C++ :: Cloning Object - Store Pointers Instead Of References?

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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C++ :: Cloning Object Passed By Function?

May 21, 2014

Is it correct for me to make a clone of testobj in function AddTest below, before i add it to my map? What i want is an user pass testobj to me though AddTest, and after i add it into my map, i do not want to have anything to do with the original testobj anymore. I.e, they are two copies, one belong to Device, one belong to the caller, both has no link to each other.

Also regarding the GetTest method, i prefer to return a raw pointer, as i do not want to force the caller to use smart pointer. And i also do not want the caller to be able to do anything that may change testobj in the map. So i am not sure to return as const reference or make a clone of testobj on the map and return it to the user (but caller need to delete the testobj when it is not used).

Code:

class Device {
public:
void AddTest(const Test* const testobj) {
_pTest.insert("ss", QSharedPointer<Test>(test->clone()));
} const Test* const GetTest(QString str) {
return _pTest[str].data();

[code].....

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C++ :: How To Hold Pointers / References To Abstract Class

Nov 15, 2014

I have an abstract class named Terrain, and a class named RoadMap, which supposed to hold an N*N array of Terrains. But I'm not sure what type should the RoadMap class hold:

Code:
#ifndef TERRAIN_H
#define TERRAIN_H
class Terrain {

[Code] ....

I can't use an array of refernces here, so I tried this:

Code: Terrain** terrain; and then I thought this was the way to go:

Code: Terrain (*terrain)[]; But now I'm not sure.

The N*N matrix size supposed to be determined according to a given input... What type should I use there?

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C++ :: How To Store The Same Instance Of One Object In Multiple Vectors

Feb 4, 2015

If I have a class object and multiple vectors, how do I make sure I store the same instance of that object in both vectors? For instance:

Object object;
std::vector<Object> vectorOne;
std::vector<Object> vectorTwo;
vectorOne.push_back(object);
vectorTwo.push_back(object);

Are the objects in both vectors the same instance of the object? Like if I called vectorOne[0].setValue(somethingDifferent); would the value be changed for the object in both vectorOne and vectorTwo? If not, how do I make sure that I only have one instance of the object I'm trying to store in multiple vectors?

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C++ :: Looping Through A Vector Of Object Pointers

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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C++ :: OpenGL - Does Vertex Array Object Store Enabled Attributes

Jan 8, 2014

Does the VAO (glGenVertexArrays/glBindVertexArray/glDeleteVertexArrays) store the enabled/disabled state for the Vertex Attributes (glEnableVertexAttribArray/glDisableVertexAttribArray) or should I re-enable them every time?

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C++ :: Store Reference To Const Object In Class As A Member Variable?

May 27, 2014

i want to store reference to a const object in my class as a member variable, as follow:

I basically want a readonly reference to |Data| in Device object.

Code:

class Device {
Device(const QList<QSharedPointer<Data>> & dataList) : _listRef(dataList) {
} protected:
const QList<QSharedPointer<Data>> & _listRef;
}

This does not allow me to initialize _listRef as something like NULL when it is not applicable.Also, i must change all my constructors and its child class to include an initialization of _listRef!!

What is the alternative? Is pointer the nearest? which of the following should be used?

Code:
const QList<QSharedPointer<Data>> * _listRef;
or
const QList<QSharedPointer<Data>> *const _listRef;
or
const QSharedPointer<QList<QSharedPointer<Data>>> _listRef; ????

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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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C++ :: Store A Reference Variable As Member Variable Of Interface Object

May 1, 2013

I am having trouble compiling my interface. I am trying to store a reference variable as a member variable of the interface object. Compiler says that the variable has not be initiated correctly.

LCD inherits from VisualInterface which is expecting a DisplayDriver object to be passed in (DisplayDriver is another interface, but thats not important).

I pass the displayDriver object in when LCD is instantiated in maininterfaces.zip

I was pasing it before as a pointer but was told that this could cause me problems with memory leaks and a reference was better, but now I cant seem to get it to compile.

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C++ :: Scope Of References?

Apr 22, 2013

Did a little Googling on this but couldn't find anything definitive. Is it safe to do something like

Code:
void MyClass::myFunc(){
my_type_t &foo = some_obj->get_member_reference();
store_for_later(&foo);
}

Then at some pointer later in execution, another function uses the pointer passed to store_for_later.

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C++ :: Swap Between Two References?

