Re: Windows file timestamp converted to local time

Re: Windows file timestamp converted to local time

[Matt Borchers]

Below is the function from System.OS_Lib. 
Does anybody know where the C implementation can be found?
Does anybody know where the C implementation of "localtime" is found?

   function File_Time_Stamp (Name : C_File_Name) return OS_Time is
      function File_Time (Name : Address) return OS_Time;
      pragma Import (C, File_Time, "__gnat_file_time_name");
   begin
      return File_Time (Name);
   end File_Time_Stamp;

Re: Windows file timestamp converted to local time

[Niklas Holsti]

On 2023-10-16 21:35, Matt Borchers wrote:
> Below is the function from System.OS_Lib.
> Does anybody know where the C implementation can be found?
> Does anybody know where the C implementation of "localtime" is found?
> 
>     function File_Time_Stamp (Name : C_File_Name) return OS_Time is
>        function File_Time (Name : Address) return OS_Time;
>        pragma Import (C, File_Time, "__gnat_file_time_name");
>     begin
>        return File_Time (Name);
>     end File_Time_Stamp;


(This question seems to be a follow-up ("Re:") to some earlier post, but 
my newsreader does not seem to find or show that earlier post.)

What is the problem?

Have you tried using the standard Ada services: 
Ada.Directories.Modification_Time and 
Ada.Calendar.Time_Zones.Local_Time_Offset?

Re: Windows file timestamp converted to local time

[Randy Brukardt]

"Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message 
news:kp5eucFogqpU1@mid.individual.net...
> On 2023-10-16 21:35, Matt Borchers wrote:
>> Below is the function from System.OS_Lib.
>> Does anybody know where the C implementation can be found?
>> Does anybody know where the C implementation of "localtime" is found?
>>
>>     function File_Time_Stamp (Name : C_File_Name) return OS_Time is
>>        function File_Time (Name : Address) return OS_Time;
>>        pragma Import (C, File_Time, "__gnat_file_time_name");
>>     begin
>>        return File_Time (Name);
>>     end File_Time_Stamp;
>
>
> (This question seems to be a follow-up ("Re:") to some earlier post, but 
> my newsreader does not seem to find or show that earlier post.)
>
> What is the problem?
>
> Have you tried using the standard Ada services: 
> Ada.Directories.Modification_Time and 
> Ada.Calendar.Time_Zones.Local_Time_Offset?

...as those will work on (almost) any target system, while the actual 
implementation is going to be rather OS-dependent. And there never is a good 
reason to use a GNAT-only (or any compiler-specific, for any compiler) 
facility when there is an equivalent standard facility. Most of those 
facilities pre-date the Ada ones.

                Randy.

Re: Windows file timestamp converted to local time

[Matt Borchers]

On Monday, October 16, 2023 at 2:49:52 PM UTC-4, Niklas Holsti wrote:
> On 2023-10-16 21:35, Matt Borchers wrote: 
> > Below is the function from System.OS_Lib. 
> > Does anybody know where the C implementation can be found? 
> > Does anybody know where the C implementation of "localtime" is found? 
> > 
> > function File_Time_Stamp (Name : C_File_Name) return OS_Time is 
> > function File_Time (Name : Address) return OS_Time; 
> > pragma Import (C, File_Time, "__gnat_file_time_name"); 
> > begin 
> > return File_Time (Name); 
> > end File_Time_Stamp;
> (This question seems to be a follow-up ("Re:") to some earlier post, but 
> my newsreader does not seem to find or show that earlier post.) 
> 
> What is the problem? 
> 
> Have you tried using the standard Ada services: 
> Ada.Directories.Modification_Time and 
> Ada.Calendar.Time_Zones.Local_Time_Offset?

Thank you for the suggestion of using "Ada.Directories.Modification_Time". I didn't think to look in that package. This function adjusts for daylight savings time and returns the time as displayed in Windows Explorer.

There needs to be better comments (and documentation) for these time related functions. It is often not clear what time is returned. It is safe to assume UTC or local time, but the daylight savings issue caused confusion.

