Question

I have a 4d vector and I am trying to add values to it. I don’t receive any compiler errors, but when running it, the program freezes when it gets to the line where I am adding values to this vector.

I initialize the vector in a header file like this:

std::vector<std::vector<std::vector<std::vector<unsigned int> > > > _celllist;

The array is then sized with the following:

_celllist.resize(_vnx);
 for(int i=0;i<_vnx;i++) 
    {
        //y axis size
        _celllist[i].resize(_vny);
            for(int j=0;j<_vny;j++)
            {
                //z axis size
                _celllist[i][j].resize(_vnz);
            }
    }

This line then causes the program to crash:

_celllist[ix][iy][iz].push_back(i);

Note that ix, iy, and iz are all int and i is an unsigned int.

Can anyone see what might be going wrong here? Thanks

Answer 1

The operator[] does not expand or guarantee that the element is valid. It’s a faster version of at() with little or no error checking:

Convert your code to the safer version for now:

_celllist.at(ix).at(iy).at(iz).push_back(i);

This new code will throw an out_of_range exception if your indices are off.