How do I measure a time interval in C

Question

I would like to measure time in C  and I am having a tough time figuring it out  all I want is something like this    start a timer run a method stop the timer report the time taken  at least to micro accuracy    Any help would be appreciated    I am compiling in windows using mingw

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If your Linux system supports it  clock gettime CLOCK MONOTONIC  should be a high resolution timer that is unaffected by system date changes  e g  NTP daemons

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Using the time h library  try something like this   long start time  end time  elapsed   start time   clock       Do something end time   clock     elapsed    end time - start time    CLOCKS PER SEC   1000

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Great answers for GNU environments above and below      But    what if you re not running on an OS   or a PC for that matter  or you need to time your timer interrupts themselves   Here s a solution that uses the x86 CPU timestamp counter directly    Not because this is good practice  or should be done  ever  when running under an OS       Caveat  Only works on x86  with frequency scaling disabled   Under Linux  only works on non-tickless kernels   rdtsc c    include  lt sys time h gt   include  lt time h gt   include  lt stdio h gt   include  lt stdlib h gt   include  lt string h gt   typedef unsigned long long int64   static   inline   int64 getticks void         unsigned a  d       asm volatile  rdtsc      a   a     d   d         return    int64 a       int64 d   lt  lt  32       int main          int64 tick tick1       unsigned time 0 mt           mt is the divisor to give microseconds       FILE  pf       int i r l n 0       char s 100            time how long it takes to get the divisors  as a test       tick   getticks             get the divisors  - todo  for max performance this can          output a new binary or library with these values hardcoded          for the relevant CPU - if you use the equivalent assembler for         that CPU      pf   fopen   proc cpuinfo   r         do         r fscanf pf   s   amp s 0          if  r lt 0           n 5  break          else if  n  0           if  strcmp  MHz  s   0  n 1          else if  n  1           if  strcmp     s   0  n 2          else if  n  2           n 3                  while  n lt 3        fclose pf         s 9   char 0       strcpy  amp s 4   amp s 5         mt atoi s         printf   define mt  u      s Hz  hardcode this for your a CPU-specific binary  -  n  mt s         tick1   getticks         time    unsigned   tick1-tick  mt        printf   u ms n  time            time the duration of sleep 1  - plus overheads  -       tick   getticks          sleep 1         tick1   getticks         time    unsigned   tick1-tick  mt        printf   u ms n  time         return 0      compile and run with       gcc rdtsc c -o rdtsc  amp  amp    rdtsc   It reads the divisor for your CPU from  proc cpuinfo and shows how long it took to read that in microseconds  as well as how long it takes to execute sleep 1  in microseconds    Assuming the Mhz rating in  proc cpuinfo always contains 3 decimal places  -o

