string_generator.cc

/*
 * my result as follow : 
### O0:
$ g++ -std=c++11 string_generator.cc -o string_generator -O0  && ./string_generator
final val is :first_strsecond_strthird_str
Method 0 : 614.236 ms.
final val is :first_strsecond_strthird_str
Method 1 : 579.361 ms.
final val is :first_strsecond_strthird_str
Method 2 : 2782.47 ms.
final val is :first_strsecond_strthird_str
Method 3 : 3426.62 ms.

### O1:
final val is :first_strsecond_strthird_str
Method 0 : 551.289 ms.
final val is :first_strsecond_strthird_str
Method 1 : 558.395 ms.
final val is :first_strsecond_strthird_str
Method 2 : 1960.56 ms.
final val is :first_strsecond_strthird_str
Method 3 : 1673.75 ms.

### O3:
final val is :first_strsecond_strthird_str
Method 0 : 591.475 ms.
final val is :first_strsecond_strthird_str
Method 1 : 571.774 ms.
final val is :first_strsecond_strthird_str
Method 2 : 1655.44 ms.
final val is :first_strsecond_strthird_str
Method 3 : 1551.27 ms.

### O10:
final val is :first_strsecond_strthird_str
Method 0 : 580.474 ms.
final val is :first_strsecond_strthird_str
Method 1 : 570.846 ms.
final val is :first_strsecond_strthird_str
Method 2 : 1771.07 ms.
final val is :first_strsecond_strthird_str
Method 3 : 1504.82 ms.

$uname -a
Darwin yu.local 14.0.0 Darwin Kernel Version 14.0.0: Fri Sep 19 00:26:44 PDT 2014; root:xnu-2782.1.97~2/RELEASE_X86_64 x86_64
*/
#include <chrono>
#include <iostream>
#include <string>
#include <sstream>

#define REPEAT_COUNT 10000000

typedef std::chrono::high_resolution_clock hrclock;
typedef std::chrono::duration<double, std::milli> mil;
typedef std::chrono::duration<int64_t, std::ratio<1,1000000000>> nal;
typedef std::chrono::time_point<hrclock, nal> time_point;

std::string str_c0() {
    std::string some_str;
    for(int i = 0 ; i < REPEAT_COUNT ; i++) {
        some_str = "";
        some_str += "first_str";
        some_str += "second_str";
        some_str += "third_str";
    }
    return some_str;
}

std::string str_c1() {
    std::string some_str;
    for(int i = 0 ; i < REPEAT_COUNT ; i++) {
        some_str = "";
        some_str.append("first_str").append("second_str").append("third_str");
    }
    return some_str;
}

std::string str_c2() {
    std::string some_str;
    for(int i = 0 ; i < REPEAT_COUNT ; i++) {
        some_str = "";
        some_str = some_str + "first_str" + "second_str" + "third_str";
    }
    return some_str;
}

std::string str_c3() {
    std::stringstream some_sstr;
    for(int i = 0 ; i < REPEAT_COUNT ; i++) {
        //some_sstr = std::stringstream("first_str"); // this method even more costly
        some_sstr.str("");
        some_sstr << "first_str" << "second_str" << "third_str";
    }
    return some_sstr.str();
}

double tc_cnter(std::string (* str_cs)(void)) {
    time_point t0 = hrclock::now();
    std::string final_val = str_cs();
    time_point t1 = hrclock::now();
    std::cout << "final val is :" << final_val << std::endl;
    return mil(t1-t0).count();
}

int main(int argc, char * argv[]) {
    double ms = tc_cnter(str_c0);
    std::cout << "Method 0 : " << ms << " ms." << std::endl;
    ms = tc_cnter(str_c1);
    std::cout << "Method 1 : " << ms << " ms." << std::endl;
    ms = tc_cnter(str_c2);
    std::cout << "Method 2 : " << ms << " ms." << std::endl;
    ms = tc_cnter(str_c3);
    std::cout << "Method 3 : " << ms << " ms." << std::endl;
    return 0;
}