[C++]VC中预编译的头文件放那里？

用C++写程序，肯定要用预编译头文件，就是那个stdafx.h.
不过我一直以为只要在.cpp文件中包含stdafx.h 就使用了预编译头文件，其实不对。

在VC++中，预编译头文件是指放到stdafx.h中的头文件才会有效果。
如下：

file: stdafx.h

// stdafx.h : include file for standard system include files,
// or project specific include files that are used frequently, but
// are changed infrequently
//

#pragma once

#ifndef _WIN32_WINNT        // Allow use of features specific to Windows XP or later.                   
#define _WIN32_WINNT 0x0501    // Change this to the appropriate value to target other versions of Windows.
#endif                        

#define WIN32_LEAN_AND_MEAN        // Exclude rarely-used stuff from Windows headers

// 各位注意，要想使用预编译效果的头文件要放这里。
#include <Windows.h>
#include "xxx.h"

// TODO: reference additional headers your program requires here

在stdafx.cpp中保持不变即可，默认如下：

// stdafx.cpp : source file that includes just the standard includes
// CPPTestHelper.pch will be the pre-compiled header
// stdafx.obj will contain the pre-compiled type information

#include "stdafx.h"

// TODO: reference any additional headers you need in STDAFX.H
// and not in this file