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The following is a group of versatile C functions for timer management based on the gettimeofday   system call  All the timer properties are contained in a single ticktimer struct - the interval you want  the total running time since the timer initialization  a pointer to the desired callback you want to call  the number of times the callback was called  A callback function would look like this   void your timer cb  struct ticktimer  t         do your stuff here        To initialize and start a timer  call ticktimer init your timer  interval  TICKTIMER RUN  your timer cb  0    In the main loop of your program call ticktimer tick your timer  and it will decide whether the appropriate amount of time has passed to invoke the callback   To stop a timer  just call ticktimer ctl your timer  TICKTIMER STOP    ticktimer h    ifndef   TICKTIMER H  define   TICKTIMER H   include  lt stdio h gt   include  lt stdlib h gt   include  lt unistd h gt   include  lt sys time h gt   include  lt sys types h gt    define TICKTIMER STOP         0x00  define TICKTIMER UNCOMPENSATE 0x00  define TICKTIMER RUN          0x01  define TICKTIMER COMPENSATE   0x02  struct ticktimer     u int64 t tm tick interval    u int64 t tm last ticked    u int64 t tm total    unsigned ticks total    void   tick  struct ticktimer       unsigned char flags    int id      void ticktimer init  struct ticktimer    u int64 t  unsigned char  void     struct ticktimer     int   unsigned ticktimer tick  struct ticktimer     void ticktimer ctl  struct ticktimer    unsigned char   struct ticktimer  ticktimer alloc  void   void ticktimer free  struct ticktimer     void ticktimer tick all  void     endif   ticktimer c    include  ticktimer h    define TIMER COUNT 100  static struct ticktimer timers TIMER COUNT   static struct timeval tm          brief     Initializes sets the ticktimer struct      param timer     Pointer to ticktimer struct     param interval     Ticking interval in microseconds     param flags     Flag bitmask  Use TICKTIMER RUN   TICKTIMER COMPENSATE     to start a compensating timer  TICKTIMER RUN to start     a normal uncompensating timer     param tick     Ticking callback function     param id     Timer ID  Useful if you want to distinguish different     timers within the same callback function     void ticktimer init  struct ticktimer  timer  u int64 t interval  unsigned char flags  void   tick  struct ticktimer     int id      gettimeofday  amp tm  NULL     timer- gt tm tick interval   interval    timer- gt tm last ticked   tm tv sec   1000000   tm tv usec    timer- gt tm total   0    timer- gt ticks total   0    timer- gt tick   tick    timer- gt flags   flags    timer- gt id   id            brief      Checks the status of a ticktimer and performs a tick s  if      necessary      param timer     Pointer to ticktimer struct      return     The number of times the timer was ticked     unsigned ticktimer tick  struct ticktimer  timer      register typeof timer- gt tm tick interval  now    register typeof timer- gt ticks total  nticks  i     if  timer- gt flags  amp  TICKTIMER RUN        gettimeofday  amp tm  NULL       now   tm tv sec   1000000   tm tv usec       if  now  gt   timer- gt tm last ticked   timer- gt tm tick interval          timer- gt tm total    now - timer- gt tm last ticked         if  timer- gt flags  amp  TICKTIMER COMPENSATE            nticks    now - timer- gt tm last ticked    timer- gt tm tick interval          timer- gt tm last ticked   now -   now - timer- gt tm last ticked    timer- gt tm tick interval            for  i   0  i  lt  nticks  i                timer- gt tick timer             timer- gt ticks total               if  timer- gt tick    NULL                break                                 return nticks          else           timer- gt tm last ticked   now          timer- gt tick timer           timer- gt ticks total            return 1                       return 0            brief     Controls the behaviour of a ticktimer      param timer     Pointer to ticktimer struct     param flags     Flag bitmask     inline void ticktimer ctl  struct ticktimer  timer  unsigned char flags      timer- gt flags   flags            brief     Allocates a ticktimer struct from an internal     statically allocated list      return     Pointer to the newly allocated ticktimer struct     or NULL when no more space is available     struct ticktimer  ticktimer alloc  void      register int i     for  i   0  i  lt  TIMER COUNT  i          if  timers i  tick    NULL          return timers   i               return NULL            brief     Marks a previously allocated ticktimer struct as free      param timer     Pointer to ticktimer struct  usually returned by      ticktimer alloc       inline void ticktimer free  struct ticktimer  timer      timer- gt tick   NULL            brief     Checks the status of all allocated timers from the      internal list and performs ticks where necessary      note     Should be called in the main loop     inline void ticktimer tick all  void      register int i     for  i   0  i  lt  TIMER COUNT  i          if  timers i  tick    NULL          ticktimer tick timers   i

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High resolution timers that provide a resolution of 1 microsecond are system-specific  so you will have to use different methods to achieve this on different OS platforms  You may be interested in checking out the following article  which implements a cross-platform C   timer class based on the functions described below    Song Ho Ahn - High Resolution Timer  1    Windows The Windows API provides extremely high resolution timer functions  QueryPerformanceCounter    which returns the current elapsed ticks  and QueryPerformanceFrequency    which returns the number of ticks per second  Example   include  lt stdio h gt   include  lt windows h gt                    for Windows APIs  int main void        LARGE INTEGER frequency            ticks per second     LARGE INTEGER t1  t2               ticks     double elapsedTime          get ticks per second     QueryPerformanceFrequency  amp frequency           start timer     QueryPerformanceCounter  amp t1           do something                    stop timer     QueryPerformanceCounter  amp t2           compute and print the elapsed time in millisec     elapsedTime    t2 QuadPart - t1 QuadPart    1000 0   frequency QuadPart      printf  quot  f ms  n quot   elapsedTime      Linux  Unix  and Mac For Unix or Linux based system  you can use gettimeofday    This function is declared in  quot sys time h quot   Example   include  lt stdio h gt   include  lt sys time h gt                    for gettimeofday    int main void        struct timeval t1  t2      double elapsedTime          start timer     gettimeofday  amp t1  NULL           do something                    stop timer     gettimeofday  amp t2  NULL           compute and print the elapsed time in millisec     elapsedTime    t2 tv sec - t1 tv sec    1000 0          sec to ms     elapsedTime     t2 tv usec - t1 tv usec    1000 0       us to ms     printf  quot  f ms  n quot   elapsedTime

