Return unmanaged object pointer in C#

Question

I have written two managed C++ wrappers for native C++ classes and I need a unmanaged object of native Class B as a return param in function of managed Wrapper A that construct native Class A!

Example:

// Wrapper A

WrapperA::WrapperA(ClassB *classB)
{
    ClassA *classA = new ClassA(classB);
    ...
}

// native c++
ClassA::ClassA(ClassB *classB)
{
    m_classB = classB; // ClassB *m_classB; in .h
    ...
}

// Wrapper B

ClassB* WrapperB::GetNativeClassB()
{
    return m_classB; // ClassB *m_classB; in .h
}


// in C#
...
WrapperB wrapperB = new WrapperB();

unsafe // need for C++ pointer
{
WrapperA wrapperA = new WrapperA(wrapperB.GetNativeClassB() ); 
// Error: is inaccessible due to its protection level 
// -> is set to public
}
...

Is there a better way without unsafe and why I get an access error ???

Thank you in advance!

greets leon22

Are you sure that both WrapperB::GetNativeClassB and WrapperA::WrapperA are public? — Mike Caron
– Mike Caron, Commented Jul 12, 2011 at 11:40
Constr of Wrapper A/B is public and also GetNativeClassB is set to public — leon22
– leon22, Commented Jul 12, 2011 at 11:50

Marcello Faga · Accepted Answer · 2011-07-12 12:15:13Z

1

Protection level: i'm sure you have public defined, but what about the dll containing the symbol? Are you sure you have the last release?
Unsafe: in order to use/wrap unsafe/native code as C++, the best option it is to use C++/CLI (ex Managed C++), provided starting from the Visual Studio 2005 release. just define a ref class that wraps your native/unmanaged class, that one will be directly accessible from managed code, as C#. Hint to start with Visual Studio: open a new dll CLR project from the Visual C++ section;

C++/CLI is the best solution in my opinion

edited Jul 12, 2011 at 12:15

answered Jul 12, 2011 at 12:05

Marcello Faga

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8 Comments

leon22 Over a year ago

I'm using the classB object already in WrapperB (loading from a dll with GetProcAddress) and it works fine, but returning the object to C# and bypass to WrapperA does not work (due the protection error)

leon22 Over a year ago

And sure the wrappers are written in C++/CLI

Marcello Faga Over a year ago

I think you do not write properly your C++/CLI wrapper classes, because you use unsafe pointer in your wrapper interface (WrapperA(ClassB *classB) ), consequently you need to use the unsafe block. exemple for the contructor of wrapperA-> WrapperA::WrapperA(WrapperB ^classB). use the native pointers only inside the wrapper class

leon22 Over a year ago

I have tested on other way: give the WrapperB with managed ^ as param to WrapperA and then I call wrapperB->GetNativeClassB() -> error: error C3767: candidate function(s) not accessible (method and class are public) I don't understand this (the wrappers are included per add reference in C#)

Marcello Faga Over a year ago

Ok, the last one, i hope it can help you. have you already tried #pragma make_public(ClassB)? msdn.microsoft.com/en-us/library/ms235607%28VS.80%29.aspx.

|

Community · Accepted Answer · 2017-05-23 12:04:16Z

0

Solution from: Pass a C++/CLI wrapper of a native type to another C++/CLI assembly

// in WrapperB
property IntPtr _classB 
{
    IntPtr get() { return IntPtr(classB); }
}

// in WrapperA
ClassB *classB = static_cast<ClassB*>(wrapperB->_classB.ToPointer());
// ... do something ...

edited May 23, 2017 at 12:04

CommunityBot

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answered Jul 13, 2011 at 17:54

leon22

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