BUG: A "C2668: 'InlineIsEqualGUID'" error occurs when you try to build a default ATL project that contains a COM object in Visual C++

Building a default ATL project containing a COM object supporting ISupportErrorInfo might result in the following error: This error may also occur when calling the function InlineIsEqualGUID() in your ATL project.

The problem occurs because the function InlineIsEqualGUID() is defined both in the ATL header file, AtlBase.h, and the Platform SDK header file, Guiddef.h, in different name spaces. The include paths for the build point first to the Platform SDK include directory, and then to the ATL include directory. In the ATL header, InlineIsEqualGUID() is defined in a name space called "ATL", while in the Platform SDK header it is defined in the global name space. Because AtlBase.h includes the statement the compiler is unable to distinguish which definition to use.

To work around this problem, prefix the call to the InlineIsEqualGUID() function with ::ATL::. This explicitly qualifies the ATL namespace from where the implementation of InlineIsEqualGUID is pulled in. For example:

Microsoft has confirmed that this is a bug in the Microsoft products that are listed in the "Applies to" section.

Steps to reproduce the behavior

The following steps are based on Visual C++ 6.0.

1. Create an ATL DLL project and insert a simple object into the project with ISupportErrorInfo support.
2. Make sure that the includes path for the Platform SDK include directory comes before the ATL include directory on the Directories tab of the Options dialog box, which is accessed from the Tools menu.
3. Build the project, and the error message appears.