Calculating Function time in nanoseconds in C code

Question

I need to know how can I calculate the time of a function in C code in nanoseconds. I tried to repeat the function until consume some microseconds. Are there any other funct

Answer 1

Regardless of how you approach this or what type of system/OS you are using, you are getting an approximate answer at best, with considerable variance due to the nature of the problem.

Second, you need a system that supports this kind of call. It's pretty easy if you're using QNX Neutrino:

http://www.qnx.com/developers/docs/6.3.0SP3/neutrino/lib_ref/c/clock_gettime.html

/*
 * This program calculates the time required to
 * execute the program specified as its first argument.
 * The time is printed in seconds, on standard out.
 */
#include 
#include 
#include 
#include 

#define BILLION  1000000000L;

int main( int argc, char** argv )
  {
    struct timespec start, stop;
    double accum;

    if( clock_gettime( CLOCK_REALTIME, &start) == -1 ) {
      perror( "clock gettime" );
      return EXIT_FAILURE;
    }

    system( argv[1] );

    if( clock_gettime( CLOCK_REALTIME, &stop) == -1 ) {
      perror( "clock gettime" );
      return EXIT_FAILURE;
    }

    accum = ( stop.tv_sec - start.tv_sec )
             + (double)( stop.tv_nsec - start.tv_nsec )
               / (double)BILLION;
    printf( "%lf\n", accum );
    return EXIT_SUCCESS;
  }