Re: Common Traps for C extensions

Robert Klemme wrote in post #1074390:
> On Mon, Sep 3, 2012 at 1:52 AM, Bernhard Brodowsky
> <[e-mail]> wrote:
>>> and conversion code with extern "C" with a C++ compiler though.
>>
>> I defined a function with two VALUE args and a VALUE return type and I
>> wanted this to be a method with one argument (plus the self Argument)
>> but I always got this error:
>>
>> error: invalid conversion from 'VALUE (*)(VALUE, VALUE) {aka long
>> unsigned int (*)(long unsigned int, long unsigned int)}' to 'VALUE
>> (*)(...) {aka long unsigned int (*)(...)}' [-fpermissive]
>
> As I said, as long as we do not see the code...  I suggest you create
> a http://sscce.org/ and post it.
>
> Cheers
>
> robert

Thanks anyway, but I rewrote everything and I am using Rice now, which 
works much better except that it doesn't automatically handle this 
problem if the user redefines initialize and it is a little cumbersome 
to do a workaround since Rice assumes it defines the initialize method 
itself etc. Maybe I should write this to the Rice developers because I 
guess nobody wants a Segfault if the user redefines initialize.

The smallest code to reproduce my previous looks about like this:

extern "C" {

VALUE encrypt(VALUE self, VALUE key) {
  return qNil;
}

static VALUE Encrypter = qNil;

Init_RubyCrypto() {
  Encrypter = rb_define_class("Encrypter", rb_cObject);
  rb_define_method(Encrypter, "encrypt", encrypt, 2);
}

}

The problem appears to be that rb_define_method takes a function pointer 
with a variable number of arguments, but encrypt has 2 arguments and C 
somehow implicitely casts this while C++ complains. But it doesn't 
matter anyway now since I use Rice now.

Thanks for the help

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