本文共 24378 字，大约阅读时间需要 81 分钟。

第21章  动态链接库

2.1 关于库的基本知识

Windows程序是可执行文件，通常创建一个或多个窗口，并使用消息循环来接收用户的输入。

动态库一般不能直接执行，而且他们一般也不接收消息。他是包含许多函数的独立文件，这些函数可以被应用程序和其他DLL调用以完成特定的工作。

动态链接发生在运行时，静态链接发生在编译时。

常见动态库KERNEL32.dll, USER32.dll  GDI32.dll 等

动态库为许多应用程序提供函数和资源。扩展名（dll） 可通过LoadLibrary或LoardLibraryEx函数加载。

动态库相比静态库节省磁盘空间（静态链接每个应用都要链接源码，造成资源浪费），当运行多个应用实例的时候动态库节约内存。此外修改了动态库不必重新编译所有使用了库中函数的应用程序。（静态库修改需要重新编译）

21.1.1 库：一词多义

对象库object library  扩展名为.LIB 在link过程中被添加到exe中。  例如LIBC.LIB

导入库是一种特殊形式的对象库。导入库的扩展名也是.LIB 用来解析源代码中库函数的调用。导入库不包含任何代码。他们只给连接器提供信息，以建立.exe文件中用于动态链接的重新定位。例如 KERNEL32.lib   USER32.lib  GDI32.lib

对象库和导入库仅在程序开发时被使用，而动态库则是在运行时使用。 动态库必须在应用程序EXE目录或者系统目录下。否则必须制定详细的绝对路径加载。

21.1.2 一个简单的DLL

EDRLIB.dll (Easy Drawing Routines)

在VS2013中先创建一个Win32 Project命名为 EDRTEST 选择empty project

然后在Solution上右键Add new project 选择Win32 Project 选择DLL 命名为EDRLIB  选择empty project。添加完成的工程如下

首先在EDRLIBproject中添加EDRLIB.c 和EDRLIB.h文件。代码如下

EDRLIB.h

/*		EDRLIB.H header file*/#ifndef _EDRLIB_H_#define _EDRLIB_H_#ifdef __cplusplus#define EXPORT extern "C" __declspec (dllexport)#else#define EXPORT __declspec (dllexport)#endifEXPORT BOOL CALLBACK EdrCenterTextA(HDC, PRECT, PCSTR);EXPORT BOOL CALLBACK EdrCenterTextW(HDC, PRECT, PCWSTR);#ifdef UNICODE#define EdrCenterText EdrCenterTextW#else#define EdrCenterText EdrCenterTextA#endif#endif // _EDRLIB_H_

EDRLIB.c

/*		EDRLIB.c	-- Easy Drawing Routine Library module						(c) Charles Petzold, 1998*/#include <windows.h>#include "edrlib.h"int WINAPI DllMain(HINSTANCE hInstance, DWORD fdwReason, PVOID pvReserved){	return TRUE;}EXPORT BOOL CALLBACK EdrCenterTextA(HDC hdc, PRECT prc, PCSTR pString){	int		iLength;	SIZE	size;	iLength = lstrlenA(pString);	GetTextExtentPoint32A(hdc, pString, iLength, &size);	return TextOutA(hdc, (prc->right - prc->left - size.cx) / 2,		(prc->bottom - prc->top - size.cy) / 2,		pString, iLength);}EXPORT BOOL CALLBACK EdrCenterTextW(HDC hdc, PRECT prc, PCWSTR pString){	int		iLength;	SIZE	size;	iLength = lstrlenW(pString);	GetTextExtentPoint32W(hdc, pString, iLength, &size);	return TextOutW(hdc, (prc->right - prc->left - size.cx) / 2,		(prc->bottom - prc->top - size.cy) / 2,		pString, iLength);}

extern "c" 表示若头文件被C++编译器编译时，按照C语言的方式编译，防止C++编译器对函数名进行调整而导致链接失败。

21.1.3 库的入口和退出点

若库需要实例句柄（例如创建DialogBox）则应该把hInstance作为全局变量来保存。 最后一个是保留参数

fdwReason参数是4个值中的一个，用来说明Windows调用dllMain的原因。

fdwReason 为 DLL_PROCESS_ATTACH表明动态库被映射到一个进程的地址空间。相当于初始化信号 如果初始化成功范围非0值。 返回0表示windows无法运行该程序

fdwReason 为  DLL_PROCESS_DETACH时，意味着这个进程不再需要DLL了。这给库一个自清理的机会。

fdwReason 为 DLL_THREAD_ATTACH 调用时，意味着一个关联的进程创建了一个新的线程。 当该线程终止时，windows会以DLL_THREAD_DETACH调用dllmain