May 28, 2013

I have the following code segment:

Code:

void Swap(Number& num1, Number& num2)
{
cout<<"Before swap:"<<num1<<" "<<num2<<endl;
Number& temp=num1;
num1=num2;
num2=temp;
cout<<"After swap:"<<num1<<" "<<num2<<endl;
}

[code]...

to which the output is:

Code:

Before swap:13 11

After swap:13 11

13 11 that seems confusing.

why doesn't Swap() swap the two Numbers?

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C# :: Programmatically Add Dll References?

Jan 11, 2014

I am trying to make a utility program for work that will update multiple projects with local dll references. Basically I work with two solutions (for talk sake solutIon1 and solutIon2). Generally solutIon1 will reference the dll's built In solutIon2 which reside on a server. However for debugging proposes I sometimes need to D/L the solutIon2 projects and build them local-ally, so that I can reference the solutIon2 dll's local-ally (this Is so that I can easily attach the dll and step Into the code). However this require changing the reference paths, so that I am pointing to the local-ally built dll's, which Is quite a laborious task.

So the question is how would I update references in solution1 from the program that I am making. I don't really know what to start reading about as I have never done anything like this before.

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C++ :: Vector Of Pairs Of References?

Jun 19, 2014

I am attempting to combine two vectors into a vector of pairs. I want to be able to alter the first and second of each pair and have those alterations reflected in the original vectors. I thought the following code might work but get compilation errors about a lack of viable overload for "=" for the line with the call to std::transform:

void f()
{
std::vector<int> a = {1,2,3,4,5};
std::vector<int> b = {6,7,8,9,0};

[Code].....

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C++ :: Declaring A Valarray Of References?

Sep 26, 2014

Is it permissible to declare, for example, `std::valarray<int&>`? If so, how do I initialize such if the `valarray` is a class member?

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C++ :: What Are Rvalue References And Temporary Objects

Dec 30, 2014

What rvalue references are? How are they useful? What are temporary objects?

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C++ :: Testing For References To Identical Objects

Jun 18, 2014

I am checking to see if two references are bound to the same object. My instincts tell Me, "Check their addresses. If they match, they are bound to the same." At the same time, I have not found anything in the C++ standard which would support this approach. Am I missing something? Is there wording which backs up My instincts? Is there a standard function to do this?

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C++ :: Parameter Pack Of Constant References

Aug 20, 2013

I have this basic prototype:

struct int_wrapper{int i;};
template <const int_wrapper&... IPack>
void display_all(const int_wrapper&, IPack...);

But when I try to compile it, the compiler says IPack is not a type on the last line. Are packs of references not allowed?

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C# :: Move Class To Its Own Project And Keep Its References?

Apr 3, 2014

I was wondering if there is way to convert a C# class to its own project and it automatically keeps its references.

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C++ :: Range-based Looping Over Container Of References?

Mar 6, 2015

Is it possible to create a class that stores (non-const) references to some objects and enables users direct access by using range-based for loops on them?

Code: class container {
public:
void add(int& value);
void remove(int& value);
...
};
int main()
{
container c;
for (auto& value:c) {
// `value' should be accessible as type `int&' instead of being a pointer, `std::reference_wrapper<int>' or something like that
}
}

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C++ :: Passing Variadic References To Template Function?

Dec 14, 2014

I'm having some problems in understanding how the code below works and why it produces the output it produces.. What I'd expect is that both functions, namely `add_1' and `add_2', would print the same output; but I've been proven wrong :/ So why does the second one get different memory addresses for the same variable?

Code should be self-explaining:

Code: template<typename... Types>
void add_1(Types&&... values)
{
// by the way: why do i have to use `const int' instead of `int'?
std::vector<std::reference_wrapper<const int>> vector{
std::forward<Types>(values)...};
std::cout << "add_1:" << std::endl;
for (const auto& value:vector) {
std::cout << &value.get() << std::endl;

[code].....

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C++ ::  2 Errors In Passing Values / References To Function

Jan 28, 2014

#include "stdafx.h"
#include <iostream>
#include <math.h>
#include <time.h>
#include<iomanip>
#include<array>
#include <algorithm>

using namespace std;
const int AS = 6;
void FillingRandomly(int (*)[AS]);
void printing(int (*)[AS]);

[Code] ....

