Help with rb_iv_set

[Bryan Richardson]

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?

 

[Rick DeNatale]

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;
}

 

[Bryan Richardson]

[Note: parts of this message were removed to make it a legal post.]

Hi Rick,

So you're saying that by doing it the way I was doing it (using
rb_float_new) I am indeed doing it correctly?

 

[Tim Pease]

Hi Rick,

So you're saying that by doing it the way I was doing it (using
rb_float_new) I am indeed doing it correctly?

To be explicit about your specific case ...

rb_iv_set(self, "@voltage", rb_float_new(1.01));


Blessings,
TwP

 

[Bryan Richardson]

[Note: parts of this message were removed to make it a legal post.]

Perfect... . Thanks Tim!