DllMain以参数DLL_THREAD_DETACH被调用时，线程仍然存在。他甚至可以在此过程中发送线程消息。但他不应该再使用PostMessage，因为该线程可能在消息被收取之前就消失了。

21.1.4  测试程序

EDRTEST.c

/*	EDRTEST.c -- Program using EDRLIB dynamic-link library*/#include <windows.h>  #include "edrlib.h"LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow){	static      TCHAR szAppName[] = TEXT("StrProg");	HWND		hwnd;	MSG         msg;	WNDCLASS    wndClass;       //The window Class    	wndClass.style = CS_HREDRAW | CS_VREDRAW;	wndClass.lpfnWndProc = WndProc;// assign the window procedure to windows class.    	wndClass.cbClsExtra = 0;	wndClass.cbWndExtra = 0;	wndClass.hInstance = hInstance;	wndClass.hIcon = LoadIcon(NULL, IDI_APPLICATION);	wndClass.hCursor = LoadCursor(NULL, IDC_ARROW);	wndClass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);	wndClass.lpszMenuName = NULL;	wndClass.lpszClassName = szAppName;	//Register the Window Class to the Windows System.     	if (!RegisterClass(&wndClass))	{		MessageBox(NULL, TEXT("This program require Windows NT!"),			szAppName, MB_ICONERROR);		return 0;	}	//This function will generate an WM_CREATE message.    	hwnd = CreateWindow(szAppName,      //Window class name    		TEXT("DLL Demonstration Program"),      //Window caption    		WS_OVERLAPPEDWINDOW,            //Window Style    		CW_USEDEFAULT,                  //initial x position    		CW_USEDEFAULT,                  //initial y position    		CW_USEDEFAULT,                  //initial x size    		CW_USEDEFAULT,                  //initial y size    		NULL,                           //parent window handle    		NULL,                           //window menu handle    		hInstance,                      //program instance handle    		NULL);                          //creation parameters    	ShowWindow(hwnd, iCmdShow);	UpdateWindow(hwnd); //This function will generate a WM_PAINT message.    	/* The message loop for this program.	if received the WM_QUIT message, the function will return 0.*/	while (GetMessage(&msg, NULL, 0, 0))	{		TranslateMessage(&msg);		DispatchMessage(&msg);	}	return msg.wParam;}//define the Window Procedure WndProc    LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam){	HDC			hdc;	PAINTSTRUCT ps;	RECT		rect;	switch (message) //get the message    	{	case WM_PAINT:		hdc = BeginPaint(hwnd, &ps);		GetClientRect(hwnd, &rect);		EdrCenterText(hdc, &rect,			TEXT("This string was displayed by a DLL"));		EndPaint(hwnd, &ps);		return 0;	case WM_DESTROY:		PostQuitMessage(0);		return 0;	}	return  DefWindowProc(hwnd, message, wParam, lParam);}

1. 右键EDRTEST设置为Active Project

2. 设置依赖关系 Project->Project dependencies. 勾选EDRLIB

表示EDRLIB如果有必要会在EDRTEST之前重新生成。

3. 确保最后生成的DLL和EXE在同一个目录VS2013默认在Solution的Release或者Debug下。不需要修改

4. 在ProjectSetting中，设置EDRTEST的语言为UNICODE （默认不需要修改）

5. 在VS2013中除了设置ProjectDependency以外还需要设定Reference关系。（Dependency只影响编译）

在EDRTEST的Project Setting中  Common Properties中添加References 为 EDRLIB（这部非常关键，否则编译的时候会报告link错误）这样连接器就会自动加载EDRLIB.lib的导入库从而在运行时动态链接EDRLIB.dll文件。

*否则需要自己写Loardlibrary加载dll并自己申明函数指针调用。并且在恰当的时候Freelibrary

运行结果如下。

DLL做的所有事情都代表应用程序的行为。例如所有他分配的内存由应用程序拥有，他所创建的任何窗口都属于应用程序，他所打开的任何文件也属于应用程序。多个进程可以共享DLL中相同的代码，然而由DLL维护的数据对每个进程是不一样的。每个进程都有自己的，供DLL使用数据的地址空间。

