Creating a map using struct members throws bad_alloc

Question

So I have a struct

struct float3
{
    float x, y, z;
};

and I am trying to create a function to take the x,y,z values and map them to keys 0, 1, 2 for their respective dimension. I wrote the code below but it throws a bad alloc_exception. It appears like I'm running out of memory.

KdTree::float2map(std::vector<float3>& data)
    {    
       std::vector<std::map<int, float> > m_pnts;
       int cnt = 0;
       for(int i = 0; i = data.size(); i++)
          {
             std::map<int, float> tmp;
             tmp.insert(std::make_pair(0, data[i].x));
             tmp.insert(std::make_pair(1, data[i].y));
             tmp.insert(std::make_pair(2, data[i].z));

             m_pnts.push_back(tmp);
             std::cout << m_pnts.size() << std::endl;
            }

       }

       return m_pnts;
    }

I'm still fairly new to C++ so I'm sure there are many other ways to do this or to optimize this approach. The problem is I have to do this one 33,914,095 float3s and I can't think of another way to achieve this. Any help would be greatly appreciated.

Answer 1

Look at this line of code:

for(int i = 0; i = data.size(); i++)

You are setting i to data.size() in the condition of the for statement. This will cause an out of bounds access because data.size() will become the index to data vector whose elements are indexed from 0 to data.size() - 1.

That was probably not your intention. Use a proper condition in the for loop. It should be:

for(int i = 0; i < data.size(); i++)

Or better still, use a range-based for loop which help in avoiding such bugs:

for(const auto& ele: data)
{
    std::map<int, float> tmp;
    tmp.insert(std::make_pair(0, ele.x));
    tmp.insert(std::make_pair(1, ele.y));
    tmp.insert(std::make_pair(2, ele.z));
    m_pnts.push_back(tmp);
    std::cout << m_pnts.size() << std::endl;
}