错误的程序段：
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{

HDC hdc; PAINTSTRUCT ps; HBRUSH hbrush; /////////////////////// HPEN hpen; static int dispmode = -1; LPCTSTR str; switch (message) {.....} hbrush = (HBRUSH)GetStockObject(DKGRAY_BRUSH); hpen = (HPEN)GetStockObject(BLACK_PEN); SelectObject(hdc, hbrush); ///////////////error：使用了可能未初始化的本地指针变量"hdc"？ SelectObject(hdc, hpen); RoundRect(hdc, 50, 120, 100, 200, 15, 15); EndPaint(hWnd, &ps); return 0;

}

完整代码：
// Win32Project1.cpp : 定义应用程序的入口点。
//

include "stdafx.h"

include "Win32Project1.h"

define MAX_LOADSTRING 100

// 全局变量:
HINSTANCE hInst; // 当前实例
WCHAR szTitle[MAX_LOADSTRING]; // 标题栏文本
WCHAR szWindowClass[MAX_LOADSTRING]; // 主窗口类名

// 此代码模块中包含的函数的前向声明:
ATOM MyRegisterClass(HINSTANCE hInstance);
BOOL InitInstance(HINSTANCE, int);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
INT_PTR CALLBACK About(HWND, UINT, WPARAM, LPARAM);

int APIENTRY wWinMain(_In_ HINSTANCE hInstance,

_In_opt_ HINSTANCE hPrevInstance, _In_ LPWSTR lpCmdLine, _In_ int nCmdShow)

{

UNREFERENCED_PARAMETER(hPrevInstance); UNREFERENCED_PARAMETER(lpCmdLine); // TODO: 在此放置代码。 // 初始化全局字符串 LoadStringW(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING); LoadStringW(hInstance, IDC_WIN32PROJECT1, szWindowClass, MAX_LOADSTRING); MyRegisterClass(hInstance); // 执行应用程序初始化: if (!InitInstance (hInstance, nCmdShow)) { return FALSE; } HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_WIN32PROJECT1)); MSG msg; // 主消息循环: while (GetMessage(&msg, nullptr, 0, 0)) { if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg)) { TranslateMessage(&msg); DispatchMessage(&msg); } } return (int) msg.wParam;

}

//
// 函数: MyRegisterClass()
//
// 目的: 注册窗口类。
//
ATOM MyRegisterClass(HINSTANCE hInstance)
{

WNDCLASSEXW wcex; wcex.cbSize = sizeof(WNDCLASSEX); wcex.style = CS_HREDRAW | CS_VREDRAW; wcex.lpfnWndProc = WndProc; wcex.cbClsExtra = 0; wcex.cbWndExtra = 0; wcex.hInstance = hInstance; wcex.hIcon = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_WIN32PROJECT1)); wcex.hCursor = LoadCursor(nullptr, IDC_ARROW); wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW+1); wcex.lpszMenuName = MAKEINTRESOURCEW(IDC_WIN32PROJECT1); wcex.lpszClassName = szWindowClass; wcex.hIconSm = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL)); return RegisterClassExW(&wcex);

}

//
// 函数: InitInstance(HINSTANCE, int)
//
// 目的: 保