How to: Hold Object Reference in Unmanaged Memory
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The latest version of this topic can be found at How to: Hold Object Reference in Unmanaged Memory.
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();
}
StringWrapper::x == ManagedString
Example
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();
}
StringWrapper::m_handle == ManagedString