Re: How to convert Oracle Database Date Type to C time_t

Michel Cadot wrote:
>
> Ellen,
>
> I think you're wrong with operations on date type.
> Your select can be (t as long):
> select
> to_number( to_char(datecol,'J'))*24*60*60+to_number(to_char(datecol,'SSSSS')) -
> (to_number(to_char(to_date('01/01/1970','DD/MM/YYYY'),'J'))*24*60*60
> +to_number(to_char(to_date('01/01/1970','DD/MM/YYYY'),'SSSSS')) )
> into :t
> from ...;
>
> This gives you the number of seconds since 01/01/1970.
> Has time_t type a particuliar structure?

No. The encoding you describe is common, but it is not required by the C Standard, which requires only that a time_t be an arithmetic type capable of representing times. For example it could be a long double representing the number of days since the birth of Brian Kernighan (one of the co-inventors of C).

As a result there's no way that Oracle could reliably map a date type to a time_t for all environments.

The simplest and most portable way to do the translation is: let Oracle format the date and time into the various components of a struct tm and then call mktime().

Scott McKellar mck9_at_swbell.net
Free PL/SQL utilities at http:://home.swbell.net/mck9/pls/

> ellen111_at_my-deja.com a écrit dans le message <7pgnl5$kgj$1_at_nnrp1.deja.com>...
> >Hi, when I try to retrieve date from oracle database, and convert it
> >to time_t type, I have some questions.
> >
> >the way now I used is:
> >select date into char from oracle database, then convert char
> >to time_t(I wrote a function by myself). and it is not very efficient.
> >
> >I was told that there is a way to convert them directly:
> >select date into time_t(? or long, because there is no time_t date
> >type in pro*C), following is my code:
> >
> >EXEC SQL BEGIN DECLARE SECTION;
> >time_t t; //this got an error when precompile
> >long t; //?
> >EXEC SQL END DECLARE SECTION;
> >....
> >EXEC SQL SELECT ((new_time(date,'EST','GMT') -
> > to_date('01-jan-1970','dd-mon-yyyy'))*24*60*60)
> > INTO :t
> > FROM .....
> >printf("time=%d\n",t);
> >
> >but it returns 0 to me...
> >any advises please!
Received on Thu Aug 19 1999 - 20:05:44 CDT