[Bug fortran/47605] New: Document that C_Bool might be the wrong constant for C Booleans

[Bug fortran/47605] New: Document that C_Bool might be the wrong constant for C Booleans

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47605

           Summary: Document that C_Bool might be the wrong constant for C
                    Booleans
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Keywords: documentation
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: burnus@gcc.gnu.org


James pointed out the following at
http://groups.google.com/group/comp.lang.fortran/browse_thread/thread/3c2784c55d402ced

c_bool is typically one byte wide, and c_int 4. That means: Most C programs -
except of those few which explicitly use _Bool, use a 4 byte and not a 1 byte
Boolean variables.

I think one should put a warning into the manual - either in the C Binding part
[1] or in the section about the ISO C Binding constants [2], or in both.

[1] http://gcc.gnu.org/onlinedocs/gfortran/Intrinsic-Types.html
[2]http://gcc.gnu.org/onlinedocs/gfortran/ISO_005fC_005fBINDING.html

[Bug fortran/47605] Document that C_Bool might be the wrong constant for C Booleans

[dominiq at lps dot ens.fr]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47605

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2014-03-22
     Ever confirmed|0                           |1

--- Comment #1 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
In [1] I see

> For logical types, please note that the Fortran standard only guarantees
> interoperability between C99's _Bool and Fortran's C_Bool-kind logicals and C99
> defines that true has the value 1 and false the value 0. Using any other integer
> value with GNU Fortran's LOGICAL (with any kind parameter) gives an undefined
> result. (Passing other integer values than 0 and 1 to GCC's _Bool is also
> undefined, unless the integer is explicitly or implicitly casted to _Bool.)

What should be added to that?

[Bug fortran/47605] Document that C_Bool might be the wrong constant for C Booleans

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47605

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> > For logical types, please note that the Fortran standard only guarantees
> > interoperability between C99's _Bool and Fortran's C_Bool-kind logicals and C99
> > defines that true has the value 1 and false the value 0. Using any other integer
> > value with GNU Fortran's LOGICAL (with any kind parameter) gives an undefined
> > result. (Passing other integer values than 0 and 1 to GCC's _Bool is also
> > undefined, unless the integer is explicitly or implicitly casted to _Bool.)
>
> What should be added to that?

No answer for over a year. Closing as FIXED.