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 includes the CLSID variable like const IID xx = {000..-}
It's wrong way to initialize a GUID. Because by directly including the CLSID variable, if many 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 macro DECLSPEC_SELECTANY keyword 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 includes 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.