C++ :: Pointers To Automatically Null When Object Is Deleted
May 18, 2013
Say I have an object and 10 pointers to it in several other objects of varying class types. if the object gets deleted, those pointers have to be set to null. normally I would interconnect the object's class with the classes which have pointers to it so that it can notify them it is being deleted, and they can set their pointers to null. but this also has the burden that the classes must also notify the object when THEY are deleted since the object will need a pointer to them as well. That way the object doesn't call dereference a dangling pointer when it destructs and attempts to notify the others.
Auto pointers and shared pointers are not what I'm looking for - auto pointers delete their object when they destruct, and shared pointers do the same when no more shared pointers are pointing to it. What I'm looking for is a slick method for setting all pointers to an object to null when the object destructs.
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Apr 13, 2014
I'm using Visual C++ 2010 and SFML game library. I want to know how to move an object from right to left automatically and back left to right??
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Oct 15, 2014
For some reason I keep getting null pointers in most of my functions, and in my convertTime function the numbers are way higher than they should be.
Code:
//Utils.H header file----------------------------------------------
//This function takes the radius of a circle and returns the diameter, the circumference and the area.
int circleStatistics(double radius, double *diameter, double *circumference, double *area);
//This function takes a number of days and returns how many years, weeks and remaining days that is.
int convertTime(int days, int *y, int *w, int *d);
//This function takes a length of time and calculates the dilation of that time at a percentage of the speed of light.
int lorentzTimeDilation(double normalTime, double percentC, double *dilatedTime);
[Code] ....
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Dec 2, 2011
Code:
public class ColorGenetics
{
public static hk1Class jw;
public static linkedClass link;
}
[code]...
Code builds fine but compiler says I tried to use bject link w/o providing an instance. Class linkedClass has an instance of Class hk1Class set to var jw1.I had linkedClass useing the same var jw for the object instance. I changed it to jw1 thinking that would clear it up and it didn't.
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Nov 18, 2013
I have built LOG4CXX lib and DLL and trying to use it in my application
Loh.h
class Log
{
public:
[Code].....
In my main I am initializing Log class object and calling Debug method to log debug message to a file.
Issue I am facing is at if(CLogger::oLogger != NULL) which is always returning oLogger as NULL.
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Feb 14, 2013
lets say I have a pointer p_unit of type c_unit* (c_unit is an a.b.c.)
I have a function that returns a pointer to a new c_unit object:
c_unit * man_add_unit() {
c_unit * local_p_unit;
unsigned short int local_run_code;
print_man_add_menu();
local_run_code = get_a_run_code(); // this bit just gets user input
switch (local_run_code)
[code]....
I assign that to p_unit, then add it to a vector v_units:
p_unit = man_add_unit();
v_units.push_back(p_unit);
cout << "New unit added.
";
The whole program runs on a loop, and another thing the user can do is to print out data on c_unit objects pointed to by v_units. The problem is, in that function up there ^ I give the user the option to go back to main menu without creating a unit.
Since "local_p_unit" is declared but not assigned an initial value, I'm guessing the function would return a "null" pointer (which is what's hanging me up). If I just let this run with the above code, and go to print out the unit data, the program crashes.
I tried to make an if thing with p_unit == 0 but this always returns false and doesn't catch the "bad" unit that will subsequently cause a crash.
Btw, I have considered assigning a reference to a generic c_unit object to that there local_p_unit so it won't return null, then remove pointers to that object from v_units at the end of the loop.. But I know there's got to be a better way.
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Apr 12, 2013
[URL] ....
Which object's draw is being called?
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Sep 4, 2014
Lets say for example I have the following vector:
vector<Component*> mComponents;
and a function print() inside of class Component that prints the objects name.
How do I loop/iterate through the vector to access the print function in each object.
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Apr 8, 2013
Is there a point in dynamically creating a pointer during runtime only to dereference it? (if that is the right term, as in *pointer, depoint it?)
In this case should I perhaps store pointers instead of references?
Inventory.cpp
Code:
bool Inventory::addItem(InventoryItem& item) {
addItemAmount(item);
if (item.getAmount() > 0) {
if (hasEmptySlot()) {
addNewItem(*item.clone());
return true;
[Code] ....
Also I was wondering, is there some sort of built-in cloning functionality or do I have to write the clone functions myself? When creating new instances I see that I can either pass the constructor properties or a reference to an object of the same type.
For instance:
Code:
new InventoryItem(index, name....);
new InventoryItem(const InventoryItem&);
Is the second one casting?
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Nov 11, 2013
Is there any way to set a "lock" on certain couts from system ("cls"). You can this with const to "lock" a variable to a certain value so I am wondering if that is true for couts from system ("cls"). This would make my program much simpler to write.
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Feb 18, 2014
I am looking at one of the functions of an exercise:
void escape(char * s, char * t) {
int i, j;
i = j = 0;
while ( t[i] ) {
/* Translate the special character, if we have one */
switch( t[i] ) {
[code]...
