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how to use c wrapper files in libraries
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Date: 2009-07-21 (13:26)
From: Aaron Bohannon <bohannon@s...>
Subject: Re: [Caml-list] how to use c wrapper files in libraries
I thought so too, but it doesn't work.  ocamlc does pass the option
"-I install" to gcc, but gcc only uses "-I" directories to search for
header files, not object files.  gcc uses "-L" directories to search
for library (".a") files, but this also has no effect on where gcc
looks for ".o" files.

 - Aaron

On Tue, Jul 21, 2009 at 4:48 AM, <> wrote:
> I think that if you install your library along with the obj file, let's say to directory install, and if you pass to ocamlc -I install sndfile.cma ... maybe he will find the obj file and pass it to the linker.
> I didn't do the experimentation though, maybe it won't work.
> Rabih
> -----Message d'origine-----
> De : [] De la part de Aaron Bohannon
> Envoyé : lundi 20 juillet 2009 18:22
> Cc :
> Objet : 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
> warning.
>  - 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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