C에서 밀리초까지 시간차 계산하기

difftime()은 초까지만 계산하기 때문에 밀리초까지 계산해 주는 함수가 필요하다.

/* Written by wje_lq from LinuxQuestions.org */
#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

long long
timeval_diff(struct timeval *difference,
             struct timeval *end_time,
             struct timeval *start_time
            )
{
  struct timeval temp_diff;

  if(difference==NULL)
  {
    difference=&temp_diff;
  }

  difference->tv_sec =end_time->tv_sec -start_time->tv_sec ;
  difference->tv_usec=end_time->tv_usec-start_time->tv_usec;

  /* Using while instead of if below makes the code slightly more robust. */

  while(difference->tv_usec<0)
  {
    difference->tv_usec+=1000000;
    difference->tv_sec -=1;
  }

  return 1000000LL*difference->tv_sec+
                   difference->tv_usec;

} /* timeval_diff() */

int
main(void)
{
  struct timeval earlier;
  struct timeval later;
  struct timeval interval;

  /*
   * There are two ways to call timeval_diff.  The first way simply returns
   * the time difference as microseconds, a single integer.
   */

  if(gettimeofday(&earlier,NULL))
  {
    perror("first gettimeofday()");

    exit(1);
  }

  sleep(3);

  if(gettimeofday(&later,NULL))
  {
    perror("second gettimeofday()");

    exit(1);
  }

  printf("difference is %lld microseconds\n",
         timeval_diff(NULL,&later,&earlier)
        );

  /*
   * The second way to call timeval_diff returns the difference broken down as
   * seconds and microseconds.
   */

  if(gettimeofday(&earlier,NULL))
  {
    perror("third gettimeofday()");

    exit(1);
  }

  sleep(4);

  if(gettimeofday(&later,NULL))
  {
    perror("fourth gettimeofday()");

    exit(1);
  }

  timeval_diff(&interval,&later,&earlier);

  printf("difference is %ld seconds, %ld microseconds\n",
         interval.tv_sec,
         interval.tv_usec
        );

  /*
   * Well, actually there's a third way.  You can actually combine the first
   * two ways.
   */

  if(gettimeofday(&earlier,NULL))
  {
    perror("fifth gettimeofday()");

    exit(1);
  }

  sleep(5);

  if(gettimeofday(&later,NULL))
  {
    perror("sixth gettimeofday()");

    exit(1);
  }

  printf("difference is %lld microseconds",
         timeval_diff(&interval,&later,&earlier)
        );

  printf(" (%ld seconds, %ld microseconds)\n",
         interval.tv_sec,
         interval.tv_usec
        );

  return 0;

} /* main() */

하지만, 윈도의 비주얼 스튜디오에는 sys/time.h 헤더가 없고 gettimeofday() 함수가 정의되어 있지 않다. 그래서 직접 만들어 써야 한다.

time.h

#pragma once

#ifndef _TIMES_H

#include "times.h"

#endif

times.h

#ifndef _TIMES_H
#define _TIMES_H

#ifdef _WIN32
#include <sys/timeb.h>
#include <sys/types.h>
#include <winsock2.h>

int gettimeofday(struct timeval* t,void* timezone);

// from linux's sys/times.h

//#include <features.h>

#define __need_clock_t
#include <time.h>


/* Structure describing CPU time used by a process and its children.  */
struct tms
  {
    clock_t tms_utime;          /* User CPU time.  */
    clock_t tms_stime;          /* System CPU time.  */

    clock_t tms_cutime;         /* User CPU time of dead children.  */
    clock_t tms_cstime;         /* System CPU time of dead children.  */
  };

/* Store the CPU time used by this process and all its
   dead children (and their dead children) in BUFFER.
   Return the elapsed real time, or (clock_t) -1 for errors.
   All times are in CLK_TCKths of a second.  */
clock_t times (struct tms *__buffer);

typedef long long suseconds_t ;

#endif
#endif

time.cpp

#include "times.h"

int gettimeofday(struct timeval* t,void* timezone)
{       struct _timeb timebuffer;
        _ftime( &timebuffer );
        t->tv_sec=timebuffer.time;
        t->tv_usec=1000*timebuffer.millitm;
		return 0;
}

clock_t times (struct tms *__buffer) {

	__buffer->tms_utime = clock();
	__buffer->tms_stime = 0;
	__buffer->tms_cstime = 0;
	__buffer->tms_cutime = 0;
	return __buffer->tms_utime;
}