While doing some programming using C++/CLI for .NET interop, I ran across this compiler error:

error C2872: ‘IServiceProvider’ : ambiguous symbol

As the MSDN reference indicates, the compiler can’t sort out a symbol because it encountered multiple definitions. In this case it was because of a core IServiceProvider definition that was not part of my code.

Rules to avoid this error:

• Do not put “using namespace” statements in global scope in your header files
• If you put “using namespace” statements in your cpp files, add them after any includes

Do not put “using namespace” statements in global scope in your header files

If you put using namespace declarations at the top of a header file, they are global and can lead to these ambiguous symbol compile errors.

This means instead of this in a MyClass.h file:

#pragma once

using namespace System;

public ref class MyClass
{
     IntPtr GetMyReference(String^ name);
}

you’ll need to use fully qualified references:

#pragma once

public ref class MyClass
{
     System::IntPtr GetMyReference(System::String^ name);
}

If you put “using namespace” statements in your cpp files, add them after any includes

Your MyClass.cpp file should look like this:

#include "StdAfx.h"
#include "MyClass.h"

using namespace System;

IntPtr MyClass::GetMyReference(String^ name)
{
     // provide implementation
}