21.1.5 在DLL中共享内存

windows默认对于dll的内存访问是进程隔离的（进程间对于同一个DLL不共享内存）

STRPROG程序和STRLIB的例子

STRLIB 中的3个导出函数使用共享内存 用来存储和排序256个字符串。放在共享内存中

EXPORT BOOL CALLBACK AddString (pStringIn) //添加字符串

EXPORT BOOL CALLBACK DeleteString (pStringIn) //删除字符串

EXPORT int CALLBACK GetStrings(pfnGetStrCallBack, pParam) //获取字符串 参数是回调函数

回调函数原型

EXPORT BOOL CALLBACK GetStrCallBack(PSTR pString, PVOID pParam) 每对应一个字符串调用一次call back函数直到返回FALSE。 

项目名字为STRPROG

STRLIB.h

/*		STRLIB.H header file*/#ifdef __cplusplus#define EXPORT extern "C" __declspec (dllexport)#else#define EXPORT __declspec (dllexport)#endif// the maximum number of strings STRLIB will store and their lengths#define MAX_STRINGS 256#define MAX_LENGTH	63// the callback function type definition uses generic stringstypedef BOOL(CALLBACK * GETSTRCB) (PCTSTR, PVOID);// each function has ANSI and UNICODE versionsEXPORT BOOL CALLBACK AddStringA (PCSTR);EXPORT BOOL CALLBACK AddStringW (PCWSTR);EXPORT BOOL CALLBACK DeleteStringA (PCSTR);EXPORT BOOL CALLBACK DeleteStringW (PCWSTR);EXPORT int CALLBACK GetStringsA (GETSTRCB, PVOID);EXPORT int CALLBACK GetStringsW (GETSTRCB, PVOID);// use the correct version depending on the UNICODE identifier#ifdef UNICODE#define AddString		AddStringW#define DeleteString	DeleteStringW#define GetStrings		GetStringsW#else#define AddString		AddStringA#define DeleteString	DeleteStringA#define GetStrings		GetStringsA#endif

