[Haskell-cafe] GHCi + FFI + global C variables

[Francisco Vieira de Souza]

Hi Simon! Is it not necessary to show the type of igraph_bool_t
igraphhaskell_initialized like

"int igraph_bool_t igraphhaskell_initialized = 0"?

Success!
Vieira

2012/12/11 Simon Marlow <marlowsd at gmail.com>:
> On 10/12/12 00:11, Nils wrote:
>>
>> I'm currently working with a C library that needs to use/modify global C
>> variables, for example:
>>
>>     igraph_bool_t igraphhaskell_initialized = 0;
>>
>>     int igraphhaskell_initialize()
>>     {
>>       if (igraphhaskell_initialized != 0)
>>       {
>>         printf("C: Not initializing. igraphhaskell_initialized = %i\n",
>> igraphhaskell_initialized);
>>         return 1;
>>       }
>>       // initialization
>>     }
>>
>> If I compile an example programm using this library everything works
>> fine, but if I try to run the same program in GHCi it dies with the
>> message
>>
>>     C: Not initializing. igraphhaskell_initialized = -907777
>>
>> The value (and apparently the adress of the global variable) is
>> completly off, and I have no idea what is causing this or how to solve
>> this issue and make the library GHCi-friendly. Is it possible to run
>> this code in GHCi at all? Also, since it's a foreign library I obviously
>> cannot just change the C code to simply not use any global variables at
>> all.
>
>
> Sounds like it could be this: http://hackage.haskell.org/trac/ghc/ticket/781
>
> Compiling your program with -fPIC should fix it.
>
> Cheers,
>         Simon
>
>
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