a user input prompt.
#include "Passenger.h"
#include "Reservation.h"
#include "Aircraft.h"
#include <iostream>
#include <fstream>
#include <string>
#include <list>
using namespace std;
//Function Prototypes
void flightRoster(list<Reservation>&);
[Code] ....
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Nov 12, 2014
This has been bothering me for a while now, and I finally put together an example:
#include <iostream>
#include <string>
using namespace::std;
[Code]....
In the code above, the two classes hold pointers to each other, and that's fine but it doesn't seem right since C++ prefers to pass by reference. Yes, it can still do that (see testbox and testball) but even that seems odd to me because still you need to use pointer notation for the enclosed object. Am I the only one who feels this way, and should I just get over it? Or am I missing something that would allow an object to hold a reference?
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Mar 16, 2013
will copy constructor does object initialization using another already created object? I understand that it can be applied for object initialization and not for assignment.Is it correct?
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Jul 3, 2014
I have a method to take a Tile object and make an instances of it based on some data from the original object. Than it is suppose to manipulate the a specific instance and save the results. The first loop through it works but it changes all instance as well as the base.
public static int recurse(int count, Tile[,] b,Huristic h,int check) {
if (check==1) {
boardState.Add(B)/>;
return check;
} if (check == 0)
[Code] .....
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Dec 13, 2012
#include "B.h"
class A {
public :
A()
{
s_b = new B();
b = new B();
[Code] ....
In my project i have seen static object as above . But not able to know what is the exact use of it and how they are different from general object .
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Sep 11, 2014
a function returns a temporary object like
int myfun(){
int x = 0;
return x;
}
this function will return a temporary integer now void fun1(const int & num); this function can receive from myfun().BUT void fun2(int & num); this function cannot receive from myfun() Why is that, Moreover what is lifetime of a temporary object like one returned in myfun() ???
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Mar 28, 2014
I am trying to use web api in order to return custom json response keys. For this i have return a custom class to return json response
Custom Class:
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
[Code].....
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May 4, 2013
I have a combobox with Items 1024
2048
4096
8192
String cach = form.comboCache.SelectedItem.ToString();
I am using the above code to retrive an item selected by user,But this line is giving an exception "Null Reference Exception, Object reference not set to an instance of an object"
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Mar 28, 2014
I am using session to pass object from controller to custom class in MVC Web API. here is my code, i am getting error at session.
public HttpResponseMessage Get()
{
var person = db.Persons.ToList();
[Code]....
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Aug 23, 2013
In Visual Studio 2010 C++
I have a series of existing text objects
The text properties names are
item1_lbl,
item2_lbl,
item3_lbl,
….
Based on a selection I want to change an object. I generate the name of the object I want to change in a string so from this string is there a way to get a pointer to the correct text object that is same name?
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Jan 30, 2013
I have the following map: myMap<string,vector<int>>. I now want to look through my map to see if a key exists and if it does, retrieve one of the int values from within that vector. What would be the best way to do this? Right now I have the following:
What would be the best way to look for a key and get one of the int values from its vector value? Right now I'm doing something like this:
[code]
map<string,vector<unsigned int>>::iterator it;
it = wordMap.find(someWord);
if(it == wordMap.end){
cout << "No matching entry";
} else{
// this is where I'd want to access the value (the vector) of the map
}
Is there a better way to do this?
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Sep 26, 2014
I don't have in depth code or anything. I tried this but can't seem to wrap my head around it.
Code: //header.h
namespace test {
int arr[5];
[Code] ....
Also tried putting int arr[5] in a Test class within test.h.
I have 2 structs in another file, the main, and want to make an instance of the arr variable, in a separate header, for each.
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Nov 21, 2013
How to i access setter from within a setter?
I know that getter methods can be access like
Code: getAccounts().getAccountNumber();
// for example but for setters how do i do it? this doesnt seem to work though
Code: setAccounts().setAccountNumber(accountNumber);
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Feb 19, 2013
Here is the link for my program, I want to access the average value which is located in grade.c (calculate_grade) class through driver.c (main function) but I don't know how to make "average" visible
[URL] .....
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Aug 30, 2013
I came across the below code snippet in a project and was not sure how value of variable "response" is computed. Here as we can see, pic_data holds two one dimensional arrays but "response" access both the single dimensional array as two dimensional array.
Code:
#define MAX 100
#define MAXBUF 100
u32 response;
u32 index;
}
[code]....
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Aug 3, 2013
I've been attempting to create a game with curses and I keep running into the problem of scope. I want to change or use variables of a different class in a different header file. But I don't know if I should use pointers, references or neither. Should I be programming in a manner that doesn't make it necessary to use variables outside of their class?
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