c - Why is the elapsed time 0? -

i made program unrolls loops , measures time taken sort array, problem have unrolled loop program gives me answer of 0 in nano seconds , can't be. tried monotonic doesn't help. here's code:

    #include <stdio.h>     #include <time.h>     #include <stdlib.h>     #include <sys/types.h>     #include <sys/stat.h>     #include <math.h>     #include <unistd.h>     #define billion  1000000000l     int main()     {         char buf[500];         int numberofelements = 10;         int currenttest = 1;         int randomarray[numberofelements];         int minindex;         int minvalue;         struct timespec requeststart;         struct timespec requestend;         long int recordstarttime;         long int recordendtime;         long int elapsedtime;         file *arrangedarray;         file *stopwatch;         sprintf(buf,"place store file/stopwatch.txt", currenttest);         stopwatch = fopen(buf, "a+");         struct stat st = {0};         sprintf(buf, "the place stored stopwatch file", currenttest);         if (stat(buf, &st) == -1)         {             sprintf(buf, "the place stored stopwatch file", currenttest);             mkdir(buf);         }         sprintf(buf, "the place store program/arrangedarray.txt", currenttest);         arrangedarray = fopen(buf, "w+");         randomarray[0] = 7045;          randomarray[1] = 4949;          randomarray[2] = 24507;          randomarray[3] = 6071;          randomarray[4] = 11820;          randomarray[5] = 11710;          randomarray[6] = 11168;          randomarray[7] = 11234;          randomarray[8] = 11863;          randomarray[9] = 2683;          clock_gettime(clock_process_cputime_id, &requeststart);         recordstarttime = requeststart.tv_nsec + requeststart.tv_sec * billion;         minindex = 0;          minindex = 1;          minindex = 9;          minvalue = randomarray[9];          randomarray[9] = randomarray[0];          randomarray[0] = 2683;          minindex = 1;          minindex = 2;          minindex = 3;          minvalue = randomarray[3];          randomarray[3] = randomarray[2];          randomarray[2] = 6071;          minindex = 3;          minindex = 4;          minindex = 5;          minindex = 6;          minindex = 9;          minvalue = randomarray[9];          randomarray[9] = randomarray[3];          randomarray[3] = 7045;          minindex = 4;          minindex = 5;          minindex = 6;          minvalue = randomarray[6];          randomarray[6] = randomarray[4];          randomarray[4] = 11168;          minindex = 5;          minindex = 7;          minvalue = randomarray[7];          randomarray[7] = randomarray[5];          randomarray[5] = 11234;          minindex = 6;          minindex = 7;          minvalue = randomarray[7];          randomarray[7] = randomarray[6];          randomarray[6] = 11710;          minindex = 7;          minindex = 8;          minindex = 9;          clock_gettime(clock_process_cputime_id, &requestend);         recordendtime = (requestend.tv_nsec + requestend.tv_sec * billion);         elapsedtime = recordendtime - recordstarttime;         sprintf(buf, "%li\n", elapsedtime);         fputs(buf, stopwatch);         sprintf(buf, "%i\n", randomarray[0]);         fputs(buf, arrangedarray);         sprintf(buf, "%i\n", randomarray[1]);         fputs(buf, arrangedarray);         sprintf(buf, "%i\n", randomarray[2]);         fputs(buf, arrangedarray);         sprintf(buf, "%i\n", randomarray[3]);         fputs(buf, arrangedarray);         sprintf(buf, "%i\n", randomarray[4]);         fputs(buf, arrangedarray);         sprintf(buf, "%i\n", randomarray[5]);         fputs(buf, arrangedarray);         sprintf(buf, "%i\n", randomarray[6]);         fputs(buf, arrangedarray);         sprintf(buf, "%i\n", randomarray[7]);         fputs(buf, arrangedarray);         sprintf(buf, "%i\n", randomarray[8]);         fputs(buf, arrangedarray);         sprintf(buf, "%i\n", randomarray[9]);         fputs(buf, arrangedarray);          fclose(arrangedarray);         fclose(stopwatch);         return 0;     }