C/C++ :: Make Class That Can Only Have One Object Of It Created?
Oct 7, 2014
make a class that you can make only one Object of it.
For example if you have Class A.
Let's say you create one object A* a=new A();
Now the next time you, try to create another object. For example:
A* b=new A(); What will happen is that b will get the same object (or reference) as a. In other words hey'll be pointing towards the same place. So basically you'll only have one object of it created. I tried doing it but I couldn't quite make it.
Here is what I tried: (but couldn't complete the exercise)
class God
{
public:
static int num;
static God* god;
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?
I'm currently creating a text-based RPG, to get myself back into learning C++ again. The problem seems to be with the if-else ladder of statements, the user selects which race they wish to play as, which as a result creates the appropriate object for that race.
This is the character selection option code:
std::cout << "Please select a race: Human [1], Elf [2], Dwarf [3] or Orc [4] "; std::cout << "Race selection: "; std::cin >> race_selection; std::cin.ignore(); switch (race_selection) {
[Code] .....
The problem here is, regardless of which race I use using the above switch statement, the Human object always seems to be created, instead of the object for the desired race.
I am to first increment data members of object that has not created dynamically (i have done with this part),now i have created object dynamically and how to increment its data which i have passed as argument as:
m_vRenderObjects.push_back(new Objects(mOperatorMesh)); /// this is never called ~Objects(void) { OutputDebugStringA("Cleanup Objects "); if (StateMachine != NULL)
What c++ code can be used to make an 'X' move through a maze. I have some code, but I'm not sure where to go from there. I have divided the program into three files, A header file, a main file and a .cpp implementation file.
In my implementation file I have:
#include "Maze.h" Maze::Maze() { } void Maze::mazeTraversal(char maze[][COLS], int row, int col, int direction) { enum Direction {DOWN, RIGHT, UP, LEFT}; switch(option)
I've got a calendar in Form 1 in my code, and buttons in Form2. I need these buttons to send codes for this calendar in Form1. How may I make these work? My friend told me to do a function as a new class, but I'm not sure how can I do this.
#include <iostream> #include "curve1.h" #include "curve2.h" using namespace std; int main() { Curve1 curve1Obj; Curve2 curve2Obj;
[Code]...
Base class Score has two derived classes Curve1 and Curve2. There are two curve() functions, one is in Curve1 and other in Curve2 classes. getSize() returns the value of iSize.
My base class header score.h looks like this:
#ifndef SCORE_H #define SCORE_H class Score { private: int *ipScore; float fAverage; int iSize;
[Code]...
You can see that I have used curve1Obj to enter scores, calculate average and output. So if I call getSize() function with cuve1Obj, it gives the right size that I took from user in enterScores() function. Also the result is same if I call getSize() in score.cpp definition file in any of the functions (obviously). .....
The problem is when I call curve() function of Curve2 class in main (line 23) with the object curve2Obj, it creates a new set of ipScore, fAverage and iSize (i think?) with garbage values. So when I call getSize() in curve() definition in curve2.cpp, it outputs the garbage. .....
How can I cause it to return the old values that are set in curve1.cpp?
Here is my curve2.cpp
#include <iostream> #include "curve2.h" using namespace std; void Curve2::curve() { cout << "getSize() returns: " << getSize() << endl; // out comes the garbage }
Can I use a function to simply put values from old to new variables? If yes then how?
I am writing a program which is using SDL library. I have two different classes which one of them is Timer Class and the other is EventHandling Class.
I need to use some member functions and variables of Timer in some Eventhandling Class member functions, Although I want to define an object of Timer in int main {} and relate it to its member function that has been used in Eventhandling member function in order that it becomes easier to handle it, I mean that I want to have for example two objects of timer and two objects of Eventhandling class for two different users.
I do not know how to relate an object of a class from int main{} to its member function which is being used in another class member function.
how to structure my classes so that they all "wire together" and inherit the proper functions and data that I want them to. I want to have a Car.c and car.h which are "wired" with body.c/body.h, which in turn is wired with a frame.c/frame.h, wheel.c/wheel.h, and driver.c/driver.h.
Each part of the car holds some type of data, mostly ints: The car has a (total) mass and car_name. The body has a mass and color. The frame has a mass. The wheel(s) have a mass and force. [There will be 4 instances of wheel] The driver has a mass and driver_name. Each of these functionalities must come from their respective .c and .h files, and be amalgamated in the car.c and car.h (which should contain all the functionality of its parts). Then, in my main test program, I am to make an instance of car and hardcode in its values of: mass (which comes from the total mass of all of its parts, this is where i start to lose it.
How will I access its parts' masses in the test program?), color (a character array), current position (an integer), current velocity (an integer), and current acceleration (which comes from the total newton force of the 4 wheels, again this is where I start to get very confused). (Then in the test program I am to print out a simulation of this car over a period of 100 seconds, and show its position, velocity, and acceleration at each point (based on the mass, total newton force, and starting position). This part is of course a simple while loop, and is somewhat trivial.)