/*		STRLIB.c -- Library module for STRPROG program				(c) Charles Petzold, 1998*/#define _CRT_SECURE_NO_WARNINGS#include <windows.h>#include <wchar.h>		// for wide-character string functions#include "strlib.h"// shared memory section (requires /SECTION:shared, RWS in link options)#pragma data_seg ("shared")int	iTotal = 0;WCHAR szStrings[MAX_STRINGS][MAX_LENGTH + 1] = { '\0' };#pragma data_seg ()#pragma comment(linker, "/SECTION:shared,RWS")int WINAPI DllMain(HINSTANCE hInstance, DWORD fdwReason, PVOID pvReserved){	return TRUE;}EXPORT BOOL CALLBACK AddStringA(PCSTR pStringIn){	BOOL	bReturn;	int		iBufSize;	PWSTR	pWideStr;	// convert string to UNICODE and call AddStringW	iBufSize = MultiByteToWideChar(CP_ACP, 0, pStringIn, -1, NULL, 0);	pWideStr = malloc(iBufSize);	MultiByteToWideChar(CP_ACP, 0, pStringIn, -1, pWideStr, iBufSize);	bReturn = AddStringW(pWideStr);	free(pWideStr);	return bReturn;}EXPORT BOOL CALLBACK AddStringW(PCWSTR pStringIn){	PWSTR	pString;	int		i, iLength;	if (iTotal == MAX_STRINGS - 1)		return FALSE;	if ((iLength = wcslen(pStringIn) == 0))		return FALSE;	// allocate memory for storing string, copy it , convert to uppercase	pString = malloc(sizeof(WCHAR) * (1 + iLength));	wcscpy(pString, pStringIn);	_wcsupr(pString);	// alphabetize the strings	for (i = iTotal; i > 0; i--)	{		if (wcscmp(pString, szStrings[i - 1] )>= 0)	//insert sort algorithm			break;		wcscpy(szStrings[i], szStrings[i - 1]);	}	wcscpy(szStrings[i], pString);	iTotal++;	free(pString);	return TRUE;}EXPORT BOOL CALLBACK DeleteStringA(PCSTR pStringIn){	BOOL	bReturn;	int		iBufSize;	PWSTR	pWideStr;	// convert string to UNICODE and call DeleteStringW	iBufSize = MultiByteToWideChar(CP_ACP, 0, pStringIn, -1, NULL, 0);	pWideStr = malloc(iBufSize);	MultiByteToWideChar(CP_ACP, 0, pStringIn, -1, pWideStr, iBufSize);	bReturn = DeleteStringW(pWideStr);	free(pWideStr);	return bReturn;}EXPORT BOOL CALLBACK DeleteStringW(PCWSTR pStringIn){	int i, j;	if (0 == wcslen(pStringIn))		return FALSE;	for (i = 0; i < iTotal; i++)	{		if (_wcsicmp(szStrings[i], pStringIn) == 0)			break;	}	// If given string not in list, return without taking action	if (i == iTotal)		return FALSE;	// else adjust list downward	for (j = i; j < iTotal; j++)		wcscpy(szStrings[j], szStrings[j + 1]);	szStrings[iTotal--][0] = '\0';	return TRUE;}EXPORT int CALLBACK GetStringsA(GETSTRCB pfnGetStrCallBack, PVOID pParam){	BOOL	bReturn;	int		i, iLength;	PSTR	pAnsiStr;	for (i = 0; i < iTotal; i++)	{		// convert string from UNICODE		iLength = WideCharToMultiByte(CP_ACP, 0, szStrings[i], -1, NULL, 0,			NULL, NULL);		pAnsiStr = malloc(iLength);		WideCharToMultiByte(CP_ACP, 0, szStrings[i], -1, pAnsiStr, iLength,			NULL, NULL);		// call callback function		bReturn = pfnGetStrCallBack(pAnsiStr, pParam);		if (bReturn == FALSE)			return i + 1;		free(pAnsiStr);	}	return iTotal;}EXPORT int CALLBACK GetStringsW(GETSTRCB pfnGetStrCallBack, PVOID pParam){	BOOL	bReturn;	int		i;	for (i = 0; i < iTotal; i++)	{		bReturn = pfnGetStrCallBack(szStrings[i], pParam);		if (bReturn == FALSE)			return i + 1;	}	return iTotal;}

