Question

So this is pretty basic, but I don’t really know C.

I want to find the number of milliseconds something takes to run, not clock (CPU) cycles.

I tried using

struct timeval start,end;
double dif;

gettimeofday(&start, 0);
//do stuff
gettimeofday(&end, 0);
dif = (end - start) / 1000.0;
printf("The time taken was %lf \n",dif);

I’m getting this error when I’m trying to compile:

bubble.c: In function ‘main’:
bubble.c:55: error: invalid
operands to binary – (have ‘struct timeval’ and ‘struct timeval’)

Answer 1

Change

dif = (end - start) * 1000;

to

dif = (end.tv_sec - start.tv_sec) * 1000 
+ (end.tv_usec - start.tv_usec) / 1000;

In pseudocode:

Get the seconds part of the time delta
Multiply by 1000 to get milliseconds
Get the microseconds part of the time delta
Divide that part by 1000
Add that part to the milliseconds from seconds delta