| re: Extending stl::list???
"David Hilsee" <davidhilseenews@yahoo.com> wrote in message
news:DOqdnUp9kd9W1ZDfRVn-tQ@comcast.com...[color=blue]
> "Barry Hynes" <hynesb@mar.dfo-mpo.gc.ca> wrote in message
> news:uB5Pd.230465$Np3.9557000@ursa-nb00s0.nbnet.nb.ca...[color=green]
>> G'Day folks,
>>
>> Have been working on this problem for quite some time and still no
>> farther
>> ahead. :(
>>
>> Here is my problem...bare with me i am very green :)
>>
>> I have to implement a Safe List, that is derived from the STL class List[/color]
> and[color=green]
>> uses exception handling.
>>
>> From the various FAQ's and newsgroups it says that deriving from STL
>> containers is not wise due to the lack of virtual destructors.
>>
>> Q1.) What is the purpose of this exercise if it is deemed to be poor
>> programming practice?[/color]
>
> I'm guessing that this is an assignment?[/color]
yes
If you're going to be graded on[color=blue]
> this, then I suggest doing what the instructor told you to do, even if it
> is
> considered bad practice.[/color]
this is thru correspondence
Often times, instructors don't care so much about[color=blue]
> the "proper" way of doing things for their assignments. However, you are
> right, public inheritance from standard containers is usually not
> preferred
> because a) they don't have virtual destructors and b) the container is
> publicly accessible, exposing implementation details. For example, one
> could easily bypass your "safe" member functions by simply accessing the
> std::list directly, giving them direct access to "unsafe" functionality
> that
> could cause undefined behavior and preventing you from easily changing the
> way you store elements inside SafeList. This isn't much of a problem with
> private inheritance.
>[color=green]
>> What i invision is a large object (SafeList) that contains my iterators,
>> stl::list and the various methods to work on the list The user
>> constructs/destroys this object
>> in a safe and efficient manner.
>>
>> Q2.)Could you create a wrapper class for STL::List<> and wrap all you
>> iterators and any mutating methods that could produce memory error?...[/color]
>
> Assuming you mean std::list, I don't see why not.
>[color=green]
>> // safeList.h
>>
>> #ifndef SAFELIST_H
>> #define SAFELIST_H
>>
>> #include <list>
>> #include <iterator>
>> #include <memory>
>> #include <stdexcept>
>> using namespace std;
>>
>> typedef list<T> S;
>> typedef list<T>::iterator SI;
>>
>> template<typename T>
>> class SafeList : private S {
>> public:
>> explicit SafeList(const S*);//No no-arg ctor
>> virtual ~SafeList();
>> S* operator->() throw(std::runtime_error);
>> S* operator*() throw(std::runtime_error);
>> //methods ..... //
>> class SafeIterator {
>> public:
>> SafeIterator(const SI*);
>> virtual ~SafeIterator();
>> SI* operator->() throw (std::runtime_error);
>> SI* operator*() throw (std::runtime_error);
>> private:
>> SI* _mySafeIterator;
>> SafeIterator(const SafeIterator&);
>> SafeIterator& operator=(const SafeIterator&);
>> void operator new(size_t) throw (std::bad_alloc);
>> void operator delete(void*) throw();
>> ;
>> private:
>> S* _mySafeList;
>> SafeList(const SafeList&);
>> SafeList& operator = (const SafeList&);
>> ;
>>
>> any help greatly appreciated[/color]
>
>
> The class template doesn't compile and has a few issues (for example, why
> would you have a member list and inherit from it as well?),[/color]
i have no idea...not sure what i am trying to do
but I'm sure you[color=blue]
> were just sketching out an idea in pseudo-C++.[/color]
yes
It's certainly feasible.[color=blue]
> However, as I said before, if this is an assignment, follow the
> instructions
> from the assignment.[/color]
here is the original question
pg 427
Implement a Safe List, that is derived from the STL class List and
uses exception handling.
[color=blue]
>
> --
> David Hilsee
>
>[/color]
thanks for the help
Barry
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