C++ :: Singleton Pattern - Delete Pointer Twice
Feb 22, 2012
environment : qt creator 4.7
code:
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
using namespace std;
class singleTon {
[Code] ....
this is a singleton pattern first,it doesn't matter, why I could delete this pointer twice?because the gcc compiler?That mean in the surface, "delete pInstance1;" this movement just mark the memory pInstance1 has been deleted but not real?does any one encounter this phenomenon?
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Jan 17, 2013
I have the following code where I use the singleton design pattern, but I get the warning:
warning C4715: 'CM::Instance' : not all control paths return a value
Code:
CM& CM::Instance() {
DWORD dwWaitResult = WaitForSingleObject(mutex, INFINITE);
switch(dwWaitResult) {
case WAIT_OBJECT_0:
[Code] ....
How can I fix this warning?
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Jul 9, 2014
I was going through Singleton design pattern and get to know that objects can be created only by static function of that class and constructors are make private.
My question is, why assignment operators are not made private through which we can create a copy of already existing object.
I tried below code and assignment works, so I have new object sc3. I know that its referring to memory of sc1 but finally I was able to create object without using static function.
Also, why copy constructor not made as private.
Below is code:
#include <iostream>
using namespace std;
class Singleton {
private:
static bool instanceFlag;
[Code] .....
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Jun 26, 2014
I have a class in my application that only needs to be created once, but the object needs to be available to all other classes in my application if necessary. Since declaring everything static can be restrictive (as I understand), I created a class like this:
class Foo {
// Data members
// Constructor/Destructor
// Functions
};
extern Foo* myFoo = new Foo();
And then the global variable gets deleted at the very end of the main method when everything is done:
#include "Foo.cpp" // (yes, I know this is normally bad, this is how I'm required to code)
int main() {
// do stuff
delete myFoo;
return 0;
}
These won't link, though, because I get undefined reference linking errors to myFoo wherever I use it. I'm pretty sure this means I'm creating a singleton wrong, but I'm not sure what I'm doing wrong -- there's no const conflicts and the pointer is properly initialized (to my understanding). If there's a better way to do this than extern, I'm completely open to it, as long as it's understandable and works.
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May 24, 2014
All the undos and redos were working fine until the pointer data members came into the picture. The problem is that the values pointed to changed, but the pointers themselves did not. So restoring gives the same pointers but they still point to the new values. I think the solution is that the classes that are the pointer data members themselves need their own Mementos (which would be a lot of work because there are many data member pointers in my program). Is that the only approach?
Here is a sample code to show what I'm talking about. You can compile and run the program to see the problem it has restoring values of pointer data members:
#include <iostream>
#include <string>
#include <memory>
#include <vector>
#include <list>
#include <cstdlib>
#include <ctime>
class FoodHistory {
[Code] ....
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Jan 4, 2015
void myfuncion(){
int *a = new int[10];
int b[10];
int *p = b;
delete a
delete p
}
I cant delete b and/or p but how can i check it if i can use delete or not?
i want to check if the pointer is pointing on function temp variable ( those what gets deleted after function ends .
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Sep 2, 2014
int * ptr = new int[5];
p += 2; //p now stores address of 3rd element in array
delete [] p;
what will be deleted??? all 5 elements or just 3rd, 4th and 5th elements of array(in result making a memory leak)
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Apr 15, 2013
let's say I have class LinkedList:
class LinkedList
{
public:
class Node
[Code]....
Do delete newL:
1) (*newL).~LinkedList
2) delete newL
3) delete[] newL
4) none of the above ;)
If the answer is 4, what should I do?
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Aug 7, 2014
In jumping into C++ it says something like this: It's not necessary but when you delete a pointer it's a good idea to reset it as a null pointer. That if your code try's to dereference the pointer after being freed, your program will crash. This happens to a lot of experienced programmers.
This could corrupt users data. delete p_int;
p_int = NULL;
1. If you can deference a pointer after the memory is freed, why can't you just delete the pointer?
2. If you can do 1, how do you delete the pointer using code?
3. Every thing I've read says that free memory is handed out in a sequenced order. I don't believe that is true at all. I may be wrong. Why can't you put the data in any number of places if it will fit. Isn't the compiler smart enough to know where bytes (bits)and pieces are stored?
4. If you storing anything in free memory must use a pointer to it?
5. Can a pointer or something similar be used with stack memory?
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Jul 29, 2013
I'm tying to create a program that evaluates all possible actions for a certain problem.
So what i'm basically trying to do is to create a sequence of actions, evaluate them to check if it's the best sequence, change the sequence, evaluate again and so on until all possible scenarios are exhausted, leaving the best one in the end.
