Re: How to return a reference, when I really need it

From:

Jerry Coffin <jerryvcoffin@yahoo.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 31 Jul 2009 10:10:04 -0600

Message-ID:

<MPG.24dcc54b3667b641989722@news.sunsite.dk>

In article <2b75b844-4704-44f3-a186-8dc382293544@
24g2000yqm.googlegroups.com>, blacklight86@gmail.com says...

Hi,

I'm actually developing a tiny C++ library for managing linear algebra
operations, but I have a problem in managing the reference to an
object as return value. This is the method I wrote:

Vector Matrix::operator[] (size_t i) throw() {
        if (i >= rows)
                throw InvalidMatrixIndexException();

        vector<float> row;

        for (int j=0; j < cols; j++)
                row.push_back(matrix[i][j]);

        return Vector(row);
}

If you're going to create and return a vector, why not at least do
something like:

Vector Matrix::operator[](size_t i) throw() {
    if (i>=rows)
        throw InvalidMatrixIndexException();

    std::vector<float> row(matrix[i][0], matrix[i][cols]);
    return Vector(row);
}

OTOH, you might also want to look at std::valarray and its
associates. You seem to be basically reinventing a lot of that.

--
    Later,
    Jerry.