Notice the while loop evaluates the current value in t to true or false. When we hit the null terminator, does that get evaluated as 0 and hence evaluates as a falsy value so the while loop exits?
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Feb 20, 2015
Been away from c++ for a few months now (apart from answering a few questions on this site). I was trying to see if I could do a simple program using just my memory that involved unique_ptr's, but getting an error:
"attempting to reference a deleted function". I thought that by getting a reference to my pointer would not invoke a copy constructor but i'm clearly wrong.
Here's the code:
#include <iostream>
#include <memory>
#include <vector>
class Shape {
public:
virtual void Draw() = 0;
[Code] ....
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Oct 31, 2013
I have a small questions in the behavior of Structure, I have declare a structure with 10 components. Some of the components in the structure has already their value but when I use
The structure components in a function DLL function those value I set previously has been deleted or empty. I don't know what is the problem...
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Jul 4, 2013
I have two questions about C programming here :
1. I want to make a file in the program directory that can't be deleted by user out of the program make that file.for example if I make a file named "123.xyz" by the program named "text.exe" and then exit test.exe ,if I tried to delete the file 123.xyz I faced the error and I could not do it but by the test.exe program that make that file.
2. I heard about a function called "Parbegin()".any way i want to know is there any possible way to run two or more functions of a file.c together,like the parbegin function did an do in OS?
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Oct 26, 2014
i tried running my code and i keep getting the error "call to implicitly-deleted default constructor of 'node'. My code is as follows
//.h file
typedef struct node * point
struct node{
string data;
node *next
}
[code]....
I get the error at the line "ptr1 = new node;" I tried putting a default constructor for my node struct and that fixed the problem but a new problem arises. It states that i have a linker error after i compile it with a default constructor.
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Mar 31, 2015
When you login to my site my loginservice which is done by ajax and json make a session called context.Session["Name"]. With BreakPoints it shows that everything is good and the variables are in place. However when I use Session["Name"] it comes out as null.
I will add my code at the bottem not
using System;
using System.Collections.Generic;
using System.Linq;
[Code].....
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Dec 9, 2014
I am trying to execute a very simple piece of code. But I am unable to find how the value of T[i][j] is changing all of a sudden. CODE:-
insert Code:
void initialize(float** &T,int NP,int D,int low,int high) {
int i = 0,j = 0;
T = (float **)malloc(NP*sizeof(float));
for(i = 0;i<NP;i++)
[code].......
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Feb 13, 2015
I am wondering if integers and unsigned integers automatically assigned to zero (0) upon declaration like so:
bool randomFunction() {
int i;
if (i == 0) {
return true; //Will most modern compilers return true here?
} else {
return false;
}
}
I am just curious as I have always initialized my ints/unsigned ints variables. Would save me a lot of typing if I didn't have to do this all of the time.
I know that floats and doubles you still have to initialize.
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Sep 17, 2012
Im doing a little game, casting dices etc. The problem is that the program will ask for player 1 then if i enter a name and enter it will ask for player two and so going on until i just press enter with a empty field and then continue the game.
The problem is i don't have any clue what code bits to start studying and how i shall lay it up, feels like i need a new string declaration automatically for each name.
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Mar 8, 2013
I have a triple hierarchy class:
template<class T> class Singleton;
class Base;
class Sub : public Base, public Singleton<Sub>;
I' using underlying auto pointers, that's why Singleton is a template class and Sub passes itself as a template parameter. I'm developing Singleton and Base and a public API allows anyone to add their own sub classes. I actually want a real triple hierarchy like this:
template<class T> class Singleton;
class Base : public Singleton<Base>;
class Sub : public Base;
So that external developers don't have to worry about templates and complexity. The problem with this is that my implementation in Singleton will now call the constructor of Base whenever I create an instance of Sub (since the template parameter is Base).I was wondering if this could be done by pre-processor macros:
template<class T> class Singleton;
class Base : public Singleton<__CLASS_NAME__>;
class Sub : public Base;
Where __CLASS_NAME__ is the class name that will be replaced by the pre-processor. Theoretically this should be possible, since the __PRETTY_ FUNCTION__ macro actually returns the class name. The problem is that one cannot do string-manipulation to remove the function name from __PRETTY_FUNCTION__.
how I can accomplish this so that the Sub class is not aware of inheriting from a Singleton<template> class?
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May 7, 2013
When using wxWidgets, i am tempted to deallocate memory using delete in the destructor, but my program crashes on closing. I try to do something like this:
class mainwnd:public wxFrame{
public:
mainwnd():wxFrame(NULL,wxID_ANY,wxT("test")){
menubar=new wxMenuBar;
[Code] .....
tell me why? and is it done automatically?
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Mar 26, 2012
How do I tell c++ to move the mouse in place x?
for example, I run a c++ program and the mouse moves to the top left corner of my screen.
How do I go about doing something like that?