My approach to this at first was to create a tree of all possible options and then evaluate each branch. Since there are a lot of possible cases i ran out of memory while the program was still creating the tree. I changed this to create just a branch, evaluate it and then modify it.
I was still getting memory problems. I declared a class tNode and declared a vector<tNode*> branch. Then i created all the nodes i needed for that branch with branch.push_back( new tNode() ). When i wanted to modify the branch i simply used branch.pop_back() and again a branch.push_back( new tNode() ). I figured i was getting the problem because although i clear the vector, i don't actually clear the reference in memory. Is this correct? If so, how can i actually delete the memory space and not just the pointer in the vector?
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Apr 17, 2013
I have following:
struct Point {int* a; int b;};
vector<vector<Point> > numbers;
vector<int> example;
The numbers vector has a matrix of a sort and each of the members are pointing to one member in the example vector. A member numbers.at(2).at(3).a is pointing at example.at(3). Now, can I remotely delete a member in the example vector using the pointers? Like so:
delete (*(numbers.at(2).at(3).a));
I know there is a more convenient way to delete members, but this is a very specific case I'm working on.
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Dec 3, 2013
I have little problem which causing memory leaks.
Parent > Multiple Child(Parent parent) > Child destructor deleting parent => next Child destructor crash
Example code: without using:
class Parent {
public:
Parent() {
for(int i = 0; i < x; ++i) {
for(int j = 0; j < y; ++j)
childs[i][j] = new Child(this);
[Code] ....
If you read code, on Parent destructor i = 0 & j = 1 its going crash.
Parent will be deleted aswell, but it give me assert: _block_type_is_valid(phead- nblockuse)
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Feb 25, 2015
An attempt to create a class which is basically a mimic of vector<int> i don't seem to know how to delete pointer x in a destructor to free memory, also on pushback and pushfront methods, i can't free y when i implement delete[] y; y=NULL; i get some NULL out put when cout 'ing the object in main, why is that happening and how do i free memory y.
#include<iostream>
using namespace std;
class vectorOfint{
int* x;
int size;
public:
vectorOfint();
[Code] .....
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Dec 22, 2012
Goal: To allocate some memory as a char*, read in some binary data, re-interpret it as a float* and then free the memory.
My code looks like:
void someFunction(float* &result) {
char * tmp = new char[1000];
//...Fill the char buffer here...
result = (float*)tmp; //Reinterpret binary data as floats
[Code] ....
Is the cast back to char* necessary on the red line (or could I have validly left it as float*)? Would it be different if I had written char * tmp = (char*)malloc(sizeof(char)*1000); on the blue line (and correspondingly used free (char*)floatData on the red line?
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Oct 25, 2014
Code:
class BoundingBoxTest : public DemoApplication {
public:
#ifdef DYNAMIC_CHARACTER_CONTROLLER
btCharacterControllerInterface* m_character;
[Code] ....
I am creating the object by calling : BoundingBoxTest::Create();
Do I make a getter to retrieve the demo object or do I build on the Create() method... So that it will return the instance if it is not null. and creates one if there is none?
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Apr 6, 2013
I need to implement a singleton, so I've been reading about it online and I'm still not quite sure about all the types of constructors I need to declare:
Code:
class my_singleton {
private:
my_singleton();
my_singleton(my_singleton & X);
my_singleton(const my_singleton & X);
[Code] ....
Is this OK?
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Oct 6, 2013
I've tried to program a Singleton class. But the problem is that I don't know how to access the g_pInstance() function. Because this is not working because the constructor and deconstructor is private:
Singleton::g_pInstance()
Code: #include <iostream>
using namespace std;
class Singleton
{
[Code]....
I'm not sure of how to access any object, function, variables in the class when you are using a Singleton. How do you access that?
I'm just asking because I want to know how to do that if I have to use a Singleton sometime when I'm programming.
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Aug 24, 2014
I have code like this:
Code:
if (S::I().File.isDirectory(arg, S::I().Stat.workingPath)) {
// find out if there is -r option after 1st argument to join files
src_temp.join = true;
S::I().Stat.getRegEx = true;
}
The S is singleton class and I() returns instance of Singleton; there is a Stat object too. When I debug (line by line) I would like to see what values are in the Stat object. Is it possible to do it using Watch panel in Visual Studio 2010?
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May 28, 2012
I've been upkeeping a mess of a code recently, that uses "pseudo" singletons. Basically, the current code has "Initialize_All" static functions that initializes all the singletons in a given order. At the end of the program, we call "Destroy_All", and destroy everything in the reverse order.
The code is actually heavilly dll'ed, and Initilize_All and Destory_All are referenced counted. We ask that any client who uses our code call Initialize_All first and then Destroy_All when they are finished. The first Initilize_All will initialize everything, and the last Destory_All will delete everything.
