How to use clock in C

Question

How do I call clock   in C     For example  I want to test how much time a linear search takes to find a given element in an array

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include  lt iostream gt   include  lt cstdio gt   include  lt ctime gt   int main         std  clock t start      double duration       start   std  clock            Your algorithm here         duration     std  clock   - start      double  CLOCKS PER SEC       std  cout lt  lt  printf    lt  lt  duration  lt  lt   n

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you can measure how long your program works  The following functions help measure the CPU time since the start of the program    C    double clock     CLOCKS PER SEC with ctime included  python time clock   returns floating-point value in seconds  Java System nanoTime   returns long value in nanoseconds    my reference  Algorithms toolbox week 1 course part of data structures and algorithms specialization by University of California San Diego  amp  National Research University Higher School of Economics  so you can add this line of code after your algorithm  cout  lt  lt   double clock     CLOCKS PER SEC     Expected Output  the output representing the number of clock ticks per second

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Probably you might be interested in timer like this   H   M   S   Msec   the code in Linux OS    include  lt iostream gt   include  lt unistd h gt   using namespace std  void newline      int main      int msec   0  int sec   0  int min   0  int hr   0      cout  lt  lt   Press any key to start      char start    gtech     for                newline                    if msec    1000                                              sec                          msec   0                                    if sec    60                                              min                          sec   0                                     if min    60                                              hr                          min   0                            cout  lt  lt  hr  lt  lt         lt  lt  min  lt  lt         lt  lt  sec  lt  lt         lt  lt  msec  lt  lt  endl            msec          usleep 100000            return 0     void newline             cout  lt  lt    n n n n n n n n n n n n n n n n n n n n n n n n n n n n n n n

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clock   returns the number of clock ticks since your program started  There is a related constant  CLOCKS PER SEC  which tells you how many clock ticks occur in one second  Thus  you can test any operation like this   clock t startTime   clock    doSomeOperation    clock t endTime   clock    clock t clockTicksTaken   endTime - startTime  double timeInSeconds   clockTicksTaken    double  CLOCKS PER SEC

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An alternative solution  which is portable and with higher precision  available since C  11  is to use std  chrono   Here is an example    include  lt iostream gt   include  lt chrono gt  typedef std  chrono  high resolution clock Clock   int main         auto t1   Clock  now        auto t2   Clock  now        std  cout  lt  lt   Delta t2-t1                    lt  lt  std  chrono  duration cast lt std  chrono  nanoseconds gt  t2 - t1  count                  lt  lt    nanoseconds   lt  lt  std  endl      Running this on ideone com gave me   Delta t2-t1  282 nanoseconds

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On Windows at least  the only practically accurate measurement mechanism is QueryPerformanceCounter  QPC   std  chrono is implemented using it  since VS2015  if you use that   but it is not accurate to the same degree as using QueryPerformanceCounter directly  In particular it s claim to report at 1 nanosecond granularity is absolutely not correct  So  if you re measuring something that takes a very short amount of time  and your case might just be such a case   then you should use QPC  or the equivalent for your OS  I came up against this when measuring cache latencies  and I jotted down some notes that you might find useful  here   https   github com jarlostensen notesandcomments blob master stdchronovsqcp md

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include  lt iostream gt   include  lt ctime gt   include  lt cstdlib gt     sleep    --- just a function that waits a certain amount of milliseconds  using namespace std   int main          clock t cl        initializing a clock type      cl   clock        starting time of clock       sleep 5167       insert code here      cl   clock   - cl     end point of clock       sleep 1000       testing to see if it actually stops at the end point      cout  lt  lt  cl  double CLOCKS PER SEC  lt  lt  endl     prints the determined ticks per second  seconds passed        return 0       outputs  5 17

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