On 10 February 2010 20:20, Christoph Kappel <unexist@dorfelite.net> wrote:

> Hello,
>
> I have some problems calling following C function with a string as
> value:
>
> dbus_bool_t dbus_message_iter_append_basic(DBusMessageIter *iter, int
> type, const void *value)
>
> I attached it via ffi:
>
> attach_function(:dbus_message_iter_append_basic,
>  :dbus_message_iter_append_basic, [ :pointer,
> DBusType, :pointer ], :bool
> )
>
> (DBusType is an enum with the allowed types as integer.)
>
> In C it should look like this and it allows several types casted to
> void:
>
> DBusMessageIter iter;
> char *value = "foobar";
>
> dbus_message_iter_append_basic(&iter, DBUS_TYPE_STRING, &value);

The ruby-ffi equivalent is:

value = FFI::MemoryPointer.from_string("subtle")
ptr = FFI::MemoryPointer.new(:pointer)
ptr.put_pointer(0, value)
dbus_message_iter_append_basic(piter, :type_string, ptr)

i.e. you need to allocate a chunk of native memory to hold the string,
then allocate another bit of native memory to hold the address of that
first native chunk, and pass that in.