Question

it’s a weird problem that I have
I have a very simple constructor that’s creates a matrix with no values:

RegMatrix::RegMatrix(const int numRow, const int numCol):
    _numRow(numRow),_numCol(numCol),_matrix()
{

}

_matrix is a vector that holds ‘Comlex’, an object I’ve created

and VAL(i,j) is #define VAL(i,j) ((i * _numCol) + j)

Now, I call this constructor in function transpose:

RegMatrix RegMatrix::transpose()
{
    RegMatrix newMatrix(_numCol,_numRow);
    cout << "DIMENSIONS " << newMatrix._numRow << " " << newMatrix._numCol << endl;
    for(int j=0; j<_numCol; j++)
    {
        for(int i=0; i<_numRow; i++)
        {
            newMatrix._matrix[VAL(i,j)] = _matrix[VAL(j,i)]; //<--SEGMENTATION FAULT
        }
    }
    return newMatrix;
}

And here’s my problem: I get a segmentation fault the very first time I enter the second loop. When I use the eclipse debugger I see that _nunRow and _numCol values of newMatrix seem to be garbage (one is ‘0’ the other is -10000000 or something like that). What’s even more weird is that I added the output line just to be sure and it gave me the right numbers!
So, any ideas as to what can be my problem?
Thanks!

Answer 1

You are indexing into an empty vector, which is doomed to fail. Use at instead of the subscript operator and you will get an exception.