(g77.info) Year 2000 (Y2K) Problems

(g77.info) Run-time Environment Limits
 
 Year 2000 (Y2K) Problems
 ------------------------
 
    While the `g77' compiler itself is believed to be Year-2000 (Y2K)
 compliant, some intrinsics are not, and, potentially, some underlying
 systems are not, perhaps rendering some Y2K-compliant intrinsics
 non-compliant when used on those particular systems.
 
    Fortran code that uses non-Y2K-compliant intrinsics (listed below)
 is, itself, almost certainly not compliant, and should be modified to
 use Y2K-compliant intrinsics instead.
 
    Fortran code that uses no non-Y2K-compliant intrinsics, but which
 currently is running on a non-Y2K-compliant system, can be made more
 Y2K compliant by compiling and linking it for use on a new
 Y2K-compliant system, such as a new version of an old,
 non-Y2K-compliant, system.
 
    Currently, information on Y2K and related issues is being maintained
 at `http://www.gnu.org/software/year2000-list.html'.
 
    See the following for intrinsics known to have potential problems in
 these areas on at least some systems:  Date Intrinsic, 
 IDate Intrinsic (VXT).
 
    The `libg2c' library shipped with any `g77' that warns about
 invocation of a non-Y2K-compliant intrinsic has renamed the `EXTERNAL'
 procedure names of those intrinsics.  This is done so that the `libg2c'
 implementations of these intrinsics cannot be directly linked to as
 `EXTERNAL' names (which normally would avoid the non-Y2K-intrinsic
 warning).
 
    The renamed forms of the `EXTERNAL' names of these renamed procedures
 may be linked to by appending the string `_y2kbug' to the name of the
 procedure in the source code.  For example:
 
      CHARACTER*20 STR
      INTEGER YY, MM, DD
      EXTERNAL DATE_Y2KBUG, VXTIDATE_Y2KBUG
      CALL DATE_Y2KBUG (STR)
      CALL VXTIDATE_Y2KBUG (MM, DD, YY)
 
    (Note that the `EXTERNAL' statement is not actually required, since
 the modified names are not recognized as intrinsics by the current
 version of `g77'.  But it is shown in this specific case, for purposes
 of illustration.)
 
    The renaming of `EXTERNAL' procedure names of these intrinsics
 causes unresolved references at link time.  For example, `EXTERNAL
 DATE; CALL DATE(STR)' is normally compiled by `g77' as, in C,
 `date_(&str, 20);'.  This, in turn, links to the `date_' procedure in
 the `libE77' portion of `libg2c', which purposely calls a nonexistent
 procedure named `G77_date_y2kbuggy_0'.  The resulting link-time error
 is designed, via this name, to encourage the programmer to look up the
 index entries to this portion of the `g77' documentation.
 
    Generally, we recommend that the `EXTERNAL' method of invoking
 procedures in `libg2c' *not* be used.  When used, some of the
 correctness checking normally performed by `g77' is skipped.
 
    In particular, it is probably better to use the `INTRINSIC' method
 of invoking non-Y2K-compliant procedures, so anyone compiling the code
 can quickly notice the potential Y2K problems (via the warnings
 printing by `g77') without having to even look at the code itself.
 
    If there are problems linking `libg2c' to code compiled by `g77'
 that involve the string `y2kbug', and these are not explained above,
 that probably indicates that a version of `libg2c' older than `g77' is
 being linked to, or that the new library is being linked to code
 compiled by an older version of `g77'.
 
    That's because, as of the version that warns about non-Y2K-compliant
 intrinsic invocation, `g77' references the `libg2c' implementations of
 those intrinsics using new names, containing the string `y2kbug'.
 
    So, linking newly-compiled code (invoking one of the intrinsics in
 question) to an old library might yield an unresolved reference to
 `G77_date_y2kbug_0'.  (The old library calls it `G77_date_0'.)
 
    Similarly, linking previously-compiled code to a new library might
 yield an unresolved reference to `G77_vxtidate_0'.  (The new library
 calls it `G77_vxtidate_y2kbug_0'.)
 
    The proper fix for the above problems is to obtain the latest
 release of `g77' and related products (including `libg2c') and install
 them on all systems, then recompile, relink, and install (as
 appropriate) all existing Fortran programs.
 
    (Normally, this sort of renaming is steadfastly avoided.  In this
 case, however, it seems more important to highlight potential Y2K
 problems than to ease the transition of potentially non-Y2K-compliant
 code to new versions of `g77' and `libg2c'.)
Info Catalog
(g77.info) Timer Wraparounds
(g77.info) Run-time Environment Limits
(g77.info) Array Size
automatically generated byinfo2html