how to solve this linux Timer error - c

Question

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>
#define BILLION 1000000000L;
int main( int argc, char** argv )
{
struct timespec start, stop;
double accum;
uint32 StartTime, StopTime;
if( StartTime = clock_gettime( CLOCK_REALTIME, &start) == -1 ) {
perror( "clock gettime" );
return EXIT_FAILURE;
}
StartTime = start.tv_sec + 0.0000000001 * start.tv_nsec;
system( argv[1] ); // or it could be any calculation
if( StopTime = clock_gettime( CLOCK_REALTIME, &stop) == -1 ) {
perror( "clock gettime" );
return EXIT_FAILURE;
}
StopTime = stop.tv_sec + 0.0000000001 * stop.tv_nsec;
accum = StopTime - StartTime;
printf( "%lf\n", accum );
return EXIT_SUCCESS;
}
This program calculates the time required to
execute the program specified as its first argument.
The time is printed in seconds, on standard out.
I am calculating the start time and stop time to perform some computaion. I am able to get the start time and stop time for the computation but not able to find the difference between the start ans stop time i.e. accum. could anyone help me in this ?

Answer 1

Remove StartTime and StopTime. Declare this function :
double to_double(struct timespec t) {
return t.tv_sec + 0.0000000001 * t.tv_nsec;
}
And you'll get your deltatime this way :
accum = to_double(stop) - to_double(start);

Answer 2

The problem is that StartTime and StopTime are both defined as integer types. The results of your calculations are not whole numbers but because the left hand side of the expressions are integers the results are getting truncated down to the integer part. Essentially, you are loosing the details provided by the tv_nsec field.
As suggested in the comments, declare StartTime and StopTime as doubles to fix that.
Change
uint32 StartTime, StopTime;
to
double StartTime, StopTime;