Commit 87a08d9

[IErrorInfo Interface](http://msdn.microsoft.com/en-us/4dda6909-2d9a-4727-ae0c-b5f90dcfa447)

In classic Win32 programming for C and C++, most functions use Windows-specific typedefs and #define macros (defined in `windef.h`) to specify the types of parameters and return values. These Windows data types are mostly just special names (aliases) given to C/C++ built-in types. For a complete list of these typedefs and preprocessor definitions, see [Windows Data Types](http://msdn.microsoft.com/en-us/4553cafc-450e-4493-a4d4-cb6e2f274d46). Some of these typedefs, such as HRESULT and LCID, are useful and descriptive. Others, such as INT, have no special meaning and are just aliases for fundamental C++ types. Other Windows data types have names that are retained from the days of C programming and 16-bit processors, and have no purpose or meaning on modern hardware or operating systems. There are also special data types associated with the Windows Runtime Library, listed as [Windows Runtime base data types](http://msdn.microsoft.com/en-us/b5735851-ec07-48c1-92b4-ca9f768096f6). In modern C++, the general guideline is to prefer the C++ fundamental types unless the Windows type communicates some additional meaning about how the value is to be interpreted.

In classic Windows programming, libraries are often implemented as COM objects (or more precisely, as COM servers). Many Windows operating system components are implemented as COM servers, and many contributors provide libraries in this form. For information about the basics of COM, see [Component Object Model (COM)](http://msdn.microsoft.com/en-us/3578ca42-a4b6-44b3-ad5b-aeb5fa61f3f4).

The C++ language defines conversions between its fundamental types. It also defines conversions for pointer, reference, and pointer-to-member derived types. These conversions are called "standard conversions." (For more information about types, standard types, and derived types, see [Types](http://msdn.microsoft.com/en-us/6882ee83-ea32-4373-8d57-c3efbbc15af0).)

The second case in which a pointer to a class can be converted to a pointer to a base class is when you use an explicit type conversion. (See [Expressions with Explicit Type Conversions](http://msdn.microsoft.com/en-us/060ad6b4-9592-4f3e-8509-a20ac84a85ae) for more information about explicit type conversions.)

Pointers to type **void** can be converted to pointers to any other type, but only with an explicit type cast (unlike in C). (See [Expressions with Explicit Type Conversions](http://msdn.microsoft.com/en-us/060ad6b4-9592-4f3e-8509-a20ac84a85ae) for more information about type casts.) A pointer to any type can be converted implicitly to a pointer to type **void**.A pointer to an incomplete object of a type can be converted to a pointer to **void** (implicitly) and back (explicitly). The result of such a conversion is equal to the value of the original pointer. An object is considered incomplete if it is declared, but there is insufficient information available to determine its size or base class.

- [Declaration statements](http://msdn.microsoft.com/en-us/14538558-356f-450e-9e1e-3cd62ba952b9). Declarations introduce a name into a program. ([Declarations and Definitions](declarations-and-definitions-cpp.md) provides more detailed information about declarations.)