RE: [C++] anonymous struct linkage

["LAMOME Julien CS-SI" <julien dot lamome-cs-si at irsn dot fr>]

a minimum code to show the problem :
toto.F :
      subroutine toto()
      implicit none
      real*8 variable
      common /demof/variable

         print*,'Fortran variable=',variable
      end

toto.cc: 
#include <iostream>
struct {double variable;}demof;
extern "C" void toto();
int main()
{
	demof.variable=3.14159;
	std::cout<<"C++  variable = "<<demof.variable<<std::endl;
	toto();
	return 0;
}

* Gcc 4.1 give me :
C++  variable = 3.14159
 Fortran variable= 3.14159000000000
* Gcc 4.6 give me:
C++  variable = 3.14159
 Fortran variable= 0.00000000000000

Yours differents solutions work, but I would prefer to use an option to have the old behavior. Because, I have 163 files with anonymous strut to modify. And, each file require special attention because struct are linked, or not, with a COMMON, and COMMON are not necessary include in source, etc.
So, if it isn't possible to use an option, I will have a lot of work now. Else I could modify  progressively.

-----Message d'origine-----
De?: Jonathan Wakely [mailto:jwakely.gcc@gmail.com] 
Envoyé?: jeudi 22 novembre 2012 22:07
À?: LAMOME Julien CS-SI
Cc?: gcc-help@gcc.gnu.org
Objet?: Re: [C++] anonymous struct linkage

On 22 November 2012 21:03, Jonathan Wakely wrote:
> On 22 November 2012 15:44, LAMOME Julien CS-SI
> <julien.lamome-cs-si@irsn.fr> wrote:
>> Hi,
>> we have a code mixing C++ and Fortran 77. In fortran, we have some COMMON like :
>> COMMON / DEMOF/VARIABLE
>> Which are include in fortran source file like this :
>> #include <demof.include>
>>
>> We link with C++ code like this :
>> struct { double variable}demof ;
>>
>> The problem is :
>> Between gcc 4.3 and gcc 4.6, the linkage of demof (in C++) change from global to local. This breaks the link between C++ and fortran.
>>
>> How can I restore the global linkage in gcc 4.6 ?
>
> Give the type a name:
>
> struct D { double variable; } demof;
>
> Problem solved.

Alternatively, give it C language linkage:

extern "C" {
  struct { double d; } demof;
}