returning objects, not all members are copied?

The template declaration:

Code:

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template<class TG> class CMatriz 
{
public:
        CMatriz(unsigned int j,unsigned int k=1);
        ~CMatriz();
        CMatriz<TG> T(void);
        void inserta(unsigned int j,unsigned int k,const TG &op);
        TG obten(unsigned int j,unsigned int k) const;
        CMatriz<TG> operator=(const CMatriz<TG> &op);
        friend ostream &operator<<(ostream &os,const CMatriz<TG> &op);
protected:
        void Destruye();
        void Crea(unsigned int j,unsigned int k);
        unsigned int m_reng,m_cols;
        vector<TG> m_matriz;
};

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Problem when calling the function:

Code:

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template<class TG>
CMatriz<TG> CMatriz<TG>::T(void)
{
        unsigned int i,j;
        CMatriz<TG> transpuesta(m_cols,m_reng);
        for(i=0;i<m_reng;i++)
                for(j=0;j<m_cols;j++)
                        transpuesta.inserta(j,i,obten(i,j));

        return transpuesta;
}

---

Code executed:

Code:

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        CMatriz<int> matriz(4),matriz2(2);

        matriz.inserta(0,0,0);
        matriz.inserta(1,0,1);
        matriz.inserta(2,0,2);
        matriz.inserta(3,0,3);
        cout << matriz;
        cout << matriz.T();

---

the output is:

Quote:

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0
1
2
3

-33686019 0 0 0

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The output I'm expecting is "0 1 2 3" (I do get this output if I do cout << transpuesta within CMatriz<TG>::T(void) right before return transpuesta)

The object put in place of matriz.T() is supposed to be a copy of transpuesta but m_matriz is not being copied.
Note: ~CMatriz() is empty.


Any hints?

You're passing CMatriz back by value, but you don't have a copy constructor.

You should add a copy constructor to class CMatriz.

Also, I don't recommend passing by value. It's not efficient for a matirx class to be pass by value.

Quote:

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Originally Posted by Axter

You're passing CMatriz back by value, but you don't have a copy constructor.

You should add a copy constructor to class CMatriz.

Also, I don't recommend passing by value. It's not efficient for a matirx class to be pass by value.

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Thanks for the quick reply.
I'm researching as to how to do a copy constructor, it's been a while since I did some basic programming in C++ and I don't remember ever coming into that.

To make it efficient how should I do it?
I want to be able to write expressions like:
A = A*B.T()+2.0;

Thanks again.

Quote:

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Originally Posted by Luis G

To make it efficient how should I do it?
I want to be able to write expressions like:
A = A*B.T()+2.0;
Thanks again.

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If you want to use the above syntax, that does make it hard to avoid passing by value.
However, I recommend you pass by value in your operators.
Example:

PHP Code:

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template<class TG>
CMatriz<TG> operator*(const CMatriz<TG>& left_,const CMatriz<TG>& right_)
{
  CMatriz<TG> Tmp;
  //Code here to add left and right to Tmp
    return Tmp;
}

template<class TG>
CMatriz<TG> operator+(const CMatriz<TG>& left_,const CMatriz<TG>& right_)
{
  CMatriz<TG> Tmp;
  //Code here to add left and right to Tmp
    return Tmp;
} 


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Too bad there's no way (or easy way) to keep the natural syntax I want and make it efficient.

I was thinking I should implement those operators just as you suggested.

Thanks again for the help, it works properly now :)