编译错误（用户定义类型未定义(IUnknown)）编译错误：用户定义类型未定

?? Symptom: When compiling a Visual Basic 6 application the following error is generated when VB encounters the type "IUnknown":

Compiler error: User-defined type not defined

Cause: This error means simply that the VB compiler has encountered a type that it does not recognise. The compiler is assuming this to be a user-defined type because it is not a system defined one.
In the case of IUnknown this error indicates that the VB project is missing a reference to the OLE Automation library.
Remedy: These notes apply specifically to the case where the unknown type is "IUnknown": add the following reference to the project:

C:\WinNT\System32\stdole2.tlb

substitute C:\Windows if using Windows 9x or XP.
These notes have been tested with Visual Basic 6 running under Windows NT and Windows 2000.Symptom:

When compiling a Visual Basic 6 application the following error is generated when VB encounters the type "IUnknown":

Compiler error:
User-defined type not defined

Cause:

This error means simply that the VB compiler has encountered a type that it does not recognise. The compiler is assuming this to be a user-defined type because it is not a system defined one.

In the case of IUnknown this error indicates that the VB project is missing a reference to the OLE Automation library.

Remedy:

These notes apply specifically to the case where the unknown type is "IUnknown": add the following reference to the project:

C:\WinNT\System32\stdole2.tlb

substitute C:\Windows if using Windows 9x or XP.
These notes have been tested with Visual Basic 6 running under Windows NT and Windows 2000.

【编译错误（用户定义类型未定义(IUnknown)）】原网站http://www.cryer.co.uk/brian/mswinswdev/ms_vb_udtnd_iunknown.htm
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