issues with interior_ptr pin_ptr

Question

I'm trying to construct a cli/c++ ref class. The purpose of this class is to wrap a native class pointer with some functionality. The native class pointer gets provided to me by a black box factory method. For the life of me I cant figure out how to pin the native pointer so it does not move. Here is the scenario in code(so to speak):

public ref class ManagedFoo{
    private: 
        NativeFooClass* myFoo;
    public:
        ManagedFoo(){
            NativeFooFactory factory();
            NativeFooClass* nativePtr = factory.CreateFoo();
            //here is where i get lost 
            //create a pined pointer to the nativePtr
            pin_ptr<NativeFooClass*> pinPtr = &nativePtr;
            //tring to assign pinPtr to the mamaber var= compilation faliuer 
            myFoo = pinPtr;
        }
}

I keep getting: error C2440: '=' : cannot convert from 'cli::pin_ptr' to 'NativeFooClass*'

I thought the compiler treats them the same? Do i need to static cast? That does not seem right???

The reason I'm trying to pin this pointer is because when I try to use it in a method, and then call this method from C# i get an AccessViolation runtime error "{"Attempted to read or write protected memory. This is often an indication that other memory is corrupt."}"

score 2 · Accepted Answer · edited Apr 13 '17 at 12:40

2

You don't need to. Native objects are stored in memory which is not managed by the .NET garbage collector -- they won't be moved around, and pinning would have no effect.

Simply

    ManagedFoo()
    {
        NativeFooFactory factory; // fixed most-vexing parse
        myFoo = factory.CreateFoo();
    }

should be sufficient.

Or even better

    ManagedFoo()
        : myFoo{NativeFooFactory().CreateFoo()}
    {
    }

UPDATE: Since we find out the object can't outlive its factory,

    ManagedFoo()
        : myFooFactory{new NativeFooFactory()}
        , myFoo{myFooFactory->CreateFoo()}
    {
    }

Although I would suggest some sort of smart pointer to make sure the native objects are correctly freed, perhaps my clr_scoped_ptr.

edited Apr 13 '17 at 12:40

Community

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answered Dec 21 '12 at 17:50

Ben Voigt

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I was under the impression that I need to pin bc when I use the native ptr in a different method i get run time memory error: "Attempted to read or write protected memory. This is often an indication that other memory is corrupt." – Dmitry Dec 21 '12 at 17:55
@Dmitry: Then you need to look at object lifetime, not pinning. Are the objects allowed to live longer than the factory that created them? Right now the factory goes out of scope immediately. – Ben Voigt Dec 21 '12 at 18:24
Ben you were right! The life time of the factory affected the life time of the pointer. – Dmitry Dec 21 '12 at 20:12

issues with interior_ptr pin_ptr

1 Answers1