Thanks Rasmus,
Would it also be possible to remove the strftime comment:
John Baxendale
15-Oct-2003 05:15
"Note that on Linux kernels before 2.4.* the date functions in PHP will
happily accept a date before 01-01-1970 as stated at the top of this man
page, post kernel 2.4.* the date functions *do not* work with dates before
1970."
As you say, this is a libc problem, not a kernel problem.
Thanks,
Ross
> Yes, the note on the strftime() page doesn't match the code, you are
> right. We will fix that. What determines whether an OS supports
> negative timestamps or not is the libc implementation. Most UNIX
> operating systems support it and Windows doesn't. In fact some
> functions on Windows will crash if you pass them a negative timestamp.
>
> We'll fix strftime() to allow negative timestamps on non-Windows to
> match the documentation and work on getting a note added to each page
> that takes a timestamp that warns the user that this is a
> platform-dependant feature.
>
> -Rasmus
>
> On Tue, 30 Mar 2004, Ross P. Davis wrote:
>
>> Good day,
>>
>> I would like to bring up a few issues regarding negative timestamps.
>> Firstly, I think it would be good to compose a document that discusses
>> UNIX timestamps and the support or lack thereof regarding negative
>> timestamps on various systems. For example, what is it about a system
>> that gives it negative timestamp support as opposed to not? This
>> document needs to be very clear because there is a lot of FUD floating
>> around on the web about this. Once such a document has been composed,
>> every PHP date function should have the following note:
>>
>> "WARNING: the range of dates that the PHP date functions can handle
>> are dependent on your system's implementation of UNIX timestamps.
>> Please click here [link to timestamp document] for more information."
>>
>> You can then remove all the little notes that are scattered through
>> the function docs regarding windows timestamp support and pre-1970 and
>> so on.
>>
>> Now I would like to discuss the documentation for strftime. In the
>> docs, I see this:
>>
>> "Additionally, not all platforms support negative timestamps,
>> therefore your date range may be limited to no earlier than the Unix
>> epoch. This means that e.g. %e, %T, %R and %D (there might be more)
>> and dates prior to Jan 1, 1970 will not work on Windows, some Linux
>> distributions, and a few other operating systems."
>>
>> This statement is somewhat misleading because as far as I can tell,
>> negative timestamps are not supported AT ALL for strftime. Looking
>> inside the function definition for strftime in
>> php-4.3.5/ext/standard/datetime.c, I see this code following the
>> extraction of the function arguments:
>>
>> 843 if (timestamp < 0) {
>> 844 RETURN_FALSE;
>> 845 }
>>
>> Unless I am missing something, this means that strftime always returns
>> false when working with negative timestamps. As a brief aside, I
>> commented out line 844, recompiled, and tried calling strftime with a
>> negative timestamp - it returned the correct result. I am assuming
>> there is a reason to disallow negative timestamps in this function,
>> but there are no comments in the code to suggest why. As another
>> documentation item, it would be nice to have something like:
>>
>> 843 // disallow negative timestamp b/c [INSERT REASON
>> HERE]
>> 844 if (timestamp < 0) {
>> 845 RETURN_FALSE;
>> 846 }
>>
>> Back to the strftime docs, I see a user comment:
>>
>> "Note that on Linux kernels before 2.4.* the date functions in PHP
>> will happily accept a date before 01-01-1970 as stated at the top of
>> this man page, post kernel 2.4.* the date functions *do not* work with
>> dates before 1970.
>>
>> If you've existing scripts doing date validation on dates before 1970,
>> check them before you upgrade your kernel!"
>>
>> Is this for real? And looking on a site that offers a date function
>> package: http://php.weblogs.com/adodb_date_time_library I see this:
>> "Since RedHat 7.3, negative timestamps are not supported in glibc. So
>> the latest versions of this library will take over negative timestamp
>> calculations on all platforms."
>>
>> So where does the problem lie? Is it in the kernel, glibc, or both?
>> Another thing that needs to be documented is which functions support
>> negative timestamps and which do not. strftime obviously does not.
>> This appears to work on my Redhat 8 system:
>>
>> date("d/m/Y", -1735281789)
>>
>> and yet the following returns -1:
>>
>> strtotime("-50 years");
>>
>> Though it works on older versions of Redhat. So if my system does not
>> support negative timestamps, why does date() operate correctly with a
>> negative timestamp? And why can I correctly run a C program that uses
>> a negative timestamp:
>>
>> #include <time.h>
>> #include <stdio.h>
>>
>> main() {
>> time_t t = -1735281789;
>> printf("%s\n",ctime(&t));
>> char s[80];
>> const struct tm *nowstruct;
>> nowstruct = localtime(&t);
>> strftime(s, 80, "%m/%d/%Y", nowstruct);
>> printf("%s\n",s);
>> }
>>
>> Produces output:
>>
>> Tue Jan 5 12:16:51 1915
>>
>> 01/05/1915
>>
>> My sysadmins want to upgrade the production servers, but we have a
>> massive amount of legacy PHP code that uses the date functions all
>> over the place. Without more in-depth documentation of the PHP
>> functions with regards to these timestamp issues, I cannot know what
>> code is safe to leave alone and what code must be changed. Due to the
>> nature of this code, the less I touch it, the better.
>>
>> I would happy to contribute in any way possible with regards to this
>> matter.
>>
>> Thanks,
>> Ross
>>