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On Linux you can use clock gettime     clock gettime CLOCK PROCESS CPUTIME ID   amp start      get initial time-stamp         do stuff         clock gettime CLOCK PROCESS CPUTIME ID   amp end        get final time-stamp  double t ns    double  end tv sec - start tv sec    1 0e9                  double  end tv nsec - start tv nsec                                                       subtract time-stamps and                                                     multiply to get elapsed                                                     time in ns

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Here s a header file I wrote to do some simple performance profiling  using manual timers     ifndef   ZENTIMER H    define   ZENTIMER H     ifdef ENABLE ZENTIMER   include  lt stdio h gt   ifdef WIN32  include  lt windows h gt   else  include  lt sys time h gt   endif  ifdef HAVE STDINT H  include  lt stdint h gt   elif HAVE INTTYPES H  include  lt inttypes h gt   else typedef unsigned char uint8 t  typedef unsigned long int uint32 t  typedef unsigned long long uint64 t   endif   ifdef   cplusplus extern  C     pragma    endif      cplusplus      define ZTIME USEC PER SEC 1000000     ztime t represents usec    typedef uint64 t ztime t    ifdef WIN32 static uint64 t ztimer freq   0   endif  static void ztime  ztime t  ztimep     ifdef WIN32     QueryPerformanceCounter   LARGE INTEGER    ztimep    else     struct timeval tv       gettimeofday   amp tv  NULL         ztimep     uint64 t  tv tv sec   ZTIME USEC PER SEC    tv tv usec   endif    enum       ZTIMER INACTIVE   0      ZTIMER ACTIVE      1  lt  lt  0       ZTIMER PAUSED      1  lt  lt  1       typedef struct       ztime t start      ztime t stop      int state    ztimer t    define ZTIMER INITIALIZER   0  0  0       default timer    static ztimer t   ztimer   ZTIMER INITIALIZER   static void ZenTimerStart  ztimer t  ztimer        ztimer   ztimer   ztimer    amp   ztimer       ztimer- gt state   ZTIMER ACTIVE      ztime   amp ztimer- gt start      static void ZenTimerStop  ztimer t  ztimer        ztimer   ztimer   ztimer    amp   ztimer       ztime   amp ztimer- gt stop       ztimer- gt state   ZTIMER INACTIVE     static void ZenTimerPause  ztimer t  ztimer        ztimer   ztimer   ztimer    amp   ztimer       ztime   amp ztimer- gt stop       ztimer- gt state    ZTIMER PAUSED     static void ZenTimerResume  ztimer t  ztimer        ztime t now  delta       ztimer   ztimer   ztimer    amp   ztimer          unpause        ztimer- gt state  amp    ZTIMER PAUSED       ztime   amp now           calculate time since paused        delta   now - ztimer- gt stop          adjust start time to account for time elapsed since paused        ztimer- gt start    delta     static double ZenTimerElapsed  ztimer t  ztimer  uint64 t  usec     ifdef WIN32     static uint64 t freq   0      ztime t delta  stop       if  freq    0          QueryPerformanceFrequency   LARGE INTEGER     amp freq    else  define freq ZTIME USEC PER SEC     ztime t delta  stop   endif      ztimer   ztimer   ztimer    amp   ztimer       if  ztimer- gt state    ZTIMER ACTIVE          stop   ztimer- gt stop      else         ztime   amp stop        delta   stop - ztimer- gt start       if  usec    NULL           usec    uint64 t   delta     double  ZTIME USEC PER SEC    double  freq         return  double  delta    double  freq     static void ZenTimerReport  ztimer t  ztimer  const char  oper        fprintf  stderr   ZenTimer   s took   6f seconds n   oper  ZenTimerElapsed  ztimer  NULL        ifdef   cplusplus    endif      cplusplus      else      ENABLE ZENTIMER      define ZenTimerStart ztimerp   define ZenTimerStop ztimerp   define ZenTimerPause ztimerp   define ZenTimerResume ztimerp   define ZenTimerElapsed ztimerp  usec   define ZenTimerReport ztimerp  oper    endif    ENABLE ZENTIMER      endif      ZENTIMER H        The ztime   function is the main logic you need     it gets the current time and stores it in a 64bit uint measured in microseconds  You can then later do simple math to find out the elapsed time   The ZenTimer    functions are just helper functions to take a pointer to a simple timer  struct  ztimer t  which records the start time and the end time  The ZenTimerPause   ZenTimerResume   functions allow you to  well  pause and resume the timer in case you want to print out some debugging information that you don t want timed  for example   You can find a copy of the original header file at http   www gnome org  fejj code zentimer h in the off chance that I messed up the html escaping of  lt  s or something  It s licensed under MIT X11 so feel free to copy it into any project you do

[c] How do I measure a time interval in C?

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