C++ :: Lvalue Reference Bind To A Rvalue Object?

Sep 10, 2014

Trying to understand the lvalue and rvalue references, and come up with some strange codes, which compile and run, but is confusing to understand.

Define this class Thing:

class Thing {
public:
Thing(int k = 0): i(k) {};
~Thing() { std::cout << "destroying Thing (i=" << i << ")" << std::endl; }
int getValue() const { return i; };
Thing &getMe() { return *this; };
private:
int i;
};

and a non-member function:

Thing construct_Thing10() {
Thing t(10);
return t;
}

Then these two lines in main():

Thing &thg=construct_Thing10().getMe();
std::cout << "member=" << thg.getValue() << std::endl;

The output is:

destroying Thing (i=10)
member=10

My understanding is that the rhs of line 1 construct only a temporary object. getMe() then return the reference of this temp object and bind it to thg (as a lvalue reference). After line one, the temp object is really destroyed (hence the first output line). At this point thg is really binding to a destroyed, invalid object. But somehow the 2nd line still prints the correct value of 10 is because the memory storage is not yet corrupted (still holding the previous value). Is this correct?

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C# :: Constructor Object Reference Not To Set Instance Of Object

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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C Sharp :: Object Reference Not Set To Instance Of Object?

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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C# :: Object Reference Not Set To Instance Of Object?

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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C/C++ :: Get Reference To Text Object With The Name Of Object?

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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C++ ::  Reference To Dynamic Object

Jan 13, 2014

All entities need to be stored in the dynamic memory. I managed to force this by making the constructor private and by adding a static method which dynamically creates an object and returns a pointer. But it is most likely that the user will want to make them dynamically and we still have the following problem.

entity* player = entity::create();
(*player).setPosition(something);
(*player).act();
(*player).draw();

You get the point, having to dereference the pointer before each call becomes painful. So I thought about this... Instead of returning a pointer, I can return a reference. Then the code is much cleaner.

{
entity& test = entity::create();

// do stuff...
test.act();
// more stuff...

test.destroy(); // deletes the dynamic object
}

I put this code between brackets. That's because we must make sure the reference test doesn't exist after destroy is called, because destroy() makes it invalid. This is fully functional and won't cause any problem as long as the user doesn't forget to never call any method on a destroyed entity. But it's evil code. Would you risk it, or is there another way around?

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C++ :: Returning Object By Reference

Jan 25, 2014

When returning an object by reference, only the address of the returned-object is returned, and that way we spare pushing a large object into the stack, and also spare time of pushing and popping large object to/from stack.

But what happens when the object that receiving the returned-object, is not a reference, but a 'regular' object?

How is the content of the returned object copied into the receiving object?

See for example in main, wid vs rwid. (I know in the case the returned-object is just one variable, there's no need to return it by reference, but its for simplifying the code).

class Rectangle {
public:
Rectangle(int w=0, int h=0);

[Code].....

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C++ :: Reference Count Of Object?

Jun 24, 2014

I have a question regarding reference count of an object. How i'll be able to know that how many pointers are pointing to my object.....

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C/C++ :: Returning Reference To Object

Aug 1, 2014

I have this method that takes a pointer to a class object and right now when printing it, it's returning the location in memory 0x100300000. I've tried tweaking the function in a few different ways but I cant get it to return the object instead of the location.

Here's the vector that addSale accesses and the deceleration of the addSale ethod in the employee class.

class Employee{
protected:
....
public:

[Code]....

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C++ :: Pass Class Object By Reference

Jun 25, 2013

I am having trouble working with third party dll's, libs and header files. I am trying to call a function.here is the function that is suppose to be called.

bool COAuthSDK::GetRequestToken(CClientDetails &objClientDetails)

it has this info of what it needs :

Name IN/OUT Description
m_environment IN Optional. Possible values are SANDBOX (default) and LIVE.
m_strConsumerKey IN OAuth consumer key provided by E*TRADE
m_strConsumerSecret IN OAuth consumer secret provided by E*TRADE
m_strToken OUT Returned by the function if successful
m_strTokenSecret OUT Returned by the function if successful
m_strCallback IN Optional; default value is "oob"

here is the COAuthSDK header

#ifndef _OAUTHSDK_H_INCLUDED_
#define _OAUTHSDK_H_INCLUDED_
#include "ETCOMMONCommonDefs.h"
#include "ETCOMMONOAuthHelper.h"
using namespace std;

[code].....

when I try to build the function it says that its in the dll's so I know I have to call it.here is the link to the build site if needed URL....

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C++ :: Pass Class Object By Reference?

Mar 17, 2014

I'm trying to pass a class object by reference.

total = mathfunction(i);
}
double mathfunction(retirement& j)
{
double R = 0.00, m = 0.00, r = 0.00, t = 0.00, totaled = 0.00,
numerator = 0.00, denom = 0.00, temp = 0.00;

[Code]....

I only tried to pass by reference because I figured passing by value would be a larger pain in the neck.

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C/C++ :: Passing A Stream Object By Reference?

May 5, 2014

I need to create a function in my program to open an input file and another function to open an output file and I need to use the files in other functions so Im trying to pass the stream object by reference but then i need a condition that tells the compiler not to reopen the file because then it will delete everything and make me input the file names again. Heres the two functions.

void InputFileOpen(ifstream &inFile) {
string file_name;
if(!inFile.is_open()){
cout<< "Enter the input file name: ";
cin>> file_name;
inFile.open(file_name, ios::in);

[code]....

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C Sharp :: Making A Reference To Object

Mar 19, 2014

In a project I'm building I have 4 datagrids which I'm using and where I'm updating information manually, so not from a database or a list.

Now to make it a bit easier I would like to use one generic sort of variable to prevent having to write the same code 4 times.

