windows - What does #defining WIN32_LEAN_AND_MEAN exclude exactly?

Question

I found the explanation defining WIN32_LEAN_AND_MEAN "reduces the size of the Win32 header files by excluding some of the less frequently used APIs". Somewhere else I read that it speeds up the build process.

So what does WIN32_LEAN_AND_MEAN exclude exactly? Should I care about this pre-processor directive? Does it speed up the build process?

I've also seen a pre-processor directive in projects named something along the lines of extra lean. Is this another esoteric pre-processor incantation I should know about?

Answer 1

Directly from the Windows.h header file:

#ifndef WIN32_LEAN_AND_MEAN
    #include <cderr.h>
    #include <dde.h>
    #include <ddeml.h>
    #include <dlgs.h>
    #ifndef _MAC
        #include <lzexpand.h>
        #include <mmsystem.h>
        #include <nb30.h>
        #include <rpc.h>
    #endif
    #include <shellapi.h>
    #ifndef _MAC
        #include <winperf.h>
        #include <winsock.h>
    #endif
    #ifndef NOCRYPT
        #include <wincrypt.h>
        #include <winefs.h>
        #include <winscard.h>
    #endif

    #ifndef NOGDI
        #ifndef _MAC
            #include <winspool.h>
            #ifdef INC_OLE1
                #include <ole.h>
            #else
                #include <ole2.h>
            #endif /* !INC_OLE1 */
        #endif /* !MAC */
        #include <commdlg.h>
    #endif /* !NOGDI */
#endif /* WIN32_LEAN_AND_MEAN */

If you want to know what each of the headers actually do, typing the header names into the search in the MSDN library will usually produce a list of the functions in that header file.

Also, from Microsoft's support page:

To speed the build process, Visual C++ and the Windows Headers provide the following new defines:

VC_EXTRALEAN
WIN32_LEAN_AND_MEAN

You can use them to reduce the size of the Win32 header files.

Finally, if you choose to use either of these preprocessor defines, and something you need is missing, you can just include that specific header file yourself. Typing the name of the function you're after into MSDN will usually produce an entry which will tell you which header to include if you want to use it, at the bottom of the page.