returning objects, not all members are copied?

[Luis G]

The template declaration:

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;
};

Problem when calling the function:

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:

	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:

0
1
2
3

-33686019 0 0 0

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?

[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.

[Luis G]

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.

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.

[Axter]

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.

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:

 
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;
} 

[Luis G]

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