C++ :: How To Design A Smart Pointer Class
Nov 11, 2014
smart pointer class is the one that take in charge of release allocated resource when itself destroyed.
recently,i want design a smart pointer class, it take in charge of release resource allocated by new or new[].
my problem how to design destructor, you should determine the pointer ptr is pointer an array or a single object.
the structure of this smart point class may be:
template<class T>;
class smart_pointer{
public:
smart_pointer(T* p):ptr(p){};
~smart_pointer(){
[Code] ......
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Jul 30, 2014
I just want to know if there is any real difference between the two below, if yes, when would i use one over the other? I would thought the "&" is pointless in below function, as far as the data is concerned.., the only things is with "&", if the pointer address value is changed in Test function, it will affect the caller's copy of data. Both function should behave the same if data is changed.
Code:
Between
void Test(QSharedPointer<Data> data)
{
}
and
void Test(QSharedPointer<Data> & data)
{
}
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Oct 8, 2014
Here is my code,
Code:
class A {
public:
void display() {
cout<<"A"<<endl;
[Code] .....
The compiler error is "error C2039: 'display' : is not a member of 'SP<T>'". What am I missing here?
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Jan 24, 2014
Writing a smart array class for my C++ class. I'm running into a problem where the constructor apparently throws the wrong exception. Compiled on G++ with C++11 extensions enabled.
Code:
// headers
#include <iostream>
#include <utility>
#include <cctype>
// stuff we need from namespace std
using std::cout;
using std::cin;
[Code] .....
When I try to check the error-handling code, when I enter a size less then two, Array's ctor throws InvalidSize, and gets caught, all good. But when I enter a letter, the ctor also seems to throw InvalidSize!
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Jun 8, 2014
I want to write a command line parsing library that is very flexible in terms of parsing style but I'm not able to design a mechanism that satisfies this requirements.
Generally i want to have a class that contains all the necessary information about how the command line has to be parsed.
Code:
// draft
class style {
public:
enum class type { // the basic style type
[Code] ....
Need completing the draft shown above, because for every basic style type there is an own set of extensions that applies only to this one specific style type.
Code:
// how a style object should be created
style parsing_style(style::type::posix, style::extension::gnu|style::extension::subcommand);
How to design the class. (using c++11 features like std::enable_if is fine)
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Apr 24, 2013
The program is supposed to design a class that can be used that can represent a parabola.
Code:
#include <iostream>
#include <iomanip>
#include <cmath>
#include <fstream>
#include <cstdlib>
#include <cstring>
using namespace std;
class Parabola {
public:
Parabola( double, double, double );
[Code] .....
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Aug 7, 2014
I have a Class called 'DataManager' which contains a list of my 'DataItem' objects (this are created by an XML file).
I have also created some custom controls which, among other things, has a property to link it to a "DataItem" object.
My question is, is it possible to create an instance of my DataManager class at design time (which runs all the code as it would at run time to create all the DataItems from the XML)?
I want to do this so that I can update my DataItem property in my custom controls to use a UITypeEditor which then allows me to link to a DataItem at design time.
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Oct 17, 2013
In the following code example of the State Design Pattern, in the main code at the bottom it defines an instance of class Machine, and then calls Machine::off;. Why doesn't it instead call fsm.off;?
Machine fsm;
Machine::off;
Then I tried imitating that by adding a class Abba, and then doing:
Abba a;
Abba::DoStuff();
but that didn't work. Why?
Full code example:
// StatePattern.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <iostream>
using namespace std;
class Machine {
class State *current;
[Code] ....
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Jul 8, 2013
Assignment: Design a class to store measurements. The class should have two data items, feet and inches, both integers. The class must make sure that the number of inches never gets below zero or above 11. If inches is outside that range, adjust feet accordingly. (Yes this means feet might be a negative number.)
Create a default constructor and one which receives one integer, a number of inches.
Overload the following operators: addition, subtraction, equality, inequality, incrementation (both pre and post) (should add one to inches), and output (in the form of: F’I”)
Code:
#include <iostream>
using namespace std;
class measurements {
private:
int inches;
double feet;
[Code] ....
I am getting a LNK2019 error and an LNK1120 errors:
Error 1 error LNK2019: unresolved external symbol _main referenced in function ___tmainCRTStartup
Error 2 error LNK1120: 1 unresolved externals
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Jan 31, 2013
I need to create a GlobalConfig class. But I want to derive from it in another class.
Here's an example:
public class BaseConfig {
public string GlobalPath {get; set;}
}
public class ConfigA : BaseConfig {
public string pathA {get; set;}
}
public class ConfigB : ConfigA {
public string pathB {get; set;}
}
The idea behind is that I don't want to write the code multiple times and what's more important in class ConfigA I want to set GlobalPath and have access to it in ConfigB.
In other word I want class ConfigB to have a property GlobalPath which was set in class ConfigA.
To clarify I want to have only one object of Config in memory.
When I set BaseConf.GlobalPath to 'A', I want to access it from ConfigB.GlobalPath and also get 'A'.
