From: Rick DeNatale <rick.denatale@...>
Date: 2008-05-05T12:29:22+09:00
Subject: Re: Help with rb_iv_set

On Sun, May 4, 2008 at 11:13 PM, Bryan Richardson
<btrichardson@gmail.com> wrote:
> Hello all,
>
>  I'm trying to use rb_iv_set to set a double value in a C extension I'm
>  writing.
>
>  rb_iv_set(self, "@voltage", 1.01);
>
>  This doesn't seem to work, as I get a '0' instead of '1.01'.  If I use
>  rb_float_new(1.01), then it works.  However, the voltage value in my C
>  structure is a double, and rb_double_new doesn't exist.
>
>  Any suggestions?

rb_iv_set needs a VALUE for the third parameter.
and the value of a Ruby float is a C double:

From the 1.8.6 source:

in ruby.h

VALUE rb_iv_set _((VALUE, const char*, VALUE));

and also:

struct RFloat {
    struct RBasic basic;
    double value;
};

And from numeric.c

VALUE
rb_float_new(d)
    double d;
{
    NEWOBJ(flt, struct RFloat);
    OBJSETUP(flt, rb_cFloat, T_FLOAT);

    flt->value = d;
    return (VALUE)flt;
}


-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/