So if I have 4 datagridviews DataGrid1 through DataGrid4 I would like to be able to assign one of those Datagridview to a general object that has all of the properties and methods in it.

I was thinking of using something like this:

object DataGrid = DataGrid1  
DataGrid.Rows.Add("INFO");  

But that doesn't work.

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C++ :: Error Passing Object Reference

Nov 23, 2013

Code:

#include <Data.h>
int main(int arg_count, char** argv) {
if(arg_count!=3){
cerr<<"Files misisng
";
exit(1);

[code]...

This actually should work, because it is passing address of polymorphisms object.I have tried changing prototype of test in Data.h, but failed.passing object address/pointers in C++.

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C# :: Rain Application - Object Reference Not Set To Instance Of Obj

Mar 2, 2014

I'm trying to make a "Rain" application, by drawing some lines on the form, and then they must fall. So here is my start code:

public partial class Form1 : Form {
public Form1() {
InitializeComponent();
}
Random r = new Random();
Graphics paper;
Line line;

[Code] ....

So when I start debugging I get the "Object reference not set to an instance of an object." error. If I remove the comments lines at "timer1_Tick" this error doesn't appear of course. What can I do to escape from this because it follows me everywhere I go />. I tried to make with arrays, but same problem.

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C++ :: Unable To Pass Reference Of Object Ifstream To Constructor

Jan 30, 2013

I'm trying to pass an reference of the object ifstream to my constructor as such:

// myClass.cpp
int main(){
ifstream file;
myClass classobj = myClass(file);}

I am defining the constructor as follows, in myClass.cpp:

myClass::myClass(ifstream &file){
// do stuff
}

I get the error of "No overloaded function of myClass::myClass matches the specified type."

Also, when I build the program, it tells me "syntax error: identifier 'ifstream'"

Also, I made sure I included this:
#include <iostream>
#include <fstream>
#include <sstream>

What am I doing wrong? How can I pass an ifstream reference to my constructor?

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C++ :: How To Create A Function That Takes A File Object As A Reference Parameter

Feb 21, 2013

I have a school project in which need to create a function that takes a File Object as a Reference Parameter. Supposedly, it should allow me to read the first piece of data from others separated by a space from a file. The later be able to continue reading from the next piece of data.

I know how to set things up to read from the data file, such as using

Code:

#include <iostream> , and

Code:

ifstream inputFileName;
inputFile.open ("nameOfFile");

I also understand how to pass a variable by reference to a function. But I simply cannot put the two items together!

I tried using

Code:

void getFileInput (ifstream &); //parameter
getFileInput ("nameOfFile") // call
void getFileInput (ifstream &dataFileName)

In the function I used

Code:

ifstream inputFile;
inputFile.open (dataFileName);

I'm just not getting an understanding of this concept!

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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++ :: Non-static Member Reference Must Be Made Relative To A Specific Object

Mar 4, 2012

Code:
class A
{
std::map<std::string, Unit*> aMap;
class B

[Code] .....

This code snippet results in "A non-static member reference must be made relative to a specific object". When I make callA() static, this error goes away, but there is problem with aMap.

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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++ :: 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# :: How To Bind In RadioButton From List

Jul 4, 2014

I want to ask a question about radiobutton binding in wpf . Im am listing one radiobutton but i wanted to list all elements.

My QuestionType class. Select radiobuttonid and buttonname from excel table. And add to list.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

[Code].....

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C# :: Bind XML Response To Grid View

Nov 11, 2014

I have been trying to bind an xml response from a web service to a gridview but to no success. bellow is my code

soapInvoker.setMethod("GetAgentProducts");
XDocument AgentproductsRequest = SoapMethods.GetAgentProducts(pin);
XDocument AgentproductsResponse = soapInvoker.CallSoapServiceInternal(AgentproductsRequest);
XDocument xmlDoc = new XDocument(AgentproductsResponse);
var vrresult = from a in xmlDoc.Descendants("product")

[Code] ....

And I always get an error that is not explained dont know whether is coz i bootstrapped my master page or what but all errors caught where there are it shows this Runtime Error

Description: An exception occurred while processing your request. Additionally, another exception occurred while executing the custom error page for the first exception. The request has been terminated.

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C Sharp :: How To Bind DropDown List

Feb 16, 2013

<asp:TemplateField HeaderText="Group_Id"> 
<ItemTemplate> <asp:Label ID="G1" runat="server" Text='<%# Eval("Group_Id") %>'></asp:Label> 
</ItemTemplate> <EditItemTemplate> <asp:TextBox ID="G2" runat="server" Text='<%# Eval("Group_Id") 

[Code] ....

on running i find this error

Compiler Error Message: CS1061: 'ASP.webform12_aspx' does not contain a definition for 'Group_Item_Name_SelectedIndexChanged' and no extension method 'Group_Item_Name_SelectedIndexChanged' accepting a first argument of type 'ASP.webform12_aspx' could be found (are you missing a using directive or an assembly reference?)

Source Error:

Line 143: </EditItemTemplate>
Line 144: <FooterTemplate>
Line 145: DropDownList ID="G3" runat="server" AutoPostBack="True"
Line 146: onSelectedIndexChanged=" Group_Item_Name_SelectedIndexChanged" Width="133px">
Line 147:</asp:DropDownList>

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C/C++ :: Lvalue Required For Function Main

Sep 5, 2014

I actually am wanting to practice on a 2 dimension char array. so, I am using the below program and getting the error - Lvalue Required For Function Main

#include <stdio.h>
#include <conio.h>
#include <string.h>
char varStringArray[1][5];
int main(void) {
clrscr();
varStringArray[0] = 'a';
printf("%c", varStringArray[0]);
return 0;
}

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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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