From: Ryan Davis <ryand-ruby@...>
Date: 2011-11-08T17:48:47+09:00
Subject: Re: Compiling Ruby Inline C code - resolving errors

It is generally best to send these types of questions to a more targeted medium, like writing the author directly or filing a support ticket on github.

On Nov 8, 2011, at 00:04 , Martin Hansen wrote:

> I am trying to get this Ruby inline C code http://pastie.org/2825882 to
> work. The code works in vanilla C, but here I get errors and warnings.
> What causes this error?
> 
> ./backtrack_inline.rb:67: error: lvalue required as unary '&' operand

This one took me a bit...

    #define StringValuePtr(v) rb_string_value_ptr(&(v))

and you're using it in:

    char* s = StringValuePtr(rb_iv_get(self, "@seq"));

so you're essentially doing:

    char* s = rb_string_value_ptr(&rb_iv_get(self, "@seq"));

which you can't really do in C.

> Also, why do I get the following error?
> 
> ./backtrack_inline.rb:73: error: too few arguments to function
> 'backtrack'

Because you're passing too few arguments to the function (6 to 7 arity function):

static
 VALUE backtrack(VALUE self, VALUE _ss, VALUE _s, VALUE _p, VALUE _mm, VALUE _ins, VALUE _del)

vs:

    backtrack(ss, s + 1, p + 1, mm - 1, ins, del)))

Since you're not actually using self for anything, there is no reason for this to be a registered method. You might want to add this to the prefix section.

> Inspecting the resulting C code ( http://pastie.org/2826036) I fail to
> see anything wrong with the arguments. But I do also get the following
> warnings:
> 
> ./backtrack_inline.rb:73: warning: passing argument 1 of 'backtrack'
> makes integer from pointer without a cast
> ./backtrack_inline.rb:73: warning: passing argument 2 of 'backtrack'
> makes integer from pointer without a cast
> ./backtrack_inline.rb:73: warning: passing argument 3 of 'backtrack'
> makes integer from pointer without a cast

This is simply because of the above lack of self, I assume.

I changed your code (with the above) like so:

    # above w/ prefixens
    builder.add_static "id_seq", 'rb_intern("@seq")', "ID"

    # in patscan:
    VALUE seq = rb_ivar_get(self, id_seq);
    char* s = StringValuePtr(seq);

and got '14' as the output (off by 1?).