How to initialize guid

For the details on how to initialize a guid, check this page http://support.microsoft.com/kb/130869. (definitely we are using a new version compiler! So get to use # include <initguid. h>)

Summary of a problem I met and finally find the above solution to totally undertand the case:

Some CPP in our project uses below # include to intialize some guid:

# Include <XX. \... somename. h>

# Include <XX... somename. c> // It variables des the CLSID variable like const IID xx = {000 ..-}

It's wrong way to initialize a guid. Because by directly including the CLSID variable, if your CPPS need the guid and # include this way, Link error:

Error lnk2005: XX object already defined in XXX. obj.

Oh, my!

The correct way to initialize a guid is to # include <initguid. h> before any # include to use a guid.By a macroDeclspec_selectanyKeyword is used in the define_guid macro, which makes sure that the linker will correctly handle this multiple definition.

Note more:

If two CPP in one project # include <test. h>, which has des below:

# Include "stdafx. H"

Int pp = 100;
Class ctest
{

};

Building the project, we will recevie one link error:

Error lnk2005: "int pp "(? PP @ 3ha) already defined

But the class definition will pass. so the conclusion is: if more than one CPPS # include a header file, which happens to define some variable like "int .. ", Link error will be reported while the class definition is OK to use.