I always design GlobalConfig as a static class, but static classes can't be inherited. So I tried to implement Singleton Pattern, but ConfigA can't find constructor of class BaseConfig because it's private.
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Dec 2, 2013
I have been thinking about this all day and I am yet to come up with a good solution. So, I need to design an image class which should work with various data types (int, float, double etc.) and can also be multidimensional (2, 3, 4, 5). So, what I did was generate a template image class as follows:
Code:
template<typename T, int dimensions=3>
class Image {
private:
T * data;
};
Anyway, now I have various image formats that I want to support, so the easy thing to do is create a Factory sort of object which will call eventually generate the correct image.
So I want to create various image classes called ImageType1, ImageType2 etc. which will take the input image and generate the correct Image object. However, I do not want these objects to be templated because they need to be passed from functions and be used in a generic way.
So, at run time I will need to be able to do this…
Code:
class ImageType {
public:
ImageType() {
PolymorphicImage * image = new Image<float, 3>();
}
private:
PolymorphicImage * image;
};
So, I want my ImageType classes to contain the Image object and be able to generate it with the right template arguments at run time. Is there any way to do this without having multiple specialised definitions for ImageType?
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Feb 6, 2015
I create an instance of a base class (not derived class) and assign it to base class pointer. Then, I convert it to a pointer to a derived class and call methods on it.
why does it work, if there is a virtual table?
when will it fail?
// TestCastWin.cpp : Defines the entry point for the console application.//
#include "stdafx.h"
#include <iostream>
class B
{
public:
B(double x, double y) : x_(x), y_(y) {}
double x() const { return x_; }
[Code] ....
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Nov 29, 2014
Design, implement, and test a class that represents an amount of time in minutes and seconds. The class should provide a constructor that sets the time to a specified number of minutes and seconds. The default constructor should create an object for a time of zero minutes and zero seconds. The class should provide observers that return the minutes and the seconds separately, and an observer that returns the total time in seconds (minutes x 60 + seconds). Boolean comparison observers should be provided that test whether two times are equal, one time is greater than the other, or one time is less than the other. (You may use RelationType and function ComparedTo if you choose). A function should be provided that adds one time to another, and another function that subtracts one time from another. The class should not allow negative times (subtraction of more time than is currently stored should result in a time of 0:00). This class should be immutable.
this is one of my main errors: Error1error C2653: 'Time' : is not a class or namespace namec:userskdesktop
oane statecisp 1610visual studioschapter 12 assignmentchapter 12 assignmentchapter 12 assignment.cpp131Chapter 12 Assignment
//The implementation file ImplFileTimeClassAsgnt.cpp:
#include "Time.h"
#include <iostream>
using namespace std;
Time::Time() {
mins = 0;
secs = 0;
[Code] ....
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Sep 9, 2013
I am struggling with how to efficiently design my class objects to support the outlining of a collection of items. The collection would be sorted but would also have the ability to indent and outdent individual items representing a Parent and Child relationship (see attached).
An item could indent up to 5 levels deep. A summary level would be considered a Parent while items below the summary level would be consider as children.
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Aug 19, 2014
I am attempting to implement function pointers and I am having a bit of a problem.
See the code example below; what I want to be able to do is call a function pointer from another pointer.
I'll admit that I may not be explaining this 100% correct but I am trying to implement the code inside the main function below.
class MainObject;
class SecondaryObject;
class SecondaryObject {
public:
[Code]....
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Mar 21, 2015
In this book, item 3 is about never treat arrays polymorphically. In the latter part of this item, the author talks about the result of deleting an array of derived class objects through a base class pointer is undefined. What does it mean? I have an example here,
Code:
class B
{
public:
B():_y(1){}
virtual ~B() {
cout<<"~B()"<<endl;
[Code] ....
This sample code does exactly what I want. So does the author mean the way I did is undefined?
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Aug 21, 2014
I am new to smart pointers and have a question.If you push a smart pointer onto a vector and then some where later pop it back off it will delete the memory right?
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Aug 3, 2014
I'm writing quite a large program that needs to work with very large arrays (up to 100 million integers). It is necessary that i can access every point of the array directly (without running through the array) and that I use as little memory as possible. I first wrote the program with pointers that point to allocated heap memory. It works fine but now I wanted to use smart pointers instead (so I'm sure to have no memory leaks). Here's a simple visualization of my problem:
#include <iostream>
#include <memory>
using namespace std;
unique_ptr<int[]> upArray;
int main() {
int nArrayLength = 10;
[Code] ....
There are 2 things that do not work how I would like the to:
1. It wants me to assign the heap memory in one step: unique_ptr<int[]> upArray(new int[nArrayLength]); But I'd like to have the unique_ptr in my Class_Declaration before I know the array length and allocate the memory later.
2. *(upArray + i) = i;
cout << *(upArray + i);
Those lines don't work! How else can I do it.
