Portable method of accessing CPU time for given process

Hi, I'm using the following code to print the duration of a program. I'm using clock(), or if available clock_gettime() with CLOCK_PROCESS_CPUTIME_ID.

Code:

#ifdef _POSIX_CPUTIME
#ifdef CLOCK_PROCESS_CPUTIME_ID
#define TELLTIME if( clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &duration1) == 0 ) {\
                            fprintf(stdout, "Time Elapsed: %lf seconds \n",(double)duration1.tv_nsec/NANOSECS);\
                        } else {\
                            perror("Error: clock_gettime() function error: ");\
                        }
#else
#define TELLTIME fprintf(stdout, "Time Elapsed: %.2f seconds.\n", (double)((double)clock()/CLOCKS_PER_SEC));
#endif
#else
#define TELLTIME ;
#endif
...
...
TELLTIME;

I'm just wondering if there's a way of getting the precision of clock_gettime with CLOCK_PROCESS_CPUTIME_ID when the system doesn't define CLOCK_PROCESS_CPUTIME_ID

If anyone has any insight it would be appreciated.

If you do "man clock_gettime", you will see a function called clock_getres, which gives you the "resolution" of the time you get.

It is very unlikely that the function is available if CLOCK_PROCESS_CPUTIME_ID is not defined - as it is part of the documented interface of that function.

Note however that clock() is DEFINED to give CPU-time, it doesn't always do that. For example, in Windows, clock() returns the time elapsed, not the CPU-time used by this process.

--
Mats

Hi matsp, thanks for your comments. I've read through and used clock_getres(), it wasn't defined as was thought. Thanks for the tipoff about clock_getres()! Quite useful.

The application at this point in time is for Linux and other unix-like OSs so I've decided to rely on clock() should CLOCK_PROCESS_CPUTIME_ID not be defined.

Thanks for the comments.

the availability of CLOCK_PROCESS_CPUTIME_ID can be check at compile-time with _POSIX_CPUTIME and _SC_CPUTIME at runtime with sysconf() [man posixoptions; man sysconf]