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NNTP-Posting-Date: Sat, 03 Feb 2007 13:48:21 -0600
From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: C Interface example
References: <1170526166.831811.237660@h3g2000cwc.googlegroups.com>
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Date: Sat, 03 Feb 2007 13:48:21 -0600
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Date: 2007-02-03T13:48:21-06:00
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> float *vec_addNf(float *, float *, unsigned int);
> Now what would be the most simple and portable way to write
> a vector,ads and vector.adb file? (Specification and body, in case

> reading all that just for an example on interfacing...

  If you want to call an existing C routine, not rewriting it in Ada,
then the literal translation of the calling interface is:

  type p_float is access all interfaces.c.c_float;

  function vec_addNf(va, vb : in p_float; n : in interfaces.c.unsigned)
  return p_float;
  pragma import(C, vec_addNf, "vec_addNf");
  -- Note: Do this if you really have a C calling convention.
  -- If you are running on MS Windows, you probably want "StdCall"
  -- instead of "C"

and then use it like this
  type vectors is array(interfaces.c.unsigned range <>)
    of aliased interfaces.c.c_float;
  va, vb : vectors(1 .. 100);
  trash : p_float;
  ...
  trash := vec_addNf(va(va'first)'unchecked_access,
                     vb(vb'first)'unchecked_access,
                     va'length);

If you were going to be doing a lot of complex calls on va, vb, vc, and vd
you might want instead

N : interfaces.c.unsigned := 123;
va_data, vb_data, vc_data, vd_data : vectors(1 .. N);
va : constant p_float := va_data(va_data'first)'unchecked_access;
vb : constant p_float := vb_data(vb_data'first)'unchecked_access;
vc : constant p_float := vc_data(vc_data'first)'unchecked_access;
vd : constant p_float := vd_data(vd_data'first)'unchecked_access;

so you could write things like

  trash := vec_addNf(vec_addNf(va,vb,N),vec_addNf(vc,vd,N), N);