Fastest way to reset a value in every struct element of a vector?

Question

Very much like this question, except that instead vector<int> I have vector<struct myType>.

If I want to reset (or for that matter, set to some value) myType.myVar for every element in the vector, what's the most efficient method?

Right now I'm iterating through:

for(int i=0; i<myVec.size(); i++) myVec.at(i).myVar = 0;

But since vectors are guaranteed to be stored contiguously, there's surely a better way?

Answer 1

Resetting will need to traverse every element of the vector, so it will need at least O(n) complexity. Your current algorithm takes O(n).

In this particular case you can use operator[] instead of at (that might throw an exception). But I doubt that's the bottleneck of your application.

On this note you should probably use std::fill:

std::fill(myVec.begin(), myVec.end(), 0);

But unless you want to go byte level and set a chunk of memory to 0, which will not only cause you headaches but will also make you lose portability in most cases, there's nothing to improve here.