C++ :: Class Definitions Have Interwoven Dependency
Mar 29, 2013
I have an exercise from my text that defines a StrBlob class, then a StrBlobPtr class to hold weak pointers to the StrBlobs. This is from C++ Primer (5th Edition) and coincidentally, the entire chapter is available on-line at here.
My problem is that the begin and end functions of StrBlob can't be defined until the entire StrBlobPtr class is defined. Forward declarations don't cut it, since begin and end need more than pointers.
The solution (if you also look at the errata for the book) seems to be to define StrBlob, leave begin and end undefined, then full define StrBlobPtr, and following that, finally define StrBlob::begin() and StrBlob::end().
Anyhow, the above works, as I show in the included code below - but it seems like a hack and messy. What would be the proper way to do this? My text may be obfuscating the issue in the pursuit of pedagogy.
Additionally, how would one separate StrBlob and StrBlobPtr into there own headers? I'd think it impossible, since the StrBlob would have to nestle an "#include "StrBlobPtr.hpp" in the center of it's own definition...?
Today I faced a problem where I had circular dependency in my template arguments. I was trying to make a class hierarchy similar to:
template<class BType> class A_base { public: BType* getB(); };
[Code] .....
Basically I had objects that were of type A<B<A<B<...
Basically I have a tree like structure of heterogeneous types that must facilitate two-way interactions where A's can call B's and B's can call A's. This structure is useful in many contexts the difference is the methods A and B provide are different in each of these contexts. Instead of adding the getA and getB and all the other connectivity methods in every version of A and every version of B, I wanted to create a base class that managed this automatically.
Another piece of advice was break up your code so there is a forward-only and backwards-only dependent types. This is not a complete solution because the two cannot know about the other and this does not really facilitate arbitrary two-way communication (where A calls B then B calls A back). It also makes the code more complicated in that I have two sets of objects and interfaces.
So the solution was to make the template arguments specific to the things I wanted to be flexible. The connectivity interface of A_base and B_base should be constant. Hence that cannot be in the template parameter. It was merely the traits that I wanted to make flexible so... I came up with this solution:
#include <iostream> template<class aTraitType,class bTraitType> class A; template<class aTraitType,class bTraitType> class B;
[Code] ....
Now this compiles and works great. The problem is that aObj and bObj cannot call their opposite within a trait method because print() does not know anything about the connectivity. So the solution there was to make traits an abstract base class. Then magically everything works!
#include <iostream> template<class aTraitType,class bTraitType> class A_base; template<class aTraitType,class bTraitType> class B_base;
[Code] .....
So this outputs the following. Clearly there is two-way communication!
Class A is not connected to B Class B is not connected to A Class A at 0x7fff25d1aa10 reporting for duty Class B at 0x7fff25d1aa00 reporting for duty Class B at 0x7fff25d1aa00 reporting for duty Class A at 0x7fff25d1aa10 reporting for duty Class A at 0x7fff25d1aa10 reporting for duty Class B at 0x7fff25d1aa00 reporting for duty
I have function that returns historical data. I can access it, using file name. If I use file name, it reads that file and saves it to dictionary, so that in the future, if historical data is required for the same file, it does not read it again (it's lazy loading). If no file is supplied to the function, it tries to read file which is given in app settings.
However, for unit testing, I do not want to read any file. Instead, I want it to use small sample of hardcoded historical data. In order to do that, I think, I need to introduce interface to it. Then I can use some IoC to choose between different implementation for unit testing purpose and ordinary launch of application.
Function to get history is given as follows:
public static class Auxiliary { private static Dictionary<string, MyData> _myData; public static MyData GetData(string fileName = null) { // ... } }
I have created default Unit Test project with Visual Studio so, as far as I know, by default it uses MSTest as test runner and MSUnit as unit testing framework but it does not have any IoC container so I should manage NuGet packages for solution and install Unity.
As far as I know, MSUnit (aka Moles) can unit test static methods (it's unconstrained isolation framework, like Typemock Isolator, unlike NUnit) but still many people suggest not to use any static methods for unit testing.
Should I use shim or stub [URL] Stubs should be used for faking external dependencies and here it is not external library, but my own code.
I was trying to make this program using function and everything seemed to be going great....until I compiled. This is just a project I want to work on myself. It's going to be more than what it is now.
I received next errors:
Compiling... 700Dlg.cpp E:CPP700700Dlg.cpp(65) : error C2601: 'KeyEvent' : local function definitions are illegal E:CPP700700Dlg.cpp(106) : error C2601: 'MsgLoop' : local function definitions are illegal E:CPP700700Dlg.cpp(115) : error C2601: 'KeyLogger' : local function definitions are illegal E:CPP700700Dlg.cpp(142) : error C2601: 'main' : local function definitions are illegal Error executing cl.exe.
[Code] .....
I need load keylogger code by MFC Dialog. How I can do it ?
I am using a library X that has functions x,y,z plus some others. also i am using a library Y that has those same functions (x,y,z) plus some others. (so both libraries have certain objects that are shared). libraries are designed to do different things and i need them both . However when i load them both i get
sem.c.text+0x2c10): multiple definition of `upper' ...
errors.
libraries are big and rewriting is not an option for me. Question: how do i bypass this problem?
