[Bug fortran/84885] c_char bind length

["kargl at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84885

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |kargl at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #1 from kargl at gcc dot gnu.org ---
(In reply to mdblack98 from comment #0)
> subroutine foo(i,c)
>   use, intrinsic :: iso_c_binding, only: c_char
>         integer i
> 
>   type, bind(C) :: params_block
>         character(kind=c_char,len=10) :: c

I see length of 10 here.

>   end type params_block
>         write(*,*) 'X',c,'Z'
> end
> 
> This program fails to compile with gcc 8.0.1 20180304 -- but only if the
> character declaration is inside a type block
> Compiles fine with pre 8.0 compilers
> 
> gfortran -fPIC -g -c foo.f90
> foo.f90:6:42:
> 
>          character(kind=c_char,len=10) :: c
>                                           1
> Error: Component 'c' of BIND(C) type at (1) must have length one

From the F2018 standard,

18.3.2 Interoperability of intrinsic types

Table 18.2 shows the interoperability between Fortran intrinsic
types and C types.  A Fortran intrinsic type with particular type
parameter values is interoperable with a C type if the type and
kind type parameter value are listed in the table on the same row
as that C type.  If the type is character, the length type parameter
is interoperable if and only if its value is one.


C1806 (R726) Each component of a derived type with the BIND
attribute shall be a nonpointer, nonallocatable data component
with interoperable type and type parameters.

Your code is invalid, and the number constraint means
that gfortran must tell you about it.