STRPROG.c

/*		STRPROG.c - Program using STRLIB dynamic-link library					(c) Charles Petzold, 1998*/#include <windows.h>#include "strlib.h"#include "resource.h"typedef struct{	HDC	hdc;	int xText;	int yText;	int xStart;	int yStart;	int xIncr;	int yIncr;	int xMax;	int yMax;}CBPARAM;LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);TCHAR szAppName[] = TEXT("StrProg");TCHAR szString[MAX_LENGTH + 1];int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow){	HWND		hwnd;	MSG         msg;	WNDCLASS    wndClass;       //The window Class    	wndClass.style = CS_HREDRAW | CS_VREDRAW;	wndClass.lpfnWndProc = WndProc;// assign the window procedure to windows class.    	wndClass.cbClsExtra = 0;	wndClass.cbWndExtra = 0;	wndClass.hInstance = hInstance;	wndClass.hIcon = LoadIcon(NULL, IDI_APPLICATION);	wndClass.hCursor = LoadCursor(NULL, IDC_ARROW);	wndClass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);	wndClass.lpszMenuName = szAppName;	wndClass.lpszClassName = szAppName;	//Register the Window Class to the Windows System.     	if (!RegisterClass(&wndClass))	{		MessageBox(NULL, TEXT("This program require Windows NT!"),			szAppName, MB_ICONERROR);		return 0;	}	//This function will generate an WM_CREATE message.    	hwnd = CreateWindow(szAppName,      //Window class name    		TEXT("DLL Demonstration Program"),      //Window caption    		WS_OVERLAPPEDWINDOW,            //Window Style    		CW_USEDEFAULT,                  //initial x position    		CW_USEDEFAULT,                  //initial y position    		CW_USEDEFAULT,                  //initial x size    		CW_USEDEFAULT,                  //initial y size    		NULL,                           //parent window handle    		NULL,                           //window menu handle    		hInstance,                      //program instance handle    		NULL);                          //creation parameters    	ShowWindow(hwnd, iCmdShow);	UpdateWindow(hwnd); //This function will generate a WM_PAINT message.    	/* The message loop for this program.	if received the WM_QUIT message, the function will return 0.*/	while (GetMessage(&msg, NULL, 0, 0))	{		TranslateMessage(&msg);		DispatchMessage(&msg);	}	return msg.wParam;}BOOL CALLBACK DlgProc(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam){	switch (message)	{	case WM_INITDIALOG:		SendDlgItemMessage(hDlg, IDC_STRING, EM_LIMITTEXT, MAX_LENGTH, 0);		return TRUE;	case WM_COMMAND:		switch (wParam)		{		case IDOK:			GetDlgItemText(hDlg, IDC_STRING, szString, MAX_LENGTH);			EndDialog(hDlg, TRUE);			return TRUE;		case IDCANCEL:			EndDialog(hDlg, FALSE);			return TRUE;		}	}	return FALSE;}BOOL CALLBACK GetStrCallBack(PTSTR pString, CBPARAM * pcbp){	TextOut(pcbp->hdc, pcbp->xText, pcbp->yText, 		pString, lstrlen(pString));	if ((pcbp->yText += pcbp->yIncr) > pcbp->yMax)	{		pcbp->yText = pcbp->yStart;		if ((pcbp->xText += pcbp->xIncr) > pcbp->xMax)			return FALSE;	}	return TRUE;}//define the Window Procedure WndProc    LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam){	static HINSTANCE	hInst;	static int			cxChar, cyChar, cxClient, cyClient;	static UINT			iDataChangeMsg;	CBPARAM				cbparam;	HDC					hdc;	PAINTSTRUCT			ps;	TEXTMETRIC			tm;	switch (message) //get the message    	{	case WM_CREATE:		hInst = ((LPCREATESTRUCT)lParam)->hInstance;		hdc = GetDC(hwnd);		GetTextMetrics(hdc, &tm);		cxChar = (int)tm.tmAveCharWidth;		cyChar = (int)(tm.tmHeight + tm.tmExternalLeading);		ReleaseDC(hwnd, hdc);		//Register message for notifying instances of data changes		iDataChangeMsg = RegisterWindowMessage(TEXT("StrProgDataChange"));		return 0;	case WM_COMMAND:		switch (wParam)		{		case IDM_ENTER:			if (DialogBox(hInst, TEXT("EnterDlg"), hwnd, &DlgProc))			{				if (AddString(szString))					PostMessage(HWND_BROADCAST, iDataChangeMsg, 0, 0);				else					MessageBeep(0);			}			break;		case IDM_DELETE:			if (DialogBox(hInst, TEXT("DeleteDlg"), hwnd, &DlgProc))			{				if (DeleteString(szString))					PostMessage(HWND_BROADCAST, iDataChangeMsg, 0, 0);				else					MessageBeep(0);			}			break;		}		return 0;	case WM_SIZE:		cxClient = (int)LOWORD(lParam);		cyClient = (int)HIWORD(lParam);		return 0;	case WM_PAINT:		hdc = BeginPaint(hwnd, &ps);		cbparam.hdc = hdc;		cbparam.xText = cbparam.xStart = cxChar;		cbparam.yText = cbparam.yStart = cyChar;		cbparam.xIncr = cxChar * MAX_LENGTH;		cbparam.yIncr = cyChar;		cbparam.xMax = cbparam.xIncr * (1 + cxClient / cbparam.xIncr);		cbparam.yMax = cyChar * (cyClient / cyChar - 1);		GetStrings((GETSTRCB)GetStrCallBack, (PVOID)&cbparam);		EndPaint(hwnd, &ps);		return 0;	case WM_DESTROY:		PostQuitMessage(0);		return 0;	default:		if (message == iDataChangeMsg)			InvalidateRect(hwnd, NULL, TRUE);		break;	}	return  DefWindowProc(hwnd, message, wParam, lParam);}

//{  {NO_DEPENDENCIES}}// Microsoft Developer Studio generated include file.// Used by StrProg.rc//#define IDC_STRING                      1000#define IDM_ENTER                       40001#define IDM_DELETE                      40002#define IDC_STATIC                      -1// Next default values for new objects// #ifdef APSTUDIO_INVOKED#ifndef APSTUDIO_READONLY_SYMBOLS#define _APS_NEXT_RESOURCE_VALUE        104#define _APS_NEXT_COMMAND_VALUE         40003#define _APS_NEXT_CONTROL_VALUE         1001#define _APS_NEXT_SYMED_VALUE           101#endif#endif

