Question

There is a vector of vectors:

std::vector <std::vector <float> > VoV;
VoV.resize(num);   // num is determined at run-time
for (int i=0; i<num; ++i) {

    VoV[i].resize(3);   // initializing to zero
}

I want to set all three elements to zero after some manipulation. I mean, I know initially they will be set to zero however, their values will change after a while and I want to set them all zero again. So, is the following correct? Is it efficient and is there a better way?

std::fill(VoV.begin(), VoV.end(), 0.f);

Answer 1

There are many ways you can set all of the data to zero. The simplest is perhaps:

VoV = std::vector<std::vector<float> >(num, std::vector<float>(3, 0.));

Or,

std::fill(VoV.begin(), VoV.end(), std::vector<float>(3, 0.));

Or,

for(std::vector<float>& v : VoV)
  std::fill(v.begin(), v.end(), 0.);

Or even:

for(auto& v : Vov)
  for(auto& f : v)
    f = 0;

_{Note: I haven’t tested any of these.}