Basically I have to create an array, fill it, and then print it on screen. The tricky thing is that need to use pointers to fill it and print and later on sort it. My problem is that with this code is that i get

Error2error C2109: subscript requires array or pointer typec:userspcdesktopusbanthonydocumentsvisual studio 2012projectsessaieessaieessaie.cpp55
and
5IntelliSense: expression must have pointer-to-object typec:UserspcDesktopUSBAnthonyDocumentsVisual Studio 2012ProjectsEssaieEssaieEssaie.cpp55

Whenever I try to run it.

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C++ :: RValue - References As Return Values Of Functions

Aug 13, 2014

I am trying to understand RValue-references as return values of functions. First let's consider a simple function, that transforms a string into upper case letters.

const std::string
toUpper(std::string orig) {
std::transform(orig.begin(), orig.end(), orig.begin(), ::toupper);
return orig;

[Code] .....

It compiles, but I get the output 0 . Here I am wondering why the code above does not move the substr correctly while the code below does (prints out 1):

const std::string&&
no_sense(std::string abc) {
abc = abc.substr(1, 1);
return std::move(abc);

[Code] .....

In both cases abc is a temporary object inside of the function and gets deleted after the function is left. But why does the second version work and the first one does not?

cat.substr(1, 1)

And as my last question. Why doesn't

return std::move(abc.substr(1, 1));

work?

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C++ :: Why Cannot Dynamic Memory Allocation Work With References

May 5, 2013

Why cant a dynamic memory allocation work with references? I was told that references work with const pointers deep down so shouldn't this be legal code?

int &&a=new int;

My compiler says that a entity of int* cannot be used to initialize a entity of int&&?

Does that mean that the compiler thinks of them as different types except deep down a reference is implemented with a pointer? Is this right?

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C# :: Cyclic References In A Database Access Layer

Jan 21, 2015

I'm looking to implement a Database Access Layer for the project I'm working on, it's a mature project and I'm trying to simplify the database access and as far as possible and remove the Database logic from the Business logic.

Bringing in an ORM solution isn't an option at the moment so I'm looking at bringing in DAO objects to break the coupling. The problem I can't get around in my head is how to avoid Cyclic references

We currently have 2 projects

BL contains types such as Customer, Component and Product which need saving to the Database, the Database project can't know about these items or it would create the cyclic dependency.

I tried adding Dao items to the DB project to mirror these items and to also mirror the DB structure but that requires that the BL project knows how to convert between it's own types and the DAO types which is something I'd like to avoid.

I also tried inserting a third intermediate project that would control the conversion and saving, I called it my DAL project and tried adding functions that would take the BL item and perform CRUD operations but again I ran into the cyclic dependency issue.

My ideal solution would be that the BL project would just have to call a function along the lines of "SaveCustomer(Customer inCustomer)" and not have to worry about doing any conversion.

Is there a project structure that would allow for this?

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Visual C++ :: No Circular References But Undeclared Identifier

Jun 11, 2014

Each of my header includes is protected by directives. I think I don't have to include Boolean in my work space because it is already included in the external dependencies section. and the Boolean.h is in the include path.

MachineShop, Boolean etc got undeclared identifier error

Tried to comment out the directives, to no avail.

Code:
#include <iostream>
#include <string.h>
#ifndef BOOLEAN_H_
# include "Boolean.h"
#endif
#ifndef PROCESS_H_
# include "Process.h"
#endif
#ifndef MACHINESHOP_H_

[Code] ....

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C++ :: Data Type Size - Performance With References

Aug 16, 2012

Here's what I'm trying to do : A simple readout that shows the input/feedback values for 10 different sensors (i.e. a motor, a thermocouple, light sensor, etc).

What I got so far:

The data is stored in 2 different arrays:

One array is a 2D string array that stores descriptions, and won't be changed:

Sensor ID, Sensor Type, Input Signal, Feedback Signal
["A"]["Motor"]["PWM Signal"]["RPM"]
["B"]["Thermocouple"]["N/A"]["TempC"]
etc

The second array is another 2D int array that stores all the data values:

Input Signal, Feedback Signal
[0][0] // for Sensor A, Input is 0 PWM, 0 RPM read from sensor
[0][25] // for Sensor B, Input is 0, 25C read from sensor
etc

My question: I'd like to re-write the code to incorporate the new things I learned in c++. Right now, the descriptions for all 10 sensors are in 1 array and the sensor values are in another array. If I use pointers to access the values, is there a performance difference between:

1. Keeping it as is, with 2 2d arrays
2. 1 big structure that has descriptions and sensor values for all 10 sensors (i.e. combining everything into 1)
3. 1 parent class, and 10 different objects for each sensor (i.e. splitting into 10)

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