From what I understand, I will need to allocate memory for all of the data each class holds. Then, using function pointers, as well as #include "X.h" , I will need to somehow link up all of the classes together so that car has access to all of the parts' functions which set, for example, the newton force of each wheel.
We have learned a slight bit about structs, malloc, sizeof, and pointers, but I have not used them to link functionality or data from separate classes together.
I want to make an object, which moves from x1,y1 to x2,y2 in a straight line, also make a sinus over the line (so the x,0 is the line itself, and cux,cury is the object. So the object will move as a sinus over the line. How do I do this in c++?
I have a class MySeqBuildBlockModule that I am inheriting from: public SeqBuildBlock. Other than constructor and destructor, this class MySeqBuildBlockModule has a method: prep.
class MySeqBuildBlockModule: public SeqBuildBlock { friend class SeqBuildBlockIRns; public: MySeqBuildBlockModule (SBBList* pSBBList0, long TI1_In, long TI2_In)// more arguements in this constructor of derived class : SeqBuildBlock (pSBBList0)
[code]....
I would have like to intiantiate an object "myIRns_3" of a class defined in third party library
SeqBuildBlockIRns myIRns_3(pSBBList2);
and would like to access it from the prep function as:
I tried to instantiate following in either private section or in constructor; but w/o any success:
SeqBuildBlockIRns myIRns_3(pSBBList2);
ERRORS encountered:
When I tried to do it inside the constructor, I get the following errors:
MySBBModule.h(113) : error C2065: 'myIRns_3' : undeclared identifier MySBBModule.h(113) : error C2228: left of '.getEnergyPerRequest' must have class/struct/union type MySBBModule.h(116) : error C2065: 'pSBBList' : undeclared identifier MySBBModule.h(116) : error C2227: left of '->prepSBBAll' must point to class/struct/union
When I tried to do it in private section, I get the following errors:
MySBBModule.h(106) : error C2061: syntax error : identifier 'pSBBList2' MySBBModule.h(113) : error C2228: left of '.getEnergyPerRequest' must have class/struct/union type MySBBModule.h(116) : error C2065: 'pSBBList' : undeclared identifier MySBBModule.h(116) : error C2227: left of '->prepSBBAll' must point to class/struct/union
Information: I'm using Code::Blocks v12.11. (I'm using C++/SDL2, but I think that's of no relevance)
Problem: I create a class named "CSprite" in a "Sprite.hpp"-file. I create a "Sprite.cpp"-file, which includes the "Sprite.hpp"-file. I define the methods of the class "CSprite" in the "Sprite.cpp"-file.
When I try to create an object of "CSprite" in the class named "CPlayer" in the file "Player.hpp" I get an error message. (<-- Looks complicated I know, the code example will be more usefull than this)
Error in the build messages: C:UsersLinoDocuments1 Data LinoFreizeit1 ProgrammierenC++ & SDL2The Running ManCPlayer.h|30|error: 'CSprite' does not name a type| ||=== Build finished: 1 errors, 0 warnings (0 minutes, 1 seconds) ===|
Code Example:
Sprite.hpp #ifndef _SPRITE_HPP_ #define _SPRITE_HPP_ class CSprite {
[Code] .....
What did I miss? Did I include the wrong file? Or did I Forget to include the file? Why do I get the error message?
I also tried it with a pointer declaration and the "->" Operator but I got the same error message. I know I could just write a new function to load the texture in my "CPlayer"-class but this would not really answer my question.
I fully understand that a variable of one simple data type cannot be assigned to another of a different data type in an assignment statement, except when type-conversion(i.e. casting) is employed. For structured data types (like classes), I know that the assignment operator can be overloaded; but this only addresses objects of the same type.
My problem is that I have read data from an input file into an object of one class, but I want to transfer the contents into an object of a different class in an assignment statement. Can this be realized given that the two operands of the assignment operator (=), in this case, would be of two different types?
I have two classes one called Date and the other is University , Date class has two overloaded operators , ostream and istream to take in the data and print them out :
The University class has an object of type Date called establishDate and I must use this to print out the date along with the University name and location, here's University class :
University.h
class University { public: University (); // constructor friend ostream & operator<<(ostream & out, University & x); // print the university data friend istream & operator>>(istream & in, University & x); // to read university data
I can't seem to make the STL iterator class work how I need it to.I am implementing a multi list graph and I need to iterate through my STL list of Vertex pointer objects. I keep getting the error:
Error 1 error C2679: binary '=' : no operator found which takes a right-hand operand of type 'std::_List_iterator<_Mylist>' (or there is no acceptable conversion) and the same for != for my terminating condition.
template <typename V, typename E> void Graph<V, E>::InsertEdge(V from, V to, E edge) { list<Vertex<V>*>::iterator iter; for(iter = m_Vertices.begin(); iter != m_Vertices.end(); ++iter)
Well, sort of - my question is, since the destructor has to be virtual in order to be marked final (you get an error otherwise), does this cause virtual function overhead anywhere, or add a vtable?
