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private: instance in class with in namespace Question


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#1 greenzone   Members   -  Reputation: 672

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Posted 26 April 2014 - 12:41 PM

I am having a problem with the use of a class member that does not seem to be constructed.

 

I have a name space called "DogActivity".

 

In this name space there are two classes " DogSounds and Bark".

 

In the Bark class I have a private: instance of DogSounds.

 

Now in the constructor of the DogSounds class there is a private: int variable called NumSounds that is initialized to 0.

 

 

 

The problem is if i create an instance of DogSound in my main program the constructor is called and the NumSounds variable is set to 0 as planned.

 

But

 

If i create an instance of Bark in the main program the constructor of DogSounds is never called and NumSounds is never initialized.

 

here is an example of my namespace with classes.

namespace DogActivity
{

    class DogSounds
    {
            public:
             DogSounds() { NumSonds = 0;}

            private:
               int NumSounds;
     };

     class Bark{

       private:
            DogSounds dogSounds;

     };

}

Now here is how i would use in main



using namespace DogActivity;

int main ( int argc, char * argv[] ) 
{

Bark bark;

// Do work with bark bellow

}

But when I create the instance of Bark the privat: dogSounds' variable "NumSounds" is never set to 0. The Constructor of dogSounds is never called, why is this? shouldn't the constructor of dogSounds be called as soon as i create an instance of Bark? what might i be doing wrong here?


Edited by greenzone, 26 April 2014 - 01:20 PM.

J-GREEN

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#2 exOfde   Members   -  Reputation: 810

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Posted 26 April 2014 - 01:11 PM

The member variable of DogSounds:

 

  • is Not a pointer.
    • Only pointer should be assign to NULL or since C++11 to nullptr.
  • NULL is not a Number.
    • in C NULL is just a #define for this: ((void*)0) 
    • in C++ can it be just a Zero but don't have to be from what i learned.
  • Here an link what NULL represent: http://www.cplusplus.com/reference/cstring/NULL/

 

Your code is also a bit wrong!!

 

Bark has a member Variable of type DogSounds!

but you never use this member. Instead you try to access NumSounds

which was never declared in the class Bark.

 

to access NumSounds from dogsounds you would need to do this:

dogSounds.NumSounds

but even that is not  possible because you set NumSounds in the class DogSounds private so it can never be accessed from the Outside. What you need to do is to write setter and getter for DogSounds to manipulate his member.


Edited by exOfde, 26 April 2014 - 01:21 PM.


#3 greenzone   Members   -  Reputation: 672

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Posted 26 April 2014 - 01:16 PM

Wait your right im sorry the null should be 0. but this does not change the fact that the constructor is not being called.


Edited by greenzone, 26 April 2014 - 01:18 PM.

J-GREEN

Greenpanoply

#4 nobodynews   Crossbones+   -  Reputation: 2112

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Posted 26 April 2014 - 01:17 PM

Copy-paste your actual code so it will be easier to figure out what's going on. I don't think anyone can determine what your code is doing without the code you're actually using.

C++: A Dialog | C++0x Features: Part1 (lambdas, auto, static_assert) , Part 2 (rvalue references) , Part 3 (decltype) | Write Games | Fix Your Timestep!


#5 greenzone   Members   -  Reputation: 672

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Posted 26 April 2014 - 01:33 PM

I have edited it so it will be just as basic as it could possibly be. What I am asking is, with the example shown above, Would the constructor of DogSounds be called if an instance of Bark was created?

 

I mean 2 classes in a names space.

 

class A and class B

 

class B has a private: instance of class A.

 

Assuming that the namespace is being used properly,  Would the constructor of class A be called when an instance is created of class B?


J-GREEN

Greenpanoply

#6 Aliii   Members   -  Reputation: 1448

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Posted 26 April 2014 - 01:33 PM

Did you copy-paste this code? Cause the variable name is "NumSonds" instead of "NumSounds".


Edited by Aliii, 26 April 2014 - 01:35 PM.


#7 greenzone   Members   -  Reputation: 672

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Posted 26 April 2014 - 01:37 PM

no i did not paste the code. its just pseudo coded that i made to elaborate. I am sorry i should have made note of that.

 

this is what i am actually actually asking

 

 

 

 

2 classes in a names space.

 

class A and class B

 

class B has a private: instance of class A.

 

Assuming that the namespace is being used properly,  Would the constructor of class A be called when an instance is created of class B?


J-GREEN

Greenpanoply

#8 Aliii   Members   -  Reputation: 1448

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Posted 26 April 2014 - 01:42 PM

Unless your compiler does something crazy optimization, it should be called.



#9 nobodynews   Crossbones+   -  Reputation: 2112

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Posted 26 April 2014 - 01:44 PM

I asked for your actual code because I knew it was psuedo-code. I knew that because what you posted shouldn't even compile. As for your question, namespaces shouldn't have any effect on whether a constructor is called or not. In the case where class B has an instance of class A then the constructor for A should be called. Since its not, you have a bug. We could help you find the bug if you'd paste your actual code.

C++: A Dialog | C++0x Features: Part1 (lambdas, auto, static_assert) , Part 2 (rvalue references) , Part 3 (decltype) | Write Games | Fix Your Timestep!


#10 greenzone   Members   -  Reputation: 672

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Posted 26 April 2014 - 01:49 PM

Thank you guys for the help and I do appreciate your being able to look past my wack psuedo-code. but thats all i needed to know. the constructor should be called :)


J-GREEN

Greenpanoply




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