使用extern关键字的问题 [英] problem using extern keyword

问题描述

我是Win32 API的初学者 我在最近开始的一个小项目中遇到了 extern 关键字的问题。

这是我的一个例子尝试做，错误正在使用 一个简单的代码。

 RESOURCE.H 
 
 extern HWND hwnd; //一切正常，没有"extern" 
 WNDCLASSEX wc; 
 MSG消息; 

 LRESULT CALLBACK WndProc（HWND hwnd，UINT msg，WPARAM wParam，LPARAM lParam） 
 {
 switch（msg）
 {
 
 case WM_DESTROY：
 {
 if（hwnd ==（HWND）GetModuleHandle（NULL） ）
 PostQuitMessage（0）; 
其他
休息; 
} 
休息; 
 
默认值：
返回DefWindowProc（hwnd，msg，wParam，lParam）; 
} 
返回0; 
} 
 
 
 
 int WINAPI WinMain（HINSTANCE hInstance，HINSTANCE hPrevInstance，
 LPSTR lpCmdLine，int nCmdShow）
 {
 
 
 wc.cbSize = sizeof（WNDCLASSEX）; 
 wc.style = 0; 
 wc.lpfnWndProc = WndProc; 
 wc.cbClsExtra = 0; 
 wc.cbWndExtra = 0; 
 wc.hInstance = hInstance; 
 wc.hIcon = LoadIcon（NULL，IDI_APPLICATION）; 
 wc.hCursor = LoadCursor（NULL，IDC_ARROW）; 
 wc.hbrBackground =（HBRUSH）（COLOR_WINDOW + 1）; 
 wc.lpszMenuName = MAKEINTRESOURCE（IDR_MAINMENU）; 
 wc.lpszClassName = g_szClassName; 
 wc.hIconSm = LoadIcon（NULL，IDI_APPLICATION）; 
 
 if（！RegisterClassEx（& wc））
 {
 MessageBox（NULL，" Window Registration Failed！"，" Error！"，
 MB_ICONEXCLAMATION | MB_OK）; 
返回0; 
} 
 
 
 hwnd = CreateWindowEx（
 0，
 g_szClassName，
" theForger's Tutorial Application"，
 WS_OVERLAPPEDWINDOW | WS_CLIPCHILDREN，
 CW_USEDEFAULT，CW_USEDEFAULT，480,320，
 NULL，NULL，hInstance，NULL）; 
 
 if（hwnd == NULL）
 {
 MessageBox（NULL，"Window Creation Failed！"，"Error！"，
 MB_ICONEXCLAMATION | MB_OK）; 
返回0; 
} 
 
 g_hMainWindow = hwnd; 
 
 ShowWindow（hwnd，nCmdShow）; 
 UpdateWindow（hwnd）; 
 
 while（GetMessage（& Msg，NULL，0,0）> 0）
 {
 TranslateMessage（& Msg）; 
 DispatchMessage（& Msg）; 
} 
返回Msg.wParam; 
} 

我得到一个"对hwnd的未确定引用"即使我在main.c中包含resource.h

在我的项目中，我实际上想要在另一个模块中访问此句柄，这就是我将其声明为extern的原因

对不起，如果这是错误的地方

感谢您的帮助

解决方案

我在http://www.gamedev.net/topic/366118-file-scope-extern/找到答案

Hi,

I am a beginner in Win32 API  and I am having a problem with extern keyword in a small project I recently started.

Here is an example of what I am trying to do and the error am getting using  a simple code.

RESOURCE.H

extern HWND hwnd; // Everything works fine without "extern"
WNDCLASSEX wc;
MSG Msg;

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
	switch(msg)
	{

		case WM_DESTROY:
		{
          if(hwnd == (HWND)GetModuleHandle(NULL))
		  PostQuitMessage(0);
		  else
		     break;
		}
		break;

		default:
			return DefWindowProc(hwnd , msg , wParam, lParam);
	}
	return 0;
}



int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
	LPSTR lpCmdLine, int nCmdShow)
{


	wc.cbSize		 = sizeof(WNDCLASSEX);
	wc.style		 = 0;
	wc.lpfnWndProc	 = WndProc;
	wc.cbClsExtra	 = 0;
	wc.cbWndExtra	 = 0;
	wc.hInstance	 = hInstance;
	wc.hIcon		 = LoadIcon(NULL, IDI_APPLICATION);
	wc.hCursor		 = LoadCursor(NULL, IDC_ARROW);
	wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
	wc.lpszMenuName  = MAKEINTRESOURCE(IDR_MAINMENU);
	wc.lpszClassName = g_szClassName;
	wc.hIconSm		 = LoadIcon(NULL, IDI_APPLICATION);

	if(!RegisterClassEx(&wc))
	{
		MessageBox(NULL, "Window Registration Failed!", "Error!",
			MB_ICONEXCLAMATION | MB_OK);
		return 0;
	}


	hwnd = CreateWindowEx(
		0,
		g_szClassName,
		"theForger's Tutorial Application",
		WS_OVERLAPPEDWINDOW | WS_CLIPCHILDREN,
		CW_USEDEFAULT, CW_USEDEFAULT, 480, 320,
		NULL, NULL, hInstance, NULL);

	if(hwnd == NULL)
	{
		MessageBox(NULL, "Window Creation Failed!", "Error!",
			MB_ICONEXCLAMATION | MB_OK);
		return 0;
	}

	g_hMainWindow = hwnd;

	ShowWindow(hwnd, nCmdShow);
	UpdateWindow(hwnd);

	while(GetMessage(&Msg, NULL, 0, 0) > 0)
	{
			TranslateMessage(&Msg);
			DispatchMessage(&Msg);
	}
	return Msg.wParam;
}

I get an "Undifined reference to hwnd" even though I included resource.h in my main.c

In my project i actually want to access this handle in another module and that's the reason I declared it as extern

Sorry if this is the wrong place to put this

Thanks for your help

解决方案

I found an answer at : http://www.gamedev.net/topic/366118-file-scope-extern/

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