From: Andreas Haas <Andreas.Haas1@...>
Date: 2006-06-02T09:22:31+09:00
Subject: How to pass const char *vect[] to C via Ruby/DL?

Hi all,

I'm having problems to understand how to build-up  "const char *vect[]"
data for passing to a C function that I wish to call via Ruby/DL:

#  -----------------
int setv(const char *ids[])
{
    while (*ids) {
        printf("setv: %s\n", ids[0]);
       ids++;
    }
}
#  -----------------

My current Ruby program looks like this:

#  -----------------
#!/usr/bin/ruby

require 'dl/import'

def setv(ary)
    setv = $lib['setv', 'IP']
    ids = DL.malloc(DL.sizeof('S')*(ary.size + 1))
    i = 0
    ary.each do |s|
       ids[DL.sizeof('S')*i] = s.to_ptr
       i += 1
    end
    # ids[3] = nil ?
    r,r1 = setv.call(ids.ref)
end

$lib = DL.dlopen('lib.dylib')

setv(["1", "2", "3"])
#  -----------------

but I get a SEGV and it is not complete anyways. Instead of

    ids[DL.sizeof('S')*i] = s.to_ptr

I already tried

   ids[DL.sizeof('S')*i] = s

and other variations I could think of ...

You know: I can imagine there were better means for
passing string vectors to C, yet the C function interface
as such is given.

So any help or hint is greatly appreciated!

Best regards,
Andreas