problem using std::copy

[BillMoo]

Hello,

I have a pointer to an array of doubles that is 2448 in size. I can easily traverse this array and output any or all of the values using pointer arithmetic.

But I wanted to make use of the std::copy(...) to extract columns of values from this array so I can work on them.

std::vector < double > db = std::vector < double >(48, 99.9) ;
for (r = 0; r < 51; r++)
{
    std::copy(m_Data + (r + 48), m_Data + 2448, db.begin()) ;
    for (std::vector < double >::const_iterator ci = db.cbegin(); ci != db.cend(); ci++)
    {
        qDebug() << "Value" << *ci ;
    }
}
qDebug() << "Done" ;

Now this code, extracted from the apply() function works as expected but has the undesired side effect of terminating my application! I see the data and the "Done" text appear in the console however I never see my "Success" or "Failure" message appear when I execute:

if (bp->apply())
{
        qDebug() << "Success" << id ;
}
else
{
	qDebug() << "Failure" ;
}

I can only assume it is something I am doing wrong but to be honest I cannot see what or where it is, so I would really appreciate your comments on this please.

--
Bill

[ashishkumar]

I guess this has nothing to do with the array or std::copy or vector. It's all about qDebug() and bp->apply(). Are you seeing the Success and Failure after you comment out this vector /array/std::copy related code??

[Galik]

I think you have your maths wrong for the pointer arithmetic:

std::copy(m_Data + (r * 48), m_Data + (r * 48) + 48, db.begin());

[BillMoo]

Thank you for the replies. The answer was in fact the math as pointed out by Galik, so thank you very much for that. So back to School for me I guess! Thanks again.

--
Bill

[ashishkumar]

I guess that the wrong math leading to some exception being thrown and the conditional if/else was not being hit.

[jsmith]

Also, if you are going to use db.begin() as the OutputIterator (last parameter to std::copy), you need to ensure that the vector is large enough to hold all the elements you're about to copy over because the vector will not be resized.