Why is #pragma comment(lib, "atlthunk.lib") needed in source file?

TFS

2010-08-26 08:48:03 UTC

I'm trying to use VC++ 2008 Express (in 32bit XP). I'm told to install WDK
7.1.0 in order to get ATL. After installing WDK and making the "build -cZ",
I added all the necessary folder paths for "Include" and "Library" in VC++
2008 Express. More exactly, I went to Tools menu > Options , then in
"Projects and Solutions" branch > "VC++ Directories" sub-branch, I added the
following paths to Include:
* C:\WinDDK\7600.16385.1\inc\atl71
* C:\WinDDK\7600.16385.1\inc\api
* C:\WinDDK\7600.16385.1\inc\mfc42
and the following to Library:
* C:\WinDDK\7600.16385.1\lib\ATL\i386

So far so good, right? Then comes the strange thing that I don't understand.

For some projects which were written in VC++ 2003, 2005 or 2008 (not
express), sometimes I have to add
#pragma comment(lib, "atlthunk.lib")
in source code file, eg in stdafx.h

I understand that this instruction tells the linker to look for atlthunk.lib
file. But why just this file in particular? You see,
C:\WinDDK\7600.16385.1\lib\ATL\i386 contains four lib files:

atl.lib, atls.lib, atlsd.lib and atlthunk.lib.

The other three lib files are loaded correctly without I need to write
something like
#pragma comment(lib, "atl.lib")

Then why does this atlthunk.lib require us to change source code? Is there
any side-effect is the project is opened in VC++ 2008 full edition again?
_______

Technical detail in case you ask why atlthunk.lib is needed:
When atlwin.h or atlcom.h is included and a certain memroy allocation
function is called, this atlthunk.lib is needed.