Experimental Physics and
Industrial Control System

Kay-Uwe Kasemir <[email protected]> · Mon, 21 Nov 2005 10:57:16 -0500

On Nov 21, 2005, at 10:37 , Benjamin Franksen wrote:

On Monday 21 November 2005 15:15, Kay-Uwe Kasemir wrote:

The ca_*puser accessors naturally deal with generic (void *),

 ^^^^^^^^^

so you might have to cast to/from (Channel *) or whatever custom type
you plan to park in the user pointer.

Being used to programming languages that properly support polymorphic
types, I find (void*) rather artificial ;-/

Ben's right.
I should be careful with 'naturally'.
Computers and programming languages are
about as artificial as one could get,
nothing natural about them at all.
The 'void *' was, for the lack of a better term,
'generic' in the original ChannelAccess C API,
because C happily assigns 'void *' to/from any
pointer.
C++ is more picky, so you need the additional casts.
Or write your own template wrapper around the 'chid',
with your custom type as the template argument,
to have the user pointer accessible without additional
casts.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System