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(g77-295.info)Local Equivalence Areas

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Local Equivalence Areas (EQUIVALENCE)
=====================================

   `g77' treats storage-associated areas involving a `COMMON' block as
explained in the section on common blocks.

   A local `EQUIVALENCE' area is a collection of variables and arrays
connected to each other in any way via `EQUIVALENCE', none of which are
listed in a `COMMON' statement.

   Currently, `g77' does not emit "true" debugging information for
members in a local `EQUIVALENCE' area, due to an apparent bug in the
GBE.

   (As of Version 0.5.19, `g77' does emit debugging information for such
members in the form of a constant string specifying the base name of
the aggregate area and the offset of the member in bytes from the start
of the area.  Use the `-fdebug-kludge' option to enable this behavior.
In `gdb', use `set language c' before printing the value of the member,
then `set language fortran' to restore the default language, since
`gdb' doesn't provide a way to print a readable version of a character
string in Fortran language mode.

   This kludge will be removed in a future version of `g77' that, in
conjunction with a contemporary version of `gdb', properly supports
Fortran-language debugging, including access to members of
`EQUIVALENCE' areas.)

   Note: Options for Code Generation Conventions, for
information on the `-fdebug-kludge' option.

   Moreover, `g77' implements a local `EQUIVALENCE' area such that its
type is an array of the C `char' data type.

   The name `g77' gives this array of `char' type is `__g77_equiv_X',
where X is the name of the item that is placed at the beginning (offset
0) of this array.  If more than one such item is placed at the
beginning, X is the name that sorts to the top in an alphabetical sort
of the list of such items.

   When debugging, you must therefore access members of `EQUIVALENCE'
areas by specifying the appropriate `__g77_equiv_X' array section with
the appropriate offset.  See the explanation of debugging `COMMON'
blocks for info applicable to debugging local `EQUIVALENCE' areas.

   (*Note:* `g77' version 0.5.18 and earlier chose the name for X using
a different method when more than one name was in the list of names of
entities placed at the beginning of the array.  Though the
documentation specified that the first name listed in the `EQUIVALENCE'
statements was chosen for X, `g77' in fact chose the name using a
method that was so complicated, it seemed easier to change it to an
alphabetical sort than to describe the previous method in the
documentation.)