//Microsoft Developer Studio generated resource script.//#include "resource.h"#define APSTUDIO_READONLY_SYMBOLS///// Generated from the TEXTINCLUDE 2 resource.//#include "afxres.h"/#undef APSTUDIO_READONLY_SYMBOLS/// English (U.S.) resources#if !defined(AFX_RESOURCE_DLL) || defined(AFX_TARG_ENU)#ifdef _WIN32LANGUAGE LANG_ENGLISH, SUBLANG_ENGLISH_US#pragma code_page(1252)#endif //_WIN32#ifdef APSTUDIO_INVOKED///// TEXTINCLUDE//1 TEXTINCLUDE DISCARDABLE BEGIN    "resource.h\0"END2 TEXTINCLUDE DISCARDABLE BEGIN    "#include ""afxres.h""\r\n"    "\0"END3 TEXTINCLUDE DISCARDABLE BEGIN    "\r\n"    "\0"END#endif    // APSTUDIO_INVOKED///// Dialog//ENTERDLG DIALOG DISCARDABLE  20, 20, 186, 47STYLE DS_MODALFRAME | WS_POPUP | WS_CAPTION | WS_SYSMENUCAPTION "Enter"FONT 8, "MS Sans Serif"BEGIN    LTEXT           "&Enter:",IDC_STATIC,7,7,26,9    EDITTEXT        IDC_STRING,31,7,148,12,ES_AUTOHSCROLL    DEFPUSHBUTTON   "OK",IDOK,32,26,50,14    PUSHBUTTON      "Cancel",IDCANCEL,104,26,50,14ENDDELETEDLG DIALOG DISCARDABLE  20, 20, 186, 47STYLE DS_MODALFRAME | WS_POPUP | WS_CAPTION | WS_SYSMENUCAPTION "Delete"FONT 8, "MS Sans Serif"BEGIN    LTEXT           "&Delete:",IDC_STATIC,7,7,26,9    EDITTEXT        IDC_STRING,31,7,148,12,ES_AUTOHSCROLL    DEFPUSHBUTTON   "OK",IDOK,32,26,50,14    PUSHBUTTON      "Cancel",IDCANCEL,104,26,50,14END///// Menu//STRPROG MENU DISCARDABLE BEGIN    MENUITEM "&Enter!",                     IDM_ENTER    MENUITEM "&Delete!",                    IDM_DELETEEND///// DESIGNINFO//#ifdef APSTUDIO_INVOKEDGUIDELINES DESIGNINFO DISCARDABLE BEGIN    "ENTERDLG", DIALOG    BEGIN        LEFTMARGIN, 7        RIGHTMARGIN, 179        TOPMARGIN, 7        BOTTOMMARGIN, 40    END    "DELETEDLG", DIALOG    BEGIN        LEFTMARGIN, 7        RIGHTMARGIN, 179        TOPMARGIN, 7        BOTTOMMARGIN, 40    ENDEND#endif    // APSTUDIO_INVOKED#endif    // English (U.S.) resources/#ifndef APSTUDIO_INVOKED///// Generated from the TEXTINCLUDE 3 resource.///#endif    // not APSTUDIO_INVOKED

开了两个窗口分别加入string， 两个窗口的string分别都可以显示出来。而且都可以对其进行增删操作。如果所有调用此dll的进程都退出，则共享内存的空间会被释放

注：经过测试发现如果将两个dll和exe分别放置在不同的目录下，发现两个strprog之间不能通过dll共享内存了。怀疑是windows操作系统加载了两份dll？

难道windows操作系统是根据目录文件名的方式来判断dll是否已经加载了？后续深入了解崽揭晓。

这里在调试的时候遇到了窗口无法显示的问题CreateWindow会调用默认主窗口函数并发送几条消息，必须返回TRUE才能正常创建窗口。

若使用自定义消息的时候要特别注意返回值的问题。默认交给DefWindowProc来返回即可

windows在win32进程的地址空间构造了一堵墙。通常情况下，一个地址空间的数据是私有的，其他进程看不见。STRLIB表明该程序允许在其实例之间共享其数据。

使用共享内存需要用到VS的编译器的扩展命令和link参数

// shared memory section (requires /SECTION:shared, RWS in link options)#pragma data_seg ("shared")int	iTotal = 0;WCHAR szStrings[MAX_STRINGS][MAX_LENGTH + 1] = { '\0' };#pragma data_seg ()#pragma comment(linker, "/SECTION:shared,RWS")

