Comparison between std::transform vs. std::for_each (with boost::bind)

stbb_vs_sfbb.cxx

#include <iostream>
#include <cstring>
#include <vector>
#include <string>
#include <boost/bind.hpp>
#include <boost/ref.hpp>
#include <random>

using namespace std;
typedef std::vector<std::pair<std::string, int>> pair_vector;

class StringLengthCalculator{
public:
     void calc_length1(std::string* s){
        _size.push_back(std::pair<std::string,int>(*s,s->length()));
    }
     int calc_length2(std::string* s){
        return s->length();
    }
     pair_vector get_result(){
        return _size;
    }
     void pp(std::pair<std::string,int> s){
        std::cout << s.first << " => " << s.second << std::endl;
    }
private:
    pair_vector _size;
    int i = 0;
};



std::random_device rd;
std::mt19937_64 gen(rd()); //mersenne twister
std::string make_string(int length, std::uniform_int_distribution<int>& d){
    std::string t;
    //cout << "L:" << length << endl;
    for(int i = 96; i < length ; ++i){
        //(96,122]
        t += char(d(gen));
    }
    return t;
}

int main (int argc, char* argv[]) {
    const int ELEMENT_SIZE = atol(argv[1]);
    cout << "element size: " << ELEMENT_SIZE << endl;
    StringLengthCalculator s;
    std::vector <std::string*> vec_nums;
    double rn;
    std::uniform_int_distribution<int> d(97, 122);
    std::string ss;
    for(int i = 0; i < ELEMENT_SIZE; ++i){
        //Create a random string of random length
        //Fetch a random number
        rn = d(gen); 
        //Construct a string of length "rn"
        ss = make_string(rn, d);
        vec_nums.push_back ( new std::string(ss.c_str()) );    
    }
    //cout << "vec_nums size: " << vec_nums.size() << endl;
    
    if (strncmp(argv[2],"sfbb",4) == 0){
        std::cout << "std::for_each / boost::bind / implicit looping method\n=======================================" \
                    << std::endl;
        std::for_each(vec_nums.begin(), vec_nums.end(), boost::bind(&StringLengthCalculator::calc_length1, boost::ref(s), _1));
        pair_vector moo = s.get_result();
        std::for_each(moo.begin(), moo.end(), boost::bind(&StringLengthCalculator::pp, boost::ref(s), _1));
        cout << "size: " << moo.size() << endl;
    }
    else if (strncmp(argv[2], "stbb",4) == 0){
        std::cout << "std::transform / boost::bind / explicit looping method\n=======================================" \
                    << std::endl;
        vector<int> lengths ( vec_nums.size() );
        std::transform (vec_nums.begin(), vec_nums.end(), lengths.begin(), boost::bind(&StringLengthCalculator::calc_length2, boost::ref(s),_1) );
        for (int i=0; i<(signed int)vec_nums.size(); i++) {
            std::cout << *vec_nums[i] << " => " << lengths[i] << endl;
        }
        cout << "size: " << lengths.size() << endl;
    }
    return 0;
}