This is showing its limits.
I'd like to move us to a fully singleton design. The singleton pattern means we don't have to use an Initilize_All, and each singleton can manage construction dependencies by itself (we are mono-threaded).
Each singleton is "clean", so it is cleans itself up at dll destruction.
The big question is this one:
If there is a singleton dependency during destruction, eg: ~A requires an instance of singleton B (which is in another DLL), are we guaranteed proper behavior?
Or, is there an "Static de-initialization order fiasco"?
If yes, are there any design that can combat this fiasco, short of having each singleton register itself in a manager, that will destroy them in reverse order?
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Oct 11, 2014
My current idea of how to work with user settings goes like this:
1. Create a class to hold all of the user settings.
2. Use that class to load/save/hold settings in memory.
3. Create an instance of that class once in the entry point of the program (int Main or whatever).
4. Pass, by reference this same class instance around to all of the other classes that need the user settings.
5. Once all other objects deleted, save and then delete the User Settings class.
I created a psuedo-code example below of this. My question is if this is the best way or should I be doing something else. In particular, I am wondering if somehow I can avoid passing the settings class by reference all of the time. Would this be a good case scenario for a "Singleton" type class?
#include <string>
class UserSettings {
private:
std::string SettingOne;
int SettingTwo;
bool SettingThree:
[Code] ....
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Feb 3, 2014
#include <iostream>
int main() {
int bit = 1;
int init = 0xf ^ (1 << bit);
char* c = new char(2);
sprintf(c, "%x", init);
std::string initVal = std::string("4'h") + c;
std::cout << initVal << std::endl;
}
Above code is compiling as I expect it to be.
Problem is when I run it, it prompts me the following message:
Out-of-bounds access (ARRAY_VS_SINGLETON). Passing "c" to function "operator +(HSTString const &, char const *)" which uses it as an array. This might corrupt or misinterpret adjacent memory locations.
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Dec 9, 2014
I have to manage a Clinic. I need to delete a booking (for example, if John said he's coming on March 22nd at 15:30 but then he say he's not going to come, I have to delete that booking so another person can use it).
idSearched: the id of the person that is not going to come. I have a lot of specialties and each one has a list. So I ask for the speciality to delete the node (the node contains John's booking). If I don't find it, I return (-1). searchSpecByID return a pointer to the list where the speciality is. So head will point to the first node of the list. In nodeToDelete I have the node I want to delete.
The program detects OK when is the first in the list and when not, but it doesn't delete the node.
Code:
typedef struct bookingList{
tSpecialty specialty;
struct nodo* intro;
} tList;
[Code].....
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Jul 13, 2014
#include <map>
#include <iostream>
#include <stdexcept>
[Code]....
SuperSmartPointer<int> ptr4((int*)ch); this line gives error error as double deletion will occur.
Solution :
1) make the reference map global variable.
2) wrap the map in a non-template singleton class.
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Aug 20, 2014
I'm playing with the idea of a singleton base class, but I'm having an issue with how to implement the GetInstance() function in the base class. Since I'm trying to make this ridiculously simple for the child, I'd like to handle that in the base.
class Singleton {
private:
static Singleton* instance;
Singleton() { Construct(); } // Private to avoid other instances
[Code] .....
It would be easy to use like so:
class Hello : public Singleton {
private:
std::string hello;
void Construct() { hello = "hello"; }
public:
std::string GetHello() const { return hello; }
};
Then the instance would be handled like so:
std::cout << Hello::GetInstance()->GetHello();
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Jul 18, 2013
I am trying out a technique for a singleton class:
// access controlled singleton, accessed through function "instance()"
// singleton is constructed in this function
// so that constructor and destructor will be used
class single {
// private constructor/destructor
[Code] .....
Playing around with the code in main(), I am having trouble with auto:
single& s = single::instance(); // works fine
auto a = single::instance(); // error ~single() is private
When I make the destructor public, the output of the program is:
ctor
dtor
dtor
So I fixed this by typing auto&. I'm still confused though, why wouldn't auto know I am returning a reference?
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Jul 4, 2014
I've been working on this code that should be looking like
1 3 5 3 1
3 5 7 5 3
5 7 9 7 5
3 5 7 5 3
1 3 5 3 1
but mine appears like this
1 3 5 3 1
3 5 7 5 3
5 7 9 7 5
3 3 5 7 9
1 3 1 3 5
This is the code I've got for now, I just don't know which logic I need to fix
int main(){
int r;
cout << "Rows?" << endl;
cin >> r;
for (int i = 1; i <= r; i+=2){
for (int j = i; j <= r+i; j+=2){
cout << j<< " ";
} for (int k = i+2; k >= i-1; k-=2){
[code]....
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