C++ unordered_maps vs Go map benchmark

maps.cpp

#include <unordered_map> 
#include <string> 
#include <vector> 
const int numOfStrings = 100000; 
const int numOfIterations = 1000; 

// adapted from: https://medium.com/@griffinish/c-and-golang-neck-and-neck-on-maps-e7867adfadc6
// g++ -std=c++0x -O3 -o maps_cxx maps.cpp
//
// time ./maps_cxx
// 
// real    0m18.676s
// user    0m16.818s
// sys     0m1.858s
//
// g++ (Ubuntu 4.8.4-2ubuntu1~14.04.4) 4.8.4

int main() { 
  // First make list of numeric strings 
  // This should be one relatively cheap 
  // loop. The container holds string 
  // representations of integers. 
  std::vector<std::string> numStrings; 
  numStrings.reserve(numOfStrings);
  for (auto i=0; i<numOfStrings; i++) {
      numStrings.push_back(std::to_string(i)) ; 
  } 
  // Check insert speed, 10 million inserts in total 
  for (auto i=0; i<numOfIterations; i++){ 
     std::unordered_map<std::string,int> strToInt; 
     strToInt.reserve(numOfStrings);
     for (auto& item : numStrings){ 
         strToInt[item] = item.size(); 
     } 
  }
  return 0;
}

maps.go

package main

// adapted from: https://medium.com/@griffinish/c-and-golang-neck-and-neck-on-maps-e7867adfadc6
// go build maps.go
//
// time ./maps
//
// real    0m7.775s
// user    0m9.900s
// sys     0m0.088s
//
// go version go1.12 linux/amd64

import "fmt"

const numOfStrings = 100000
const numOfIterations = 1000

func main() {
	// First make list of numeric strings
	// This should be one relatively cheap
	// loop. The container holds string
	// representations of numbers.
	numStrings := make([]string, 0, numOfStrings)
	for i := 0; i < numOfStrings; i++ {
		numStrings = append(numStrings, fmt.Sprint(i))
	}
	for i := 0; i < numOfIterations; i++ {
		strToInt := make(map[string]int, numOfStrings)
		for _, item := range numStrings {
			strToInt[item] = len(item)
		}
	}
}