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Nov 15, 2013
I am new to programming all together but i have been writing a program in c++ and im coming up against an issue with my array.
#include<iostream>
#include<iomanip>
#include<string>
using namespace
int main () {
int a ;
int b ;
char answer ('Y') ;
[Code] ....
I am trying to get the program to increase say year one by 1 when the condition is met i have tried
if ( a >= 70 && a <= 100 && b == 1)
{grade [0][0] = 0 + 1;}
and
for (grade[0][0] = 0 ; a >= 70 && a <= 100 && b == 1 ; grade [0][0]++)
{grade [0][0]= 0 + 1 ;}
Now all that i want is that the array will take the information from int a and int b and then add 1 to the appropriate part of the array . I have tried putting it in deferent places but its not working for ether. the program will run but it will not add to the array.
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Jul 7, 2014
I recently noticed that I don't need to include the required header files inside header files that I have written myself. As as example, GLuint is defined using typedef unsigned int GLuint; inside glew.h. If I create a sample.hpp header file and mention GLuint without including glew.h, the compiler automatically works out that there is a typedef in glew.h. However, if I mention GLuint in a source file the compiler starts to complain. I have seen this happen in VS 2010 and 2013.
Edit: I should have mentioned that I am not including any other header files so I'm not indirectly including glew.h
In case you need to look at the code:
#ifndef CP_SHADER_LOADER_H
#define CP_SHADER_LOADER_H
namespace cp {
[Code].....
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Dec 15, 2013
If we have to arrange large array structure, and we should also have to set a field which is the 'index' of elements in the structure array as:
typedef struct {
int index;
char [MENU_ELEMENTS_CHAR_MAX];
int value;
boolean enable;
} stc_MenuEntry;
const stc_MenuEntry GlobMenu[] =
[Code] ....
Suppose we have a lot of row like those written before: also many structured array , and we should mantain: inserting and deleting elements, without having to worry about index error insertion, what kind of preprocess should we choose to best perform the automatic field writing? Obviously we could set properly any array field as:
{
{START_INDEX, "menu_voice01",100, TRUE },
{NEXT_INDEX, "menu_voice02",100, TRUE },
{NEXT_INDEX, "menu_voice03",100, TRUE }
......
.....
};
Just to make the task easier, maybe to allow a 'program filter' to find and subtitute the field as required.
We should also put theese menu variable in RAM, and perform the field init, setting the index at run time, but if we want to save RAM (const attribute chosen) we must find a solution.
I thought about UNIX/LINUX OS filter like sed and awk which would maybe perform the task, before giving the source file to the building process, but I'm working on Windows environment and I don't know the appropriate tool to do this kind of work.
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Jul 8, 2013
In my program, I create controls by deriving base objects of them I've made. These controls are then are attached within the OnCreate() function via a method I've created. For example:
Code:
class tChat: public TextBox {
public:
void OnKeyDown(UINT &KeyCode) {
if (KeyCode == VK_RETURN) {
MessageBox(NULL, "Pressed enter!", NULL, 0);
[Code] ....
The use of AddControl() feels quite redundant and is only their to parse a pointer to txtChat's Parent. I'm trying to see if it's possible to remove this line and automatically associate txtChat to fMain.
Currently my hierarchy looks like:
[User's derived Form] -> [MDIForm or Form] -> [FormBase] -> [Object]
[User's derived Control] -> [TextBox, etc..] -> [Control] -> [Object]
The user can then derive the Form and Controls and use their virtual OnEVENT functions to handle all the messages they expose.
So far my first concept is using the order-of-creation based on base-class constructor's being fired to determine which object is associated with what.
If I create a copy of a class (i.e. a Form-derived object), first the Form's constructor is fired, and then the constructor's of any class-based member-variables are fired. Is this a safe assumption? I imagine the only time this could be affected is by another thread creating the object of a Form or Control derivative?
If this assumption is true, I could save the 'this' pointer from the FormBase constructor, and then associate it with each Control via the base Control class' constructor? Then to ensure thread-safety, I could map the current FormBase pointer to the local thread id to ensure no conflict if multiply threads are creating forms at the same time?
I've created some mock-up code before trying to implement this into my main code. The following keeps track of the current Form being created by using a ThreadId-based map. When a control is created it gets the FormBase pointer based of it's ThreadId calling. The control then calls an Attach() function of it's parent Form using the pointer it just got, and parses a pointer to the control. The Form then adds the control's pointer to a list. When the Form eventually parses WM_CREATE, it automatically pulls the controls from the list and fires their virtual Create() functions to build them.
Mock-up:
Code:
#include <Windows.h>
#include <string>
#include <map>
#include <list>
class FormBase;// Forward declaration
class FormMap;// Forward declaration
class Object {};// Base Object
[Code] ....
Is this plausible to use? I imagine C++ does not have many "guarantees" about how it creates objects and when. But I thought it would be safe that it would never create member-variables before the class of them is first created?
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