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how to use c wrapper files in libraries
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Date: 2009-07-20 (16:21)
From: Aaron Bohannon <bohannon@s...>
Subject: Re: [Caml-list] how to use c wrapper files in libraries
Thank you.  This does clarify some things.  Everything works like
clockwork after reworking things this way.

Based on the output of "ocamlc -verbose", it seems that if you pass
"file.o" file to "ocamlc -a", it does nothing except remember the name
"file.o" and pass it to gcc when the OCaml library is later used,
which is a pretty useless and confusing behavior---in general, you
will not be in the same directory that contains "file.o" when you use
the OCaml library and I don't know of any gcc options that will make
gcc look in other directories for object files.  It would seem better
for "ocamlc -a" to ignore ".o" files and display an appropriate

 - Aaron

On Mon, Jul 20, 2009 at 10:58 AM, <> wrote:
> I am not familiar with this specific library.
> In the general approach, you compile your c code, and package it into a library, let's say libA.a
> Then while building your sndfile.cma, you should pass the option
> ocamlc -a -o sndfile.cma -cclib -lA ...
> A caml executable linked with your library will have also libA.a passed in the linking phase.
> Using ocamlc -verbose could give you a hint to which files are missing.
> Hope this helps,
> Rabih
> -----Message d'origine-----
> De : [] De la part de Aaron Bohannon
> Envoyé : lundi 20 juillet 2009 16:28
> À :
> Objet : [Caml-list] how to use c wrapper files in libraries
> Hello,
> I am trying to use the wrapper for libsndfile contributed by Erik de
> Castro Lopo (
> The wrapper code compiles just fine.  And the tests that use the OCaml
> library it builds work just fine.  However, I am having a frustrating
> compile-time error when I try to compile my program in a different
> directory.
> The wrapper code is being packaged into an OCaml library using the
> following command:
> ocamlc -a -o sndfile.cma -custom sndfile_stub.o sndfile.cmo \
>  -ccopt -L/usr/local/lib -cclib -lsndfile
> Within the same directory, the test program can be successfully compiled with:
> ocamlc -o test_sndfile sndfile.cma
> Within a different directory, I used:
> ocamlc -o mytest -I /path/to/libsndfile-ocaml/files/   sndfile.cma
> And I get:
> powerpc-apple-darwin8-gcc-4.0.1: sndfile_stub.o: No such file or directory
> Error while building custom runtime system
> I have tried setting every path-related option I could find, and
> nothing helped.  I tried reading everything I could find about
> compiling and using c wrappers for OCaml, but there is a severe lack
> of documentation on the topic.  In particular, I could find no example
> of a c object file being given as an argument to an "ocamlc -a"
> command, so I am not sure what that is supposed to do, which makes it
> impossible for me to understand this error message.
> I am using OCaml 3.10.1 on OS X 10.4.  Any help would be appreciated.
>  - Aaron
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