Re: Deal with C style function pointer callback in an object

From:
James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Sat, 16 May 2009 01:59:04 -0700 (PDT)
Message-ID:
<ba967551-78e5-48d8-9e6e-64f133788177@s28g2000vbp.googlegroups.com>
On May 16, 8:12 am, Dat Chu <dattan...@gmail.com> wrote:

I want to write an class that hide away the function pointer
callbacks. That is:

Normally i create this function:
void errorCallback(char * err_msg)

then I call
registerErrorCallback(&errorCallback)

Then when there is an error in this third party module, my
errorCallback function will get called.

However, I would like to make this as a clean OO
implementation. I face with a problem, how can I pass a
function to registerErrorCallback that when call will make
some change the state of my object?


If you're defining it, you can either use a pointer to an
abstract base class, requiring the client to derive his callback
from this base class, or you can use something like
boost::function (which IIRC will be in the next version of the
standard).

If you're dealing with an existing C interface, you're stuck.
(But most such interfaces provide an additional void* for user
data---you can use this to pass a pointer to your abstract base
class or functional object.)
`
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