win32创建空白窗口

#ifndef UNICODE
#define UNICODE
#endif 

#include <windows.h>

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine, int nCmdShow)
{
	// Register the window class.
	const wchar_t CLASS_NAME[] = L"Sample Window Class";

	WNDCLASS wc = {};

	wc.lpfnWndProc = WindowProc;
	wc.hInstance = hInstance;
	wc.lpszClassName = CLASS_NAME;

	RegisterClass(&wc);

	// Create the window.

	HWND hwnd = CreateWindowEx(
		0,                              // Optional window styles.
		CLASS_NAME,                     // Window class
		L"Learn to Program Windows",    // Window text
		WS_OVERLAPPEDWINDOW,            // Window style

										// Size and position
		CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,

		NULL,       // Parent window    
		NULL,       // Menu
		hInstance,  // Instance handle
		NULL        // Additional application data
	);

	if (hwnd == NULL)
	{
		return 0;
	}

	ShowWindow(hwnd, nCmdShow);

	// Run the message loop.

	MSG msg = {};
	while (GetMessage(&msg, NULL, 0, 0))
	{
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}

	return 0;
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
	switch (uMsg)
	{
	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;

	case WM_PAINT:
	{
		PAINTSTRUCT ps;
		HDC hdc = BeginPaint(hwnd, &ps);
		FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW + 1));

		EndPaint(hwnd, &ps);
	}
	return 0;

	}
	return DefWindowProc(hwnd, uMsg, wParam, lParam);
}

#ifndef UNICODE
#define UNICODE
#endif 

使用Unicode

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

声明消息处理函数

const wchar_t CLASS_NAME[] = L"Sample Window Class";

	WNDCLASS wc = {};

	wc.lpfnWndProc = WindowProc;
	wc.hInstance = hInstance;
	wc.lpszClassName = CLASS_NAME;

	RegisterClass(&wc);

在创建一个窗口之前需要先注册，WNDCLASS是一个结构体，参数传递完成后调用RegisterClass()向操作系统注册窗口:操作系统分配一块内存

    HWND hwnd = CreateWindowEx(
		0,                              // Optional window styles.
		CLASS_NAME,                     // Window class
		L"Learn to Program Windows",    // Window text
		WS_OVERLAPPEDWINDOW,            // Window style

										// Size and position
		CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,

		NULL,       // Parent window    
		NULL,       // Menu
		hInstance,  // Instance handle
		NULL        // Additional application data
	);
	
	if (hwnd == NULL)
	{
		return 0;
	}
	
	ShowWindow(hwnd, nCmdShow);

CreateWindowEx()创建成功返回一个窗口句柄，失败返回NULL,ShowWindow()显示窗口

    MSG msg = {};
	while (GetMessage(&msg, NULL, 0, 0))
	{
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}

GetMessage()来从消息队列中获取消息,TranslateMessage()将虚拟键消息转换为字符消息。DispatchMessage()该函数取出一个消息给消息处理函数。

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
	switch (uMsg)
	{
	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;

	case WM_PAINT:
	{
		PAINTSTRUCT ps;
		HDC hdc = BeginPaint(hwnd, &ps);
		FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW + 1));

		EndPaint(hwnd, &ps);
	}
	return 0;

	}
	return DefWindowProc(hwnd, uMsg, wParam, lParam);
}

Windows通过一组定义的 uMesg 来通知函数是什么消息，
通过switch根据消息来选择需要执行的操作。如果不处理此消息使用return DefWindowProc()让操作系统来处理此消息

    case WM_DESTROY:
		PostQuitMessage(0);
		return 0;

当用户单击关闭按钮或按下alt+F4时操作系统发送VM_DESTROY消息,PostQuitMessage(0)销毁窗口

    case WM_PAINT:
	{
		PAINTSTRUCT ps;
		HDC hdc = BeginPaint(hwnd, &ps);
		FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW + 1));

		EndPaint(hwnd, &ps);
	}

• 当窗口显示区域的一部分显示内容或者全部变为“无效”，以致于必须“更新画面”时，将由这个消息通知程序。PAINTSTRUCT该结构体包含了某应用程序用来绘制它所拥有的窗口客户区所需要的信息。
• BeginPaint()函数为指定窗口进行绘图工作的准备，并用将和绘图有关的信息填充到一个PAINTSTRUCT结构中。
• FillRect()填充窗口，(HBRUSH)(COLOR_WINDOW + 1)为填充颜色
• EndPaint()与BeginPaint()对应,结束绘图