Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Wed, 27 Jul 2005 16:55:21 -0500

Jeff Hill wrote:

In my example at the meeting I showed how DA could be enhanced to introspect
the structure of the data - w/o an instance of the data. I communicated this
information using an simple template class as follows.

template < class T >

struct TypedVoid

{

};

>

I don't see any reason why the interface to this struct couldn't, or
shouldn't, be extended as Ralph suggested at the meeting, to include member
functions returning type codes for (B) above (it already does A).

Shouldn't a propertySurveyor also be given access rights information

(i.e. whether a particular property is writable or not)? Do you intend

to use a different mechanism to communicate that somehow? Unfortunately

your very clever template mechanism only works with fully symmetrical

property sets; in many cases I think we're going to have to write all

three traverse() routines ourselves, to cope with read-only properties.

WRT (2) above I have no problem using someone else's (Marty's) size locked
type set in the CA protocol, but given the features in DA this would only be
a organizationally cosmetic benefit, but not a feature required to make sure
that the proper size locked type code for what the users is really using is
discovered by CA for its use on the wire. Of course the TypedVoid interface
(or whatever the correct class name is) should use a common type code set.

Can I urge that we make use of the size-locked integer types that are

already defined for us in the C99 header files stdint.h and inttypes.h,

rather than defining our own typedefs and having to check for each

platform whether a long is 32 or 64 bits. There are standard typdefs

for int8_t, int16_t, int32_t, int64_t, uint8_t, uint16_t, uint32_t and

uint64_t. There are other typedefs defined too which might prove

useful, but I won't go into them here.

C99 also defines a matching set of string macros for use in printf() and

scanf() format specifications, which means you can pass an int64_t into

printf() without worrying whether to say "%ld" or "%lld" in the

format string - you use "%" PRId64 instead.

- Andrew
--
Podiabombastic: The tendency to shoot oneself in the foot.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System