Thread: Measuring time

>>All I find...
What you find has absolutely nothing to do with what the standard says.

Here's how one would continue this argument:
- Buy a copy of the standard.
- Read it.
- Assert your interpretations of the standard that support your argument.

Otherwise, read the links provided in this thread and drawn your own conclusions. Here's mine: "If you don't care about portability or adhering to the standard, then do whatever works".

gg

>> Let me quote it:
How bout a real qoute will some section numbers etc.
Then what you'll want to do is explain how the quote supports your argument.

gg

I've done that, you didn't...
Try looking in the time.h section

Well, I usually try to teach folks how to fish, but some just need to be spoon fed…..here's how you quote the standard:

Code:

From: ISO/IEC 9899:1999 (E)

7.23 Date and time <time.h>
7.23.1 Components of time
...
    3 The types declared are size_t (described in 7.17);
      clock_t and time_t which are arithmetic types capable of representing 
      times; and struct tm which holds the components of a calendar time, 
      called the broken-down time.
...
7.23.2.4 The time function
    Synopsis
    1 #include <time.h>
      time_t time(time_t *timer);

    Description
    2 The time function determines the current calendar time. The encoding of 
      the value is unspecified.

    Returns
    3 The time function returns the implementation’s best approximation to 
      the current calendar time. The value (time_t)(-1) is returned if the 
      calendar time is not available. If timer is not a null pointer, the 
      return value is also assigned to the object it points to.

This is from C99 but applies equally to C89.

There's a big difference between arithmetic properties (my original post) and an arithmetic type. The standard defines time_t as arithmetic type so that a comparison to (time_t)(-1) can be made. More importantly, the encoding of the time value is not defined. Meaning it could be seconds, micro-seconds, nano-seconds, or none of the above. The encoding doesn't even have to be in any unit of time, it could be a binary encoded decimal (BCD) of date/time values (adding 20 to a BCD doesn't make any sense).

Under ISO C, time_t is an abstract type for which the only valid arithmetic operation is comparison to (time_t)(-1).

As a side note, under the Single Unix Specification (the current POSIX standard), the time_t value returned by the time() function is defined to be in units of seconds. This is the most common implementation I've seen over the years.

So, (once again) if you're not concerned with portability of source code under ISO C, simply follow the documentation that came with your standard C library implementation. As a contributor to these forums, I'm simply following the convention of pointing out what is standard and what isn't standard (as far as I understand it).

I prefer "boo-yaa" over "busted"

gg