C++ TIMER - mjerenje trajanja izvršavanja programa

/*
TIMER :: http://bit.ly/cpp-timer
Pomoćni alat za mjerenje trajanja izvršavanja programa
Kompajlirati u timer.exe
---------------------------------------------------------
pozivati iz konzole na sljedeći način:

timer start
program-koji-testiramo.exe
timer

---------------------------------------------------------
ili u jednoj liniji:

timer start & program-koji-testiramo.exe & timer

---------------------------------------------------------
ili iz samog programa za mjerenje trajanja jednog dijela programa:

int main() {
  system("timer start");
  // neki dio programa, npr. petlja
  system("timer");
}
*/

#include <cstdlib>
#include <iostream>
#include <algorithm>
#include <sstream>
#include <string>


#ifdef WIN32
#include <Windows.h>
#else
#include <sys/time.h>
#include <ctime>
#endif

using namespace std;

/* Returns the amount of milliseconds elapsed since the UNIX epoch. Works on both
 * windows and linux. */

typedef long long int int64;
typedef unsigned long long int uint64;
typedef unsigned int uint;

int64 GetTimeMs64()
{
#ifdef WIN32
 /* Windows */
 FILETIME ft;
 LARGE_INTEGER li;

 /* Get the amount of 100 nano seconds intervals elapsed since January 1, 1601 (UTC) and copy it
  * to a LARGE_INTEGER structure. */
 GetSystemTimeAsFileTime(&ft);
 li.LowPart = ft.dwLowDateTime;
 li.HighPart = ft.dwHighDateTime;

 uint64 ret = li.QuadPart;
 ret -= 116444736000000000LL; /* Convert from file time to UNIX epoch time. */
 ret /= 10000; /* From 100 nano seconds (10^-7) to 1 millisecond (10^-3) intervals */

 return ret;
#else
 /* Linux */
 struct timeval tv;

 gettimeofday(&tv, NULL);

 uint ret = tv.tv_usec;
 /* Convert from micro seconds (10^-6) to milliseconds (10^-3) */
 ret /= 1000;

 /* Adds the seconds (10^0) after converting them to milliseconds (10^-3) */
 ret += (tv.tv_sec * 1000);

 return ret;
#endif
}

string int2string(int64 i) {
   stringstream ss;//create a stringstream
   ss << i;//add number to the stream
   return ss.str();//return a string with the contents of the stream
}

int64 string2int(string s) {
    stringstream ss;//create a stringstream
    ss << s;
    int64 out;
    ss >> out;
    return out;
}


#include <iostream>
#include <fstream>

string readfile()
{
    fstream fin;
    string word;
    string testfile = "timer.txt";
    fin.open(testfile.c_str(), ios::in);
    if (fin.is_open()) {
        std::getline(fin, word, ' ');
        return word;
    }
    return "";
}

void writefile(string x) {
    ofstream fout;
    string word;
    string testfile = "timer.txt";
    fout.open(testfile.c_str(), ios::out);
    if (fout.is_open()) {
        fout << x;
    }

}

int main(int argc, char **argv) {

    if (argc >1) {
       string x = string(argv[1]);
       if (x == "start") {
            writefile(int2string(GetTimeMs64()));
       }
    } else {
        int64 starttime = string2int(readfile());
        cout << "Execution took " << (GetTimeMs64() - starttime) << " ms" << endl;
    }

}