[Caml-list] Calling C from OCaml and data representation question

[Caml-list] Calling C from OCaml and data representation question

[Vasili Galchin]

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Hello,

    I am working on some run-time library project. I
have read in the online "OReilly" book the chapter
where it discusses data representation in particular C
functions, Long_val and Int_val. Is there really the
preferred way to handle data representation issues
from OCaml to C?? The reason I ask is that C is really
very bad about types like "int" and "long", i.e. these
types are not portable. It is really better to use
"unit32", "unit64", etc. If I have a 32 bit entity,
how can I use Long_val and Int_val safely?

Regards, Vasili 

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Re: [Caml-list] Calling C from OCaml and data representation question

[Remi Vanicat]

Vasili Galchin <vasiliocaml@yahoo.com> writes:

> Hello,
>
>     I am working on some run-time library project. I
> have read in the online "OReilly" book the chapter
> where it discusses data representation in particular C
> functions, Long_val and Int_val. Is there really the
> preferred way to handle data representation issues
> from OCaml to C?? The reason I ask is that C is really
> very bad about types like "int" and "long", i.e. these
> types are not portable. It is really better to use
> "unit32", "unit64", etc. If I have a 32 bit entity,
> how can I use Long_val and Int_val safely?

the ocaml specification tell us that an int on a 32 bit platform is
an integer on 31 bit, an int on a 64 bit platform is an integer on 63
bit, and so one. So beware. If you have really a 32 bit entity, may be
you should use the int32 type. There is the "copy_int32" function in
alloc.h and the Int32_val define in mlvalues.h for manipulating them.

-- 
Rémi Vanicat

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