Type conversion problem- C++

vivekr · 12-29-2005, 08:21 AM

Hi to all.

My problem lies in this statement

Code:

Weight=Weight+x;

where Matrix<float> Weight;
Matrix<int> x;

I have tried things like

Code:

Weight=Weight+(Matrix<float>) x;
Type cast:
operator Matrix<float> ()
	{
		Matrix<float> x(rows,columns);
		for(int i=0;i<rows;i++)
			for(int j=0;j<columns;j++)
				x.Array[i][j]=Array[i][j];
		return x;
	}

// not sure about the correctness of this thing

Please help me. Expecting quick responses.
Thanks to all the hearts that care to help me.

dmail · 12-29-2005, 08:31 AM

I take it you have overloaded the addition and assignment operators.

vivekr · 12-29-2005, 09:38 AM

yes i have...

Code:

template <class Type>
Matrix<Type> :: Matrix(Matrix &matrix)
{
	rows = matrix.rows;
	columns = matrix.columns;
	Array=new Type* [rows];
	for(int i=0;i<rows;i++)
		Array[i]=new Type[columns];
	for(i=0;i<rows;i++)
		for(int j=0;j<columns;j++)
			Array[i][j]=matrix.Array[i][j];
}

template<class Type>
void Matrix<Type> :: operator =(Matrix<Type> &matrix)
{
	if(rows != matrix.rows || columns != matrix.columns)
	{
		cerr<<" Order mismatch";
		exit(1);
	}

	for(int i=0;i<rows;i++)
		for(int j=0;j<columns;j++)
			Array[i][j]=matrix.Array[i][j];
}

template<class Type>
Matrix<Type> operator + (Matrix<Type> &matrix)
{
	if(rows != matrix.rows || columns != matrix.columns)
	{
		cerr<<" Order mismatch";
		exit(1);
	}
	
	Matrix<Type> x(rows,columns);
	for(int i=0;i<rows;i++)
		for(int j=0;j<columns;j++)
			Array[i][j]=Array[i][j]+matrix.Array[i][j];
    return x;
}

------
Edit:
Error:
'type cast' : cannot convert from 'class Matrix<int>' to 'class Matrix<float>'
No constructor could take the source type, or constructor overload resolution was ambiguous

wonder why?

dmail · 12-29-2005, 11:54 AM

im not sure if im going along the correct lines of thought here but instead of

Code:

Weight=Weight+x;

where Matrix<float> Weight;
Matrix<int> x;

what happens when you do

Code:

x=Weight+x;

does that give you an error?

I'm not sure but i think the func

Code:

template<class Type>Matrix<Type> operator + (Matrix<Type> &matrix)

is returning a matrix of type int if the parameter is of type int.

you may need to do specialisation such as

Code:

(Matrix<int> &matrix)

then again i could be completly wrong

vivekr · 12-29-2005, 07:00 PM

Code:

template<class Type1,class Type2>
Matrix<Type1> Matrix<Type1>::operator + (Matrix<Type2> &matrix)
{
	if(rows != matrix.rows || columns != matrix.columns)
	{
		cerr<<" Order mismatch";
		exit(1);
	}
	
	Matrix<Type2> x(rows,columns);
	for(int i=0;i<rows;i++)
		for(int j=0;j<columns;j++)
			Array[i][j]=Array[i][j]+Type1(matrix.Array[i][j]);
    return x;
}

This pops up template function has already been defined
error.

As u said I tried to be specific by overloading for the float and int types alone.that too resulted in the same error.

And x=x+Weight -- too gave the same error.
I would love to send u the headerfile containing these operations if u want.
Please help...
Thanks to dmail for ur sincere contribution to sort me out of this...

dmail · 12-30-2005, 08:24 AM

Quote:

Originally Posted by vivekr

I would love to send u the headerfile containing these operations if u want.

sure bounce them over and i'll try and help

Code:

dmail00 at gmail.com

ta0kira · 12-31-2005, 03:47 AM

Try it this way:

Code:

template <class Type1>
struct Matrix
{
        template <class Type2>
                Matrix
        operator + (const Matrix <Type2>&);

        //...
};

template <class Type1> template <class Type2>
Matrix <Type1> Matrix <Type1> ::operator + (const Matrix <Type2> &matrix)
{
        //...
}

You have to separate the template declarations because the first is to open the scope of Matrix, and the second takes place within that scope.

Also, you should make your copy constructor, assignment operator, and + operator take a const Matrix; often times you will be given a const reference to copy, but if your operator doesn't take const it won't work. In other words, take references as const unless you can't do it otherwise.
ta0kira

vivekr · 01-02-2006, 10:10 AM

To ta0kira:
Your idea isn't working..
The second template definition is shown as an error

Code:

template <class Type>
class Matrix
{
....
template<class Type2>
Matrix<Type2> operator *  (Type2 value);
....
};

template<class Type> 
template<class Type2> 
Matrix<Type2> Matrix<Type> :: operator * (Type2 value)
{
	Matrix<Type2> x(rows,matrix.getColumns());

	for(int i=0;i<rows;i++)
		for(int j=0;j<matrix.columns;j++)
			x.Array[i][j]=Array[i][j]*value;		
	return x;
}

 Errors:
syntax error : ''template<''
'Type2' : undeclared identifier ....
template definitions cannot nest

To dmail:
Sure I will send my code by tomo.
I actually was discussing a situation where a type cast wasnt required. anyway i have found a problem and need to find a soln. So i will send it to u