Why I cant return Boost::Scoped_ptr from function?

Question

So I try to create some wrapper around boost.extension functions for class creation. So I have created a function:

template <class BaseClass, class ConstructorType>
 boost::scoped_ptr<BaseClass> get_class (shared_library & lib, std::string class_name, ConstructorType value ) {
map<string, factory<BaseClass, ConstructorType> > lib_factories = get_factories<BaseClass, ConstructorType>(lib);
return boost::scoped_ptr<BaseClass> lib_class(lib_factories[class_name].create(value));
}

which calls :

template <class BaseClass, class ConstructorType>
map<string, factory<BaseClass, ConstructorType> > get_factories (shared_library & lib) {
    type_map lib_types;
    if (!lib.call(lib_types)) {
        cerr << "Types map not found!" << endl;
        cin.get();
    }

    map<string, factory<BaseClass, ConstructorType> > lib_factories(lib_types.get());
    if (lib_factories.empty()) {
        cerr << "Producers not found!" << endl;
        cin.get();
    }
    return lib_factories;
}

but last is not so important. What is important - I can not get my function return=(

I try such way :

boost::scoped_ptr<PublicProducerPrototype> producer = get_class<PublicProducerPrototype, int>(simple_producer, "simpleProducer", 1);

I also have tried :

boost::scoped_ptr<PublicProducerPrototype> producer ( get_class<PublicProducerPrototype, int>(simple_producer, "simpleProducer", 1));

but compiler talls me C2248 it can not call some private member of boost::scoped_ptr<T>

So how to make my return... returnable // how to recieve it?

My guess, without knowing more about the error, is that the copy constructor is private (i.e. the class is intended to be noncopyable) and the return requires making a copy. You're probably not using the right smart pointer for the job. — Steve Howard, Apr 20 '11 at 00:00

score 21 · Accepted Answer · answered Apr 19 '11 at 23:59

21

boost::scoped_ptr is noncopyable. Since you can't copy a scoped_ptr, you can't return one either (returning an object by value requires that you are able to make a copy of it, at least in C++03). If you need to return an object owned by a smart pointer, you need to pick a different type of smart pointer.

If your compiler supports std::unique_ptr you should use that instead (Since it looks like you're using Visual C++, Visual C++ 2010 supports std::unique_ptr); otherwise, consider using std::auto_ptr or {std,std::tr1,boost}::shared_ptr, depending on what your exact use case is.

answered Apr 19 '11 at 23:59

James McNellis

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If you go with `auto_ptr` (which is basically just a broken `unique_ptr`), keep in mind its problems - mainly, that it's not compatible with the STL containers such as `vector` and `map`. Personally, I would recommend `shared_ptr` (which is [part of boost](http://www.boost.org/doc/libs/1_46_1/libs/smart_ptr/smart_ptr.htm)) – BlueRaja - Danny Pflughoeft Apr 20 '11 at 00:07
You can either use `boost::shared_ptr` or `std::auto_ptr`. – James McNellis Apr 20 '11 at 00:07

score 5 · Answer 2 · answered Apr 20 '11 at 02:09

5

You can also try boost::interprocess::unique_ptr.

answered Apr 20 '11 at 02:09

tony

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Why I cant return Boost::Scoped_ptr from function?

2 Answers2