/SECTION:shared,RWS 表明该区具有可读，可写和可共享的属性。 该区的数据运行被所有STRLIB的实力所共享。

采用共享是在应用程序中共享数据的最方便的方式。如果要动态分配共享内存的空间，则应该考虑使用文件映像对象。参考 MSDN的 File Mapping

21.2 关于动态链接库的其他话题

动态库本身不接收消息。但是一个库模块可以调用GetMessage和PeekMessage。库模块调用这些函数从消息队列拿到的消息，其实是调用该库函数的程序的消息。

动态库可以从库文件或者调用他的应用程序文件中加载资源。需要自己的句柄或者应用程序的实例句柄。

在动态库中创建窗口CreateWindow需要一个实例句柄，因为窗口消息仍然是通过应用程序发送的，最好使用应用程序的实例句柄。

由于模态对话框的消息来自程序外的消息循环，因此你可以在动态库中调用DialogBox创建模态对话框。相应的实力句柄可以使用动态库自身的句柄。dialogBox的hwndParent设定为NULL

21.2.1 没有导入函数的动态链接库

GDI函数可以直接调用是因为在程序运行时已经执行了动态链接 GDI32.lib

也可以自己控制何时加载动态库。

typedef BOOL (WINAPI * PFNRECT)(HDC, int, int, int, int);

HANDLE hLibrary

PFNRECT  pfnRectangle

hLibrary = LoadLIbrary(TEXT("GDI32.DLL));

pfnRectangle = (PFNRECT) GetProcAddress(hLibrary, TEXT("Rectangle"));

然后就可以调用pfnRectangle了

使用完毕以后调用

FreeLibrary(hLibrary);

Windows使用引用计数机制，调用LoadLibrary会增加1 ， FreeLibrary 会减1. 如果某动态库的引用计数器为0.windows会把该库从内存中卸载。

21.2.2 资源库

提供资源给其他程序引用。

ShotBit例子

如果没有导出函数的dll库不会创建导入库 lib 。因此不应该让应用程序依赖于dll 否则链接时候会需要导入库。

BITLIB.c

/*			BITLIB.c -- Code entry point for BITLIB dynamic-link library						(c) Charles Petzold, 1998*/#include <windows.h>int WINAPI DllMain(HINSTANCE hInstance, DWORD fdwReason, PVOID pvReserved){	return TRUE;}

BITLIB.rc

//Microsoft Developer Studio generated resource script.//#include "resource.h"#define APSTUDIO_READONLY_SYMBOLS///// Generated from the TEXTINCLUDE 2 resource.//#include "afxres.h"/#undef APSTUDIO_READONLY_SYMBOLS/// English (U.S.) resources#if !defined(AFX_RESOURCE_DLL) || defined(AFX_TARG_ENU)#ifdef _WIN32LANGUAGE LANG_ENGLISH, SUBLANG_ENGLISH_US#pragma code_page(1252)#endif //_WIN32#ifdef APSTUDIO_INVOKED///// TEXTINCLUDE//1 TEXTINCLUDE DISCARDABLE BEGIN    "resource.h\0"END2 TEXTINCLUDE DISCARDABLE BEGIN    "#include ""afxres.h""\r\n"    "\0"END3 TEXTINCLUDE DISCARDABLE BEGIN    "\r\n"    "\0"END#endif    // APSTUDIO_INVOKED///// Bitmap//1                       BITMAP  DISCARDABLE     "bitmap1.bmp"2                       BITMAP  DISCARDABLE     "bitmap2.bmp"3                       BITMAP  DISCARDABLE     "bitmap3.bmp"4                       BITMAP  DISCARDABLE     "bitmap4.bmp"5                       BITMAP  DISCARDABLE     "bitmap5.bmp"6                       BITMAP  DISCARDABLE     "bitmap6.bmp"7                       BITMAP  DISCARDABLE     "bitmap7.bmp"8                       BITMAP  DISCARDABLE     "bitmap8.bmp"9                       BITMAP  DISCARDABLE     "bitmap9.bmp"#endif    // English (U.S.) resources/#ifndef APSTUDIO_INVOKED///// Generated from the TEXTINCLUDE 3 resource.///#endif    // not APSTUDIO_INVOKED