Re: Windows file timestamp converted to local time

[Niklas Holsti]

On 2023-10-17 17:13, Matt Borchers wrote:
> On Monday, October 16, 2023 at 2:49:52 PM UTC-4, Niklas Holsti wrote:
>> On 2023-10-16 21:35, Matt Borchers wrote:
>>> Below is the function from System.OS_Lib.
>>> Does anybody know where the C implementation can be found?
>>> Does anybody know where the C implementation of "localtime" is found?
>>>
>>> function File_Time_Stamp (Name : C_File_Name) return OS_Time is
>>> function File_Time (Name : Address) return OS_Time;
>>> pragma Import (C, File_Time, "__gnat_file_time_name");
>>> begin
>>> return File_Time (Name);
>>> end File_Time_Stamp;
>> (This question seems to be a follow-up ("Re:") to some earlier post, but
>> my newsreader does not seem to find or show that earlier post.)
>>
>> What is the problem?
>>
>> Have you tried using the standard Ada services:
>> Ada.Directories.Modification_Time and
>> Ada.Calendar.Time_Zones.Local_Time_Offset?
> 
> Thank you for the suggestion of using "Ada.Directories.Modification_Time".


Happy to help!


> I didn't think to look in that package.


Ada.Directories does, IMO, seem the best place for it, since it should 
not depend on the type of the file -- text, sequential, etc.


> This function adjusts for daylight savings time and returns the time
> as displayed in Windows Explorer.
> 
> There needs to be better comments (and documentation) for these time
> related functions. It is often not clear what time is returned.


Yes, but some of that documentation should not be in the Ada standard, 
but in the compiler's documentation.

Ada.Directories.Modification_Time returns a value of type 
Ada.Calendar.Time. However, "the time base associated with the type Time 
of package Calendar is implementation defined" (RM 9.6(23)) so it should 
be documented in the implementation documents, that is in the GNAT 
documentation. Have you looked there?

Re: Windows file timestamp converted to local time

[Simon Wright]

Niklas Holsti <niklas.holsti@tidorum.invalid> writes:

> Ada.Directories.Modification_Time returns a value of type
> Ada.Calendar.Time. However, "the time base associated with the type
> Time of package Calendar is implementation defined" (RM 9.6(23)) so it
> should be documented in the implementation documents, that is in the
> GNAT documentation. Have you looked there?

The GNAT RM says in Implementation Defined Characteristics[1]

"The time base used is that provided by the C library function gettimeofday."

[1] https://docs.adacore.com/live/wave/gnat_rm/html/gnat_rm/gnat_rm/implementation_defined_characteristics.html

Re: Windows file timestamp converted to local time

[Simon Wright]

Matt Borchers <mattborchers@gmail.com> writes:

> Below is the function from System.OS_Lib. 
> Does anybody know where the C implementation can be found?
> Does anybody know where the C implementation of "localtime" is found?
>
>    function File_Time_Stamp (Name : C_File_Name) return OS_Time is
>       function File_Time (Name : Address) return OS_Time;
>       pragma Import (C, File_Time, "__gnat_file_time_name");
>    begin
>       return File_Time (Name);
>    end File_Time_Stamp;

For the first question, very likely to be in gcc/ada/adaint.c in the GCC
sources (https://github.com/gcc-mirror/gcc)

localtime() is in libc; depends on your OS.

Re: Windows file timestamp converted to local time

[Dmitry A. Kazakov]

On 2023-10-16 20:35, Matt Borchers wrote:
> Below is the function from System.OS_Lib.
> Does anybody know where the C implementation can be found?
> Does anybody know where the C implementation of "localtime" is found?
> 
>     function File_Time_Stamp (Name : C_File_Name) return OS_Time is
>        function File_Time (Name : Address) return OS_Time;
>        pragma Import (C, File_Time, "__gnat_file_time_name");
>     begin
>        return File_Time (Name);
>     end File_Time_Stamp;

If I correctly interpret the description, OS_Time is FILETIME under 
Windows, i.e. 64-bit value.

https://learn.microsoft.com/en-us/windows/win32/api/minwinbase/ns-minwinbase-filetime

As for implementation it likely calls to GetFileTime after obtaining a 
handle to the file.

https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getfiletime

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de