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| Jesse... |
 Posted: Wed Oct 22, 2008 10:37 pm |
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Guest
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Hi,
I am trying to understand the usage of sequences for variable-length
elements, and things are in fact rather complex, unclear... and vary from
one ORB to the other !
Therefore, I submit the following general questions, for those who are
familiar with the C++ mapping mysteries ;-)
IDL
typedef sequence<T> TSeq;
interface Service {
TSeq list_Ts();
};
with T as a variable-length type.
In my C++ client I get the sequence from the server via:
TSeq_var theSeq = server->list_Ts();
1rst question: which assertions are valid as regards the specification
(assume variable i is a CORBA::ULong) ?
1- T_var theT = theSeq[i];
2- T_var theT;
theT = theSeq[i];
3- T_var theT = (*theSeq)[i];
4- T_var theT;
theT = (*theSeq)[i];
2nd question: Among the valid assertions, what are those where theT takes
memory ownership (thus sharing it with theSeq !), and those where it
performs a deep-copy of the original sequence item ?
Thanks !
JC. |
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| Jon Biggar... |
| Posted: Thu Oct 23, 2008 6:18 am |
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Guest
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Jesse wrote:
IDL
Quote:
typedef sequence<T> TSeq;
interface Service {
TSeq list_Ts();
};
with T as a variable-length type.
In my C++ client I get the sequence from the server via:
TSeq_var theSeq = server->list_Ts();
1rst question: which assertions are valid as regards the specification
(assume variable i is a CORBA::ULong) ?
1- T_var theT = theSeq[i];
2- T_var theT;
theT = theSeq[i];
3- T_var theT = (*theSeq)[i];
4- T_var theT;
theT = (*theSeq)[i];
2nd question: Among the valid assertions, what are those where theT takes
memory ownership (thus sharing it with theSeq !), and those where it
performs a deep-copy of the original sequence item ?
They should all work and should all invoke a deep copy. However, #3 and
#4 are not recommended--using operator *() on a _var actually invokes
the conversion function operator T*() first. That can lead to
accidental memory management problems.
If you want to avoid the deep copy, just do this:
T &theT = theSeq[i];
but of course you'll have to ensure that you don't access the reference
outside of the lifeime of theSeq.
--
Jon Biggar
jon at (no spam) floorboard.com
jon at (no spam) biggar.org
jonbiggar at (no spam) gmail.com |
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| Jon Biggar... |
| Posted: Thu Oct 23, 2008 6:18 am |
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Guest
|
Jesse wrote:
IDL
Quote:
typedef sequence<T> TSeq;
interface Service {
TSeq list_Ts();
};
with T as a variable-length type.
In my C++ client I get the sequence from the server via:
TSeq_var theSeq = server->list_Ts();
1rst question: which assertions are valid as regards the specification
(assume variable i is a CORBA::ULong) ?
1- T_var theT = theSeq[i];
2- T_var theT;
theT = theSeq[i];
3- T_var theT = (*theSeq)[i];
4- T_var theT;
theT = (*theSeq)[i];
2nd question: Among the valid assertions, what are those where theT takes
memory ownership (thus sharing it with theSeq !), and those where it
performs a deep-copy of the original sequence item ?
They should all work and should all invoke a deep copy. However, #3 and
#4 are not recommended--using operator *() on a _var actually invokes
the conversion function operator T*() first. That can lead to
accidental memory management problems.
If you want to avoid the deep copy, just do this:
T &theT = theSeq[i];
but of course you'll have to ensure that you don't access the reference
outside of the lifeime of theSeq.
--
Jon Biggar
jon at (no spam) floorboard.com
jon at (no spam) biggar.org
jonbiggar at (no spam) gmail.com |
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