C++ :: Using Typedefs To Abstract Multiple Implementations
Jan 12, 2014
I am writing a program that aims to be cross-platform, so it supports multiple low-level implementations for certain operations. My initial approach is to write an abstract class to use as an interface, and inherit from that when writing specific implementations.
However, I realized that the specific implementation that I will be using is known at compile-time, and I to not need any polymorphic behaviour. I realized that I could just write this:
Code:
class Impl1 {};
#ifdef USING_IMPL1
typedef Impl1 Interf;
#endif
Clients would then go on using the Interf type, regardless of the underlying implementation. The only drawback that I can see is that my Implementation classes are not forced to conform to an interface, but the compiler will tell me anyway if I try to use, in my client code, a method that is not defined.
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Jun 13, 2014
I'm using some rather large external libraries, and I want to load them in my .cpp file only. so, my header looks like this:
namespace {
// hidden declarations
namespace geometry {
class Point;
class Polygon;
class Box;
//etc
}
}
In the declaration of the main class in that header, I merely use these as pointers or references. The .cpp file looks as follows:
// Boost
#include <boost/geometry/geometry.hpp>
#include <boost/geometry/geometries/polygon.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/multi/geometries/multi_polygon.hpp>
[Code] .....
This doesn't work however:
error C2371: '`anonymous-namespace'::geometry::Point' : redefinition; different basic types
1> e:..........NavigationMesh.h(10) : see declaration of '`anonymous-namespace'::geometry::Point'
What can I do to forward declare external classes like this?
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Jul 7, 2014
I recently noticed that I don't need to include the required header files inside header files that I have written myself. As as example, GLuint is defined using typedef unsigned int GLuint; inside glew.h. If I create a sample.hpp header file and mention GLuint without including glew.h, the compiler automatically works out that there is a typedef in glew.h. However, if I mention GLuint in a source file the compiler starts to complain. I have seen this happen in VS 2010 and 2013.
Edit: I should have mentioned that I am not including any other header files so I'm not indirectly including glew.h
In case you need to look at the code:
#ifndef CP_SHADER_LOADER_H
#define CP_SHADER_LOADER_H
namespace cp {
[Code].....
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Mar 5, 2014
If I seed with the same seed I want the same sequence of numbers no matter if I use GCC, Clang, VC++ or Windows, Linux, Mac. I think this is guaranteed by the standard engines in <random>.
I also want to be able to save the state of engines and restore them in a program compiled with a different compiler. I have been under the impression that the stream operators for the standard engines did not guarantee this kind of compatibility across implementations but after looking a bit closer I think it should work, assuming obvious stuff like CHAR_BIT == 8 and that the same character set is used.
When it comes to distributions like std::uniform_int_distribution and std::geometric_distribution I don't think I can rely on a consistent behavior. It looks like the standard only say what probability density function they should have. It doesn't explain how exactly the output should be calculated from the number that the engine produce. For this reason I don't think I can use any of the distributions in the standard library if I want a consistent sequence of numbers everywhere.
So am I correct that I can safely use the standard engines as long as I don't use the distributions? Or do I have to use a library with a fixed implementation to guarantee this to work consistently across compiler implementations?
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Oct 16, 2013
I am currently working on data abstraction. I was able to write a class (a simple clock, see Malik's C++ book, Chapter 12 for reference). As you can imagine, I am quite new to programming and C++.
Well, now I created a header file clock.h that includes the class definition and function prototypes as well as a implementation.cpp file with the implementation details of the class.
I managed to include all this in my program.cpp and compile it (using dev c++). Everything works exactly as I want it to.
So now my question is, how can I create ... I am not sure how it is called ... a header, but without revealing to the user how the functions are implemented. Basically the user should get a file (the object code of the header + implementation.cpp?) and simply #include it into his own program.
So instead of giving the original header + implementation.cpp to the user I want to hide how my class does its stuff and instead just provide some file that can be included and then used in a program (I will write a documentation how to use the class).
I am not sure how all this is called, I am sure there is some name for it...
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Feb 11, 2013
i need a function that will work for both dynamic and static implementations of a function to get the transverse of a matrix. so far, i have this
Code:
matrix transpose(matrix m)
{
int row, col;
row = m.com_dim;
col= m.row_dim;
}
[code]....
this works well with my static implementation, but when i try it in dynamic it gives me errors. the function has to be the same for both dynamic and static implementation
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Dec 28, 2012
two more questions
Code:
#ifndef PERFECTSIM_PARSER
#define PERFECTSIM_PARSER
#include <string>
#include <d3dx9.h>
#include <sstream>
#include <iostream>
#include "tinyxml inyxml.h"
using namespace std;
template<class T>
class GetValue {
protected:
virtual T get(TiXmlNode* pParent);
[code].....
1) Can't instantiate abstract class of GetVector3.
2) Don't you think the coding is very redundant ?
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May 13, 2014
I need to create a vector of pointers and hold the book objects in it. then i have a virtual function in my books which is a pure virtual in LibraryItems. When i try to add the books object in my code, i understand that since the scope runs out there is no object that is added. so when i run print it gives me an error.
#include<iostream>
#include "books.h"
#include "library.h"
#include <vector>
using namespace std;
int main(int argc, char * argv[]) {
vector<LibraryItems* >libraryInfo;
[Code] .....
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Feb 17, 2013
I have this header file called Shape.h containing these function declarations. and a Shape.cpp which contains the body of the function. I am not showing it since it is not needed.
//This is from Shapes.h header file
#ifndef SHAPES_H
#define SHAPES_H
#include <iostream>
[Code]....
I have this unfinished Main.cpp because the third line "JuanSanchez::Circle *pCar = new Circle; " is giving me a compiler error "error C2061: syntax error : identifier 'Circle' "
#include "Shapes.h"
int main()
{
const int arrayIndex = 4;
JuanSanchez::Shape *myShape[arrayIndex];
JuanSanchez::Circle *pCar = new Circle;
}
What Could be causing this error?
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Nov 11, 2014
I have the following code:
class Element {
public:
..
virtual unsigned NumberOfNodes() = 0;
[Code] ....
Is it possible to implement this better? All the element stuff can be static, but this is not possible with the abstract class. I want to have Mesh independent of a specific element. With the code above, if I have multiple meshes I have one instance of an element, e.g., Triangle for each mesh. Although they are all exactly the same.
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Oct 13, 2013
I am working on a project that requires me to create objects from a abstract class that has 2 child classes (that need to be derived). Any examples on how to do this? I looked online and the examples were pretty vague. the main error that I am getting is when I make a temp object with & in front of it (such as Employee &genericEmp) it throws a must be initialized error.
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Oct 3, 2014
I want to create an abstract base class having a member function that can accept a templatized structure as its parameter, something that according to C++'s rules can't be done for a good reason.
That good reason it is because an abstract base class is intended to provide interface rules to the classes that will derive from it and should not deal with data.
But how would you go about doing something like the following which is probably a reasonable design decision?
template<typename T>
class Matrix { /* ... */ };
class iFile {
public:
virtual ~iFile() {} = 0;
virtual void Process(const Matrix<T>&) = 0;
[Code] .....
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Feb 14, 2013
I am making a snake game just to give some context.
//LevelObject.hpp
class LevelObject {
public:
virtual void Update() = 0;
virtual void Draw(Canvas& canvas) = 0;
protected:
Vector3 location_;
[Code] ....
The problem I have is with the Size constructor and the abstract class LevelObject which size is a member of.
The compiler error I get is:
C:Program Files (x86)ProgrammingProjectsUniversityprg_interactivesnakey_takeysrc..inc..incPlayer.hpp|17|warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 [enabled by default]|
C:Program Files (x86)ProgrammingProjectsUniversityprg_interactivesnakey_takeysrc..inc..inc..incPlayer.hpp|17|warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 [enabled by default]|
[Code] .....
However I do invoke the copy constructor when I pass a variable of type size to the constructor in this line:
size_ = Size(s);
But the problem is that its complaining that the abstract class LevelObject doesn't invoke the constructor, which it shouldn't.
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Mar 5, 2015
.Theoretically speaking, we cannot create object of abstract class and even return an instance of it. But according to msdn documentation, WebRequest request = WebRequest.Create("Uri here");. In other word, with this statement, the create method return an instance of the WebRequest class, which is the abstract class.
As far as abstract class is concerned, there is no way for us to return an instance of the derived class within the abstract class or superclass, within the method of abstract class in particular. Since the abstract class knows nothing about the derived class. Unless the method is implemented within the derived class. Here is the statement HttpWebRequest request = (HttpWebRequest) WebRequest.Create("Uri here");
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Jun 22, 2012
I have an abstract class called Mbase and from it derived two classes: Sparse and Dense. Now I have an array in which its elements can be either Sparse or Dense. So, I delcared the array to have pointers to Mbase class. For example:
PHP Code:
Mbase** A;
Sparse* A1 = new Sparse;
Dense* A2 = new Dense;
A[1] = dynamic_cast<Mbase*>(A1);
A[2] = dynamic_cast<Mbase*>(A2);
Now, I have operator + defined in Sparse and Dense. but when I do
PHP Code:
A[1]+A[2]
I get that operator + is not defined for Mbase class. So, I tried to define it in the Mbase class
PHP Code:
class Mbase{
public:
void put()=0;
double get()=0;
Mbase operator +(Mbase A);
}
However, the last code does not compile complaining that it cannot declare a class of type abstract in Mbase operator +(Mbase A). I think this is because I am returning Mbase instance.
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Feb 28, 2013
coming from Java, my experience with the Classes in C++ is quite limited.
Thats why I am having trouble converting the following (simple!) Java-Program.
Most examples with linked lists I found on the web describe how to implement the LinkedList class itself. But my problem is different: I want to use such a Class (I have a LinkedList class available on my system which is presumably OK).
Code: package main;
import java.util.ArrayList;
public class Main {
public static void main(String[] args) {
BoxList<String> sl = new BoxList<String>(
new ArrayList<ABox<String>>());
sl.getList().add(
new BoxPair2<String>(new BoxPair2<String>(
[code].....
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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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Jan 26, 2013
when I should use pure virtual functions.On the one hand, "TOY" for example should be an abstract class since theres no such thing as "TOY" , there are "toy cars", "toy fighters" etc , but on the other hand I need to force it somehow to be abstract since theres no really a function that any toy should have and implement on his own way (except PRINT maybe).
when I should REALLY use pure virtual functions? And if I want to avoid people from creating TOY objects (for example), the only way is PURE virtual functions. right?
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May 6, 2014
The code below runs correctly (feel free to compile and run it yourself to see what it does). But when I turn Object abstract by uncommenting the line
virtual void foo() = 0;
It obviously won't compile. I want to use a copy constructor rather than restoring one data member at a time because I'm assuming that Object will have many, many data members (and also want to avoid extra responsibility when new data members are added to Object). Of course, using a pointer to Object in Memento will defeat the purpose of taking a snapshot.
#include <iostream>
#include <string>
#include <sstream>
#include <vector>
const std::string NAME = "Object";
[Code] .....
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Jul 27, 2012
As i have one Abstract base class say MyBase.
It have parameterized constructor with string value it have abstract method call.And I also have One child class say MyChild.
It does not have any constructor only one have public method and i want to call that parameterized constructor of base class onto child class.
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Oct 2, 2013
Imagine if there is an abstract class with a method (say output or print) which would be inherited by a few other classes. Later objects are created using the inherited classes, and the user wishes to call the above method twice, for eg (i) output/print to screen and (ii) output/print to a file. What is the best way to achieve that.
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Feb 27, 2014
I'm trying to implement a decision tree that gets doubles as input (in this sample code just random numbers) and returns a boolean value. At the nodes, I'd like to use various operators that can have different input and return types. I've implemented an abstract base class for the nodes and I'm deriving the specific nodes from it. In the code below, I've included only a few derived classes. Building the tree (randomly) is no problem. However, I'm looking for a clever way to evaluate the tree. I think that uncommenting the lines in bold print would in principle do it. However, this is not possible because "value" is not a member of the base class. The type of "value" is different in the derived classes, so I cannot simply declare it in the base class.
"Node.h"
#pragma once
class NodeBase{
public:
NodeBase* Child_1;
NodeBase* Child_2;
virtual void evaluate() = 0;
[Code] ....
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Dec 3, 2014
A have two classes, one inheriting the other, and the parent class being abstract (I plan on adding more child classes in the future). For reasons I won't bother mentioning, I'm making use of an STL container as a way for me to access all of the child objects in the heap. I've done so by making use of a map, with key type int and value type being a pointer to the parent class:
//PARENT.H
class Parent {
protected:
static int n;
static std::map<int, Parent*> map;
public:
virtual void pureVirtual() = 0;
[code]....
The Problem:In line 5 of Parent.cpp, initializing the value of the element to new Child won't work, as according to the compiler, the Child class hasn't been declared yet, and including Child.h into the Parent.h only opens an even bigger can of worms.I also can't initialize it as new Parent, seeing as the parent class is an abstract one.
The Question:Is there a way I can initialize the static map properly. Making the Parent class abstract is not an option.
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Jul 11, 2012
For example, in a header file A.h, I define an abstract class,
Code:
// A.h
class A {
public:
virtual void foo() = 0;
private:
static int _x;
};
How'd I initialize static member data _x?Normally, we initialize a static member data in a cpp file. However, there is not cpp file for A.h. If I intialize _x in header file, there will be linker errors like mulitple defined symbols. What is appropriate way to do that?
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Mar 6, 2014
The abstract class can provide more functionality without affecting child classes.If we add any method to the interface ,then will it affect all the child classes ?
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Jul 31, 2014
I want to develop an application which can host multiple views of explorer (window), where as each window is totally separate from others. So that I can have multiple desktop views through my single explorer. Any built in feature in .NET ?
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