QOF iteration and callbacks

[Neil Williams]

On Thursday 17 June 2004 4:22, Derek Atkins wrote:
> Neil Williams <linux at codehelp.co.uk> writes:
>    qof_object_foreach(QOF_TYPE_XXX, book, my_foreach_cb, my_cb_arg);
> Well, DUH, gnc_book_merge_foreach doesn't match the QofEntityForeachCB
> type!  

That's what I can't get straight. I haven't used a lot of callback routines 
before (hazard of being self-taught) and I can't work out how to get the type 
correct.

> Of course this is going to segv, you're passing completely 
> bogus data into your function.

I'd be grateful for an example here. I need to understand the callback and how 
to determine the type required (I think I have that, but need a check) as 
well as how to match that type (my real problem). 

From this snippet:
qof_object_foreach(GNC_ID_INVOICE, testbook,  gnc_bm_foreach, ud);
The doxygen pages for qof_object_foreach give the types for the last two 
parameters as types: QofEntityForeachCB and  gpointer.
what would an empty declaration of gnc_bm_foreach need to look like in order 
to have a compatible pointer and provide access to the object?
void gnc_bm_foreach (QofEntity obj, gpointer ud1); doesn't work. Why?
(yes, I know calling it obj is misleading, it's an artefact of previous 
attempts and is temporary.)

I'm presuming this is a red herring:
void (*gnc_bm_fp) = gnc_bm_foreach;
following a simple function pointer declaration prototype - (nothing to do 
with QOF or Gnucash necessarily) although it compiles, I get the same error 
as when I was using explicit casting - my brain is getting addled, is that 
example a declaration or just another cast?

> > I get:
> > ** CRITICAL **: Error: qof_object_foreach(): No object of type gncInvoice
> > and no debug "foreach running" lines.
>
> See above about the function type being incorrect.  Don't cast it.  The
> cast it biting you in the ass.

:-)

> You're thinking about it too hard.  You're using the right apis but you're
> not using them correctly.  Write your callback function properly.

Help! I'm sorry to have to ask about this but I'm stumped.

-- 

Neil Williams
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