从向量中提取值

Question

I am trying to extract a set of points from a vector and do computation on them. The points are stored like

std::vector<Vector> m_points1;
m_points1.push_back(Vector( -4.0, 8.0));
m_points1.push_back(Vector( -1.0, -7.0));
m_points1.push_back(Vector( 0.0, -8.0));
m_points1.push_back(Vector( 2.0, -4.0));
m_points1.push_back(Vector( 3.0, 1.0));

I can't loop through it as I used to do with arrays and get the values I want. My code looks likes:

for(std::vector<Vector>::iterator i=points.begin();i != points.end();i++)
{
    k=i;
    for(std::vector<Vector>::iterator j=points.begin();j != points.end();j++)
    {
        if(k==j)
        {
            continue;
        }
        else
        {
                //How to get values ???
        }

    } 

}

How can i extract the points? and do computations on only x coordinates ?

Answer 1

You can use range-based for loops and avoid the iterators all together.

for (auto const& ptA : points)
{
    for (auto const& ptB : points)
    {
        if (&ptA == &ptB)
        {
            continue;
        }
        else
        {
            // directly use ptA and ptB
        }
    }
}

If you are unable to use C++11, you can do the following in your else block

        else
        {
            Vector const& ptA = *i;
            Vector const& ptB = *j;
        }

Depending on your implementation of Vector you would then do something like

double width = ptA.x - ptB.x;

Answer 2

I figured it out. So i will write just a simple example

for(unsigned int i = 0 ; i<points.size() ; i++)
{
       temp = points[i](0);
}

to loop through a vector it needed an unsigned iterator, and to access just one of the elements u have to access it with (x) where x determines which element. in this question 0 is the x-coordinates

Answer 3

else
{
    // do wathever you want using
    // i->x
    // i->y
    // j->x
    // j->y
    float dist = sqrt( (i->x-j->x)*(i->x-j->x)
                     + (i->y-j->y)*(i->y-j->y) );
}