Question

In terms of performance, what would work faster? Is there a difference? Is it platform dependent?

//1. Using vector<string>::iterator: vector<string> vs = GetVector();  for(vector<string>::iterator it = vs.begin(); it != vs.end(); ++it) {    *it = 'Am I faster?'; }  //2. Using size_t index: for(size_t i = 0; i < vs.size(); ++i) {    //One option:    vs.at(i) = 'Am I faster?';    //Another option:    vs[i] = 'Am I faster?'; } 

Answer 1

Why not write a test and find out?

Edit: My bad – I thought I was timing the optimised version but wasn’t. On my machine, compiled with g++ -O2, the iterator version is slightly slower than the operator[] version, but probably not significantly so.

#include <vector> #include <iostream> #include <ctime> using namespace std;  int main() {     const int BIG = 20000000;     vector <int> v;     for ( int i = 0; i < BIG; i++ ) {         v.push_back( i );     }      int now = time(0);     cout << 'start' << endl;     int n = 0;     for(vector<int>::iterator it = v.begin(); it != v.end(); ++it) {         n += *it;     }      cout << time(0) - now << endl;     now = time(0);     for(size_t i = 0; i < v.size(); ++i) {         n += v[i];     }     cout << time(0) - now << endl;      return n != 0; }