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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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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Sep 6, 2013
Example code:
Code:
#include <iostream>
#include <vector>
using namespace std;
class A{
[Code]....
I read somewhere, that we can imagine the reference as a pointer to the vector. So, my question is:
Let's assume that instance of class A, named a, was created with new. We call a.getV() to foo and then we call the destructor of a. foo is safe? Is the copy constructor of std::vector called?
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Feb 15, 2015
#include<iostream>
using namespace std;
int &fun() {
int x = 10;
return x;
}
int main() {
fun() = 30;
cout << fun();
return 0;
}
The code outputs 10.
Shouldn't it show an error because x is created locally on stack and gets destroyed on function return?
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Dec 17, 2013
Write your question here.
#include<iostream>
using namespace std;
void getInput(int& numOfDays, double& itemPrice);
[Code].....
So this program is supposed to calculate the price of an item, and return it back as the variable total of type int. but for some reason it gives me a weird output on total. And am i using call by reference correct?
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May 14, 2012
struct emp {
char name[20];
int age;
float sal;
}e1 = {"hello", 24, 2345.67}, e2 = {"hi", 34, 45678.89};
[Code] ....
Query: I am unable to get emp &fun() and fun() = e2...
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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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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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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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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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Nov 24, 2013
Code:
class Main{
class B b_obj;
C c_obj=b_obj.test("some",89); // I cannot get this done.!
}
Below are .h files:
class B{
public:
C* test(const char *, int); /// this doesn't work
constructor
//member variables
[Code] ....
However, map<string, vector<bol>> test(const char *, int); works.I know second thing will work, but how to take reference of class object?
I have include .h file in main, B and C, wherever it is required.
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Oct 30, 2014
while(!secList.empty()){
Security se = Security();
se = secList.extract(); // CRASH
cout << "Security info: " << se.security << endl;
cout << "Transaction List: " << endl;
while(!se.tranList.empty()){
Transaction tr = Transaction();
[code]....
my program crash when it try to assign the return value of the function to the local value. extract function does return correct value, but it just crash when done executing.
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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