No I wouldn't think to start adding const to specific fields in a
structure. Certainly not to indicate which members can be updated by
an arbitrary function call.
But why do you us a pointer to pass a struct to a function instead
of passing a copy of the whole struct by value? One of two
reasons...
(1) You want to change elements of the struct and return those
changes to the caller.
(2) As an optimization so that you only push a pointer onto the
stack and not the whole struct. But you have no intention of
changing anything.
The use (or lack) of "const" tells the user about the intent of the
function:
// I am going to change fields in 'response' and return
them to you.
int func(MQTTAsync_responseOptions* response);
// I promise not to change anything in 'response'.
// I'm only using a pointer as an optimization.
int func(const MQTTAsync_responseOptions* response);
Frank
On 05/17/2013 07:01 AM, Ian Craggs
wrote:
Hi Roger,
I don't see why it should be unimportant that a member of a
structure is not const while the structure is const. If the
purpose is to help the writer of a function using the data not to
inadvertently modify caller data, then they are both important.
Maybe I misunderstand the purpose of the suggestion of adding
const to these fields. What do we hope to achieve by doing so, if
not the reason I stated above? And in that case what principle
would we be following in deciding which fields to apply const to,
and which not?
Ian
On 17/05/13 11:43, Roger Light wrote:
Hi Ian,
what about the elements of the
connectOptions, willOptions and SSLOptions
structures, for instance?
Neither SSLOptions nor willOptions are directly exposed in the
external API because they are only used as members of
connectOptions.
connectOptions itself can be const because none of its members
are
modified. My understanding is that it is not important that, for
example, the username member of connectOptions is not const even
though connectOptions may be. Username is mutable but
connectOptions
is not.
Regards,
Roger
_______________________________________________
paho-dev mailing list
paho-dev@xxxxxxxxxxx
http://dev.eclipse.org/mailman/listinfo/paho-dev
_______________________________________________
paho-dev mailing list
paho-dev@xxxxxxxxxxx
http://dev.eclipse.org/mailman/listinfo/paho-dev
|