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Nov 29, 2013
My program is a basic MFC AppWizard (exe) created project in VC++ 6. In MainFrm.cpp, I am trying to access some user defined CMyView member functions. However when I try to do the standard procedure to get the CMyView pointer in MainFrm.cpp, I get the " ... 'CMyView' : undeclared identifier" error. To resolve this, I add " #include myView.h " at the top of MainFrm.h which then produces the following errors:
Code:
myview.h(21) : error C2143: syntax error : missing ';' before '*'
myview.h(21) : error C2501: 'CMyDoc' : missing storage-class or type specifiers
myview.h(21) : error C2501: 'GetDocument' : missing storage-class or type specifiers
What do these errors mean? Is there a simple way to access CMyView member functions from CMainFrame?
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May 19, 2013
When i try to compile this code it gives me a error during run-time saying "*program name* has stopped working"
Code:
#include <iostream>
#include <memory>
using std::cout;
using std::endl;
using std::unique_ptr;
[Code] .....
Why is this happening? Also why do you need the asterisk on smart pointers to assign them a value? Is it just because, or is there a reason.
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Jun 28, 2012
I'm trying to implement a class hierarchy and a wrapper class with a pointer to the base class. The base class has operator< overloaded and the implementation makes use of virtual functions as some of the logic for sorting is in the derived classes. Unfortunately, when trying to use the base class operator< from the wrapper, I get a "pure virtual method called".
Below code is meant to illustrate my problem. Unfortunately it crashes on me (upon destruction of vec) and I cannot quite see, why. So two questions:
1. spot the error I made in the code below (having lived in Java-land for the last 5 years, I'm sure I just did some stupid error)?
2. How can I implement Wrapper::operator< to use Base::operator<? I know I could write a function and pass it to sort but I'm interessted if there is a way to actually use Base::operator<.
Code:
#include <vector>
#include <algorithm>
#include <cmath>
[Code].....
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Oct 3, 2012
I have encountered a problem I can't see to solve. I want to access a function and can't seem to find the right combination to get me there. Here is what I am looking at:
CFoo1::CFoo2::GetStrDataC(int nRow) const
How do I call the GetStrDataC function from another class?
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Mar 14, 2012
Suppose I'm writing a program designed to simulate a large company. I'm interested in tracking each company employee by the location where they work. This company has perhaps a thousand different locations:
class Employee {
public:
AccessorFunction1(); // does something
AccessorFunction2(); // does something different
AccessorFunction3(); // does something completely different
protected:
// Some data
[code]....
Once employees are created and pointers to them are saved in the proper Location vector, I write an accessor function, OrganizeLocation(), designed to do a number of operations on a given vector. The problem is, I have maybe a thousand vectors. How do I call this function and specify which vector I want?
Currently, I'm using this clunky solution:
void Company::OrganizeLocation(int a){
switch(a) {
case 1: {
for(unsigned int i=0; i<LocationA.size(); i++) {
LocationA[i]->AccessorFunction1();
LocationA[i]->AccessorFunction2();
LocationA[i]->AccessorFunction3();
[code]....
The key point here is that whichever vector I choose to operate upon, I'll do the exact same procedure every time. I hate this solution because it results in very long and repetitive code not to mention its very error-prone when you re-editing all those "LocationA 's into "LocationB/C/D/etc."
void Company::OrganizeLocation( string $WhichOne$ ){
for(unsigned int i=0; i<LocationA.size(); i++) {
Location$WhichOne$[i]->AccessorFunction1();
Location$WhichOne$[i]->AccessorFunction2();
Location$WhichOne$[i]->AccessorFunction3();
}
Or, if it can't be done in C++, is there a better design approach? Ultimately I need the Company object to hold multiple vectors but use one compact accessor function to perform operations on just one of them.
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Feb 20, 2014
I am trying to use smart pointers to sort and re-link potentially large data elements. I have defined a class in my code for smart pointers, as listed below:
template <typename T>
class sptr {
public:
sptr(T *_ptr=NULL) { ptr = _ptr; }
[Code] ....
The object I'm trying to sort is a singly-linked list containing class objects with personal records (i.e., names, phone numbers, etc.). The singly-linked list class has an iterator class within it, as listed below.
template <class T>
class slist {
private:
struct node {
node() { data=T(); next=NULL; }
[Code] .....
The following is my function within my list class for "sorting" using the smart pointers.
template <typename T>
void slist<T>::sort(){
vector< sptr<node> > Ap(N); // set up smart point array for list
//slist<T>::iterator iter = begin();
node *ptrtemp = head->next;
[Code] .....
I must have a bad smart pointer assignment somewhere because this code compiles, but when I run it, std::bad_alloc happens along with a core dump. Where am I leaking memory?
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Aug 2, 2013
I'm currently reading the C++ Guide for Dummies
Anyway right now I'm working with pointers and classes, and when I create a new pointer for my class it looks like this...
Pen *Pointerpen = new Pen;
But in the book they threw in this...
Pen *Pointerpen = new Pen();
Can you actually designate memory space for a function? Or was this a typo on their part? It's never come up before and they didn't explain it.
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May 18, 2013
A pointer to base class, if assigned to a derived class, only points to the base part right? So you can only use the base part of the derived class with that pointer and no methods from the derived class?
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