/*	SHOWBIT.c - Shows bitmaps in BITLIB dynamic-link library			(c) Charles Petzold, 1998*/#include <windows.h>LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);TCHAR szAppName[] = TEXT("ShowBit");int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow){	HWND		hwnd;	MSG         msg;	WNDCLASS    wndClass;       //The window Class    	wndClass.style = CS_HREDRAW | CS_VREDRAW;	wndClass.lpfnWndProc = WndProc;// assign the window procedure to windows class.    	wndClass.cbClsExtra = 0;	wndClass.cbWndExtra = 0;	wndClass.hInstance = hInstance;	wndClass.hIcon = LoadIcon(NULL, IDI_APPLICATION);	wndClass.hCursor = LoadCursor(NULL, IDC_ARROW);	wndClass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);	wndClass.lpszMenuName = NULL;	wndClass.lpszClassName = szAppName;	//Register the Window Class to the Windows System.     	if (!RegisterClass(&wndClass))	{		MessageBox(NULL, TEXT("This program require Windows NT!"),			szAppName, MB_ICONERROR);		return 0;	}	//This function will generate an WM_CREATE message.    	hwnd = CreateWindow(szAppName,      //Window class name    		TEXT("Show Bitmaps from BITLIB (Press Key)"),      //Window caption    		WS_OVERLAPPEDWINDOW,            //Window Style    		CW_USEDEFAULT,                  //initial x position    		CW_USEDEFAULT,                  //initial y position    		CW_USEDEFAULT,                  //initial x size    		CW_USEDEFAULT,                  //initial y size    		NULL,                           //parent window handle    		NULL,                           //window menu handle    		hInstance,                      //program instance handle    		NULL);                          //creation parameters    	ShowWindow(hwnd, iCmdShow);	UpdateWindow(hwnd); //This function will generate a WM_PAINT message.    	/* The message loop for this program.	if received the WM_QUIT message, the function will return 0.*/	while (GetMessage(&msg, NULL, 0, 0))	{		TranslateMessage(&msg);		DispatchMessage(&msg);	}	return msg.wParam;}void DrawBitmap(HDC hdc, int xStart, int yStart, HBITMAP hBitmap){	BITMAP	bm;	HDC		hMemDC;	POINT	pt;	hMemDC = CreateCompatibleDC(hdc);	SelectObject(hMemDC, hBitmap);	GetObject(hBitmap, sizeof(BITMAP), &bm);	pt.x = bm.bmWidth;	pt.y = bm.bmHeight;	BitBlt(hdc, xStart, yStart, pt.x, pt.y, hMemDC, 0, 0, SRCCOPY);	DeleteDC(hMemDC);}//define the Window Procedure WndProc    LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam){	static HINSTANCE	hLibrary;	static int			iCurrent = 1;	HBITMAP				hBitmap;	HDC					hdc;	PAINTSTRUCT			ps;	switch (message) //get the message    	{	case WM_CREATE:		if ((hLibrary = LoadLibrary(TEXT("BITLIB.DLL"))) == NULL)		{			MessageBox(hwnd, TEXT("Cant't load BITLIB.DLL"),				szAppName, 0);			return -1;		}		return 0;	case WM_CHAR:		if (hLibrary)		{			iCurrent++;			InvalidateRect(hwnd, NULL, TRUE);		}		return 0;	case WM_PAINT:		hdc = BeginPaint(hwnd, &ps);		if (hLibrary)		{			hBitmap = LoadBitmap(hLibrary, MAKEINTRESOURCE(iCurrent));			if (!hBitmap)			{				iCurrent = 1;				hBitmap = LoadBitmap(hLibrary, MAKEINTRESOURCE(iCurrent));			}			if (hBitmap)			{				DrawBitmap(hdc, 0, 0, hBitmap);				DeleteObject(hBitmap);			}		}		EndPaint(hwnd, &ps);		return 0;	case WM_DESTROY:		if (hLibrary)			FreeLibrary(hLibrary);		PostQuitMessage(0);		return 0;	}	return  DefWindowProc(hwnd, message, wParam, lParam);}

在WM_CREATE消息中加载库，若失败则程序直接退出。

在处理WM_DESTROY消息中调用FreeLibrary释放动态库的实力句柄