How to: Hold Object Reference in Native Function
Important This document may not represent best practices for current development, links to downloads and other resources may no longer be valid. Current recommended version can be found here. ArchiveDisclaimer

How to: Hold Object Reference in Native Function 

You can use gcroot.h, which wraps GCHandle, to hold a CLR object reference in unmanaged memory. Alternatively, you can use GCHandle directly.

Example

// hold_object_reference.cpp
// compile with: /clr
#include "gcroot.h"
using namespace System;

#pragma managed
class StringWrapper {

private:
   gcroot<String ^ > x;

public:
   StringWrapper() {
      String ^ str = gcnew String("ManagedString");
      x = str;
   }

   void PrintString() {
      String ^ targetStr = x;
      Console::WriteLine("StringWrapper::x == {0}", targetStr);
   }
};
#pragma unmanaged
int main() {
   StringWrapper s;
   s.PrintString();
}

Output

StringWrapper::x == ManagedString

GCHandle gives you a means to hold a managed object reference in unmanaged memory. You use the Alloc method to create an opaque handle to a managed object and Free to release it. Also, the Target method allows you to obtain the object reference back from the handle in managed code.

// hold_object_reference_2.cpp
// compile with: /clr
using namespace System;
using namespace System::Runtime::InteropServices;

#pragma managed
class StringWrapper {
   IntPtr m_handle;
public:
   StringWrapper() {
      String ^ str = gcnew String("ManagedString");
      m_handle = static_cast<IntPtr>(GCHandle::Alloc(str));
   }
   ~StringWrapper() {
      static_cast<GCHandle>(m_handle).Free();
   }


   void PrintString() {
      String ^ targetStr = safe_cast< String ^ >(static_cast<GCHandle>(m_handle).Target);
      Console::WriteLine("StringWrapper::m_handle == {0}", targetStr);
   }
};

#pragma unmanaged
int main() {
   StringWrapper s; 
   s.PrintString();
}

Output

StringWrapper::m_handle == ManagedString

See Also

Show:
© 2016 Microsoft