Calling OCaml from C - nothing shown on stdout

[Andreas Sommer <AndiDog@web.de>]

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Hi everybody,

I'm trying to call a OCaml function from C code. This is the OCaml file:

    open Printf

    let hello () =
        Printf.fprintf stdout "%s" "test"
       
    let () =
        let oc = open_out "/tmp/testfile" in
        Printf.fprintf oc "test";
        close_out oc;
       
        Printf.fprintf stdout "Caml main function\n";
       
        Callback.register "Hello callback" hello;
       
        Printf.fprintf stdout "%s" "Finished with OCaml initialization"
    ;;


and this is the C file:

    #include <stdio.h>
    #include <caml/memory.h>
    #include <caml/mlvalues.h>
    #include <caml/callback.h>

    void helloWrapper()
    {
        static value *closure_f = NULL;

        if(closure_f == NULL)
        {
            printf("1\n");
            closure_f = caml_named_value("Hello callback");
            printf("2\n");
            printf("Closure pointer: %p\n", closure_f);
        }
        printf("3\n");
        caml_callback(*closure_f, Val_unit);
    }

    int main(int argc, char **argv)
    {
        caml_main(argv);

        printf("calling wrapper\n");
        helloWrapper();

        printf("Done.");
        return 0;
    }


Everything seems to work: The file "/tmp/testfile" is created correctly
(so the OCaml function did get called), and the C program ends with
"Done.", *but* nothing is printed from the OCaml fprintf functions.

I am linking the executable with

    $(OCAMLOPT) -output-obj test.ml -o test_obj.o
    $(CC) -c linkwiththis.c -o linkwiththis.o -I"`$(OCAMLC) -where`"
    $(CC) linkwiththis.o test_obj.o $(NATIVECCLIBS) -lasmrun -o
    camltestprogram -L"`$(OCAMLC) -where`"


What am I doing wrong - how can I make OCaml print to stdout correctly?

Best regards,
    Andreas

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