When I try to compile a single file with GCC (I'm using Code::Blocks as my IDE if that is relevant) it gives me a bunch of undefined reference errors. Well, of course they are undefined since I haven't linked anything yet, but why is GCC complaining at compiling time?
The problem is that when I try to link and compile the project in one go I don't get any errors. The references in question are from the GLEW library if that is relevant.
srccharrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewDeleteBuffers'| srccharrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewDeleteBuffers'| srccharrenderer.o:charrenderer.cpp|| undefined reference to `glEnableClientState@4'| srccharrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewBindBuffer'| srccharrenderer.o:charrenderer.cpp|| undefined reference to `glVertexPointer@16'|
Say in my main class, I have a function fight(Player p1, Player p2) and I would like to do something like this in the fight function, given that p1 is the human and p2 is the computer:
//function fight() fight(Player p1, Player p2) { p1.func2(); } //using function fight() fight(human, computer);
When I compile the program, I got this: error: ‘class Player’ has no member named 'func2()' What can I do to allow p1 to call func2 inside fight()? I'm not allowed to use pointers as the parameter for fight() and have to use the signature fight(Player p1, Player p2).
The compiler creates virtual table for the base class and also for the derived class whether we override it or not.
That means each class has separate virtual table. when we get the size of the each class with out any data members... the size of base is -- 4 bytes(64 bit) and the size of derived is -- 1
The size of base class 4 is correct since it creates the virtual pointer internally and its size is member data + virtual pointer, but it in this case I have included any data members so it has given 4 byts.
But why in case of derived is 1 byte, since it the derived class has overridden the virtual function from base, this will also contains the virtual pointer which will be pointing to derived class Vtable, it the size of the class suppose to be 4 instead of 1 byte.
#include <iostream> #include "curve1.h" #include "curve2.h" using namespace std; int main() { Curve1 curve1Obj; Curve2 curve2Obj;
[Code]...
Base class Score has two derived classes Curve1 and Curve2. There are two curve() functions, one is in Curve1 and other in Curve2 classes. getSize() returns the value of iSize.
My base class header score.h looks like this:
#ifndef SCORE_H #define SCORE_H class Score { private: int *ipScore; float fAverage; int iSize;
[Code]...
You can see that I have used curve1Obj to enter scores, calculate average and output. So if I call getSize() function with cuve1Obj, it gives the right size that I took from user in enterScores() function. Also the result is same if I call getSize() in score.cpp definition file in any of the functions (obviously). .....
The problem is when I call curve() function of Curve2 class in main (line 23) with the object curve2Obj, it creates a new set of ipScore, fAverage and iSize (i think?) with garbage values. So when I call getSize() in curve() definition in curve2.cpp, it outputs the garbage. .....
How can I cause it to return the old values that are set in curve1.cpp?
Here is my curve2.cpp
#include <iostream> #include "curve2.h" using namespace std; void Curve2::curve() { cout << "getSize() returns: " << getSize() << endl; // out comes the garbage }
Can I use a function to simply put values from old to new variables? If yes then how?
Code: Error1error LNK2019: unresolved external symbol "public: __thiscall ReachTop<class Character>::ReachTop<class Character>(class Character *)" (??0?$ReachTop@VCharacter@@@@QAE@PAVCharacter@@@Z) referenced in function "void __cdecl `dynamic initializer for 'gReachTop''(void)" (??__EgReachTop@@YAXXZ)Main.objDecisionTest
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?
#include <iostream> using namespace std; class superclass; class subclass1; class subclass2;
[Code] ....
As you can see I want to create a dynamically allocated storage of references to a parent class each of which can then point to a child class, how ever I do not know how to extract the child class out again from that array so i may access its variable b.
Let's say I have a Car object , and it contains inner Engine object.
Code: struct Car{ Engine mEngine; };
In order to initialize the engine object NOT by the default constructor (if it has any) , we use initialization semantics:
Code: Car::Car: mEngin(arg1,arg2,...) { other stuff here }
Now it gets tricky: Let's say a Car objects has 10 inner objects, each object has about 5 variables in it . Car is a base class for , e.g. , Toyota class. you don't want the Car class to have a constructor with 50 arguments. Can the inner objects of Car be initialized from the base class , e.g. Toyota?
Code: class Toyota: Car(...), mEngine(...), mGear(..) { ... };
The other options are: 1) like said , create a Car constructor which gets 50 arguments, then initialize Car as whole from Toyota - the code becomes less readable and less intuitive 2) Car constructor which get built-objects as arguments and initialize the inner objects with copy constructor . the code gets more readable but then you create many excess objects .
So I have a base class, lets call it base. In base I have a virtual function called update(), update just couts "base" then I have a class derived from base called derived;
it has a function called update(), update just couts "derived" then I create a vector called Vec it's initialised like this:
std::vector<base> Vec;
then I add an element into it like this
Derived DerElement; Vec.push_back(DerElement);
then when I type:
for (int i=0; i<Vec.size(); i++) { Vec.at(i).Update(); }
It outputs:
Derived DerElement2; DerElement2.Update();
and it outputs this:
#include <iostream> #include <vector> class Base { public: virtual void Update() {
