Error 1 error C2664 : 'cannot convert parameter 1 from 'gcroot<T>' to 'System::IO::Stream ^%' [modified]

[KASR1]

I am using C# class library in C++ using C++/CLI mode. I have declared a class member as follows gcroot <> m_objTest; And the following call gives compilation error m_myInterface->GetResults(m_objTest); Error 1 error C2664 : 'cannot convert parameter 1 from 'gcroot<T>' to 'System::IO::Stream ^%' The following is the prototype of GetResults function in C# void GetResults(ref JobResults jobRes); Help me to solve this error.

modified on Monday, June 28, 2010 12:35 AM

[Lost User]

A gcroot is not a System::IO::Stream ^. You need to convert your object into the correct type required by the function.

It's time for a new signature.

[Nish Nishant]

Before passing it to the by-ref function, you need to use a temp variable. Example:

ref class Derived : Base
{
String^ _s;
public:
Derived(String^ s):_s(s){}
};

void Foo(Derived^% derived)
{
derived = gcnew Derived("From Foo");
}

class Native
{
gcroot<Derived^> _derived;

public:
void Bar()
{
_derived = gcnew Derived("Before");
Derived^ tmp = _derived;
Foo(tmp);
_derived = tmp;
}
};

Regards, Nish

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Blog: blog.voidnish.com Most recent article: An MVVM friendly approach to adding system menu entries in a WPF application

[KASR1]

Yes Exactly i did the same. So there is no option to pass gcroot object as reference to other function?

[Nish Nishant]

As far as I know, no. Remember that the by-ref language behavior is implemented at runtime by the CLR whereas the gcroot is an unmanaged wrapper class. So unless the callee is a C++/CLI method expecting a gcroot argument, what you want to do is quite impossible (in my opinion anyway).

Regards, Nish

---

Blog: blog.voidnish.com Most recent article: An MVVM friendly approach to adding system menu entries in a WPF application

[KASR1]

Thanks for your information.