Discrepancy between “time ./main” in terminal vs. <time.h>

Question

After compiling my code in C, I use “time ./main” from the terminal (Mac OS X) and get

real    0m0.004s
user    0m0.001s
sys     0m0.002s

But using <time.h> as described here , I get an elapsed time of 0.000217 seconds. So I'm just wondering how these two measurements differ.

Answer 1

time ./exe will measure more things - loading the exe, starting the program, finishing the program, etc. These are a lot of things, especially of there are loading of dynamic libraries and things like this.

Using time.h you can measure the time from line x to line y - this will not include anything else (like startup time, etc.)

Also note @BasileStarynkevitch 's comment under the question.