C/C++ Datetime Format String Performance Tests

datetime_format_string.cpp

/*
Just compile with g++ datetime_format_string.cpp -std=c++11
Tested on GCC 5.4.0 on Ubuntu 16.04
*/

#include <iostream>
#include <chrono>

#include <sys/time.h>
#include <stdio.h>

using namespace std;
using namespace chrono;

void func1() {
    struct timeval current_time;
    gettimeofday(&current_time, 0);

    char time_str[128];
    strftime(time_str,
             sizeof(time_str),
             "%F %T", localtime(&current_time.tv_sec));

    cout << time_str << endl;
}

void func2() {
    struct timeval current_time;
    gettimeofday(&current_time, 0);

    char time_str_without_subseconds[128];
    strftime(time_str_without_subseconds,
             sizeof(time_str_without_subseconds),
             "%F %T.%%06ld", localtime(&current_time.tv_sec));

    char time_str[128];
    sprintf(time_str, time_str_without_subseconds,
            (long)current_time.tv_usec);

    cout << time_str << endl;
}


void func3() {
    struct timeval current_time;
    gettimeofday(&current_time, 0);

    struct tm local_tm;

    localtime_r(&current_time.tv_sec, &local_tm);

    char time_str[128];

    sprintf(time_str, "%04d-%02d-%02d %02d:%02d:%02d.%06ld",
         local_tm.tm_year+1900, local_tm.tm_mon+1,
         local_tm.tm_mday, local_tm.tm_hour, local_tm.tm_min,
         local_tm.tm_sec, (long)current_time.tv_usec);
    
    cout << time_str << endl;
}

int main() {
    high_resolution_clock::time_point t1 = high_resolution_clock::now();

    for(int i = 0; i < 1000000; i += 1) {
        func1();
    }

    high_resolution_clock::time_point t2 = high_resolution_clock::now();

    for(int i = 0; i < 1000000; i += 1) {
        func2();
    }

    high_resolution_clock::time_point t3 = high_resolution_clock::now();

    for(int i = 0; i < 1000000; i += 1) {
        func3();
    }

    high_resolution_clock::time_point t4 = high_resolution_clock::now();

    auto duration1 = duration_cast<milliseconds>( t2 - t1 ).count();
    auto duration2 = duration_cast<milliseconds>( t3 - t2 ).count();
    auto duration3 = duration_cast<milliseconds>( t4 - t3 ).count();

    cerr << "duration strftime (ms): " << duration1 << endl;
    cerr << "duration strftime with microseconds (ms): " << duration2 << endl;
    cerr << "duration localtime_r with microseconds (ms): " << duration3 << endl;

    return 0;
}

Results on Ubuntu 16.04 with GCC 5.4.0 and Linux kernel 4.13.0

$ time ./a.out > /dev/null 
duration strftime (ms): 2799
duration strftime with microseconds (ms): 3199
duration localtime_r with microseconds (ms): 1094

real	0m7.098s
user	0m3.521s
sys	0m3.574s

$ time ./a.out | tail
duration strftime (ms): 4421
duration strftime with microseconds (ms): 5041
duration localtime_r with microseconds (ms): 2172
2018-04-10 12:18:23.972529
2018-04-10 12:18:23.972531
2018-04-10 12:18:23.972532
2018-04-10 12:18:23.972534
2018-04-10 12:18:23.972537
2018-04-10 12:18:23.972539
2018-04-10 12:18:23.972540
2018-04-10 12:18:23.972542
2018-04-10 12:18:23.972546
2018-04-10 12:18:23.972547

real	0m11.639s
user	0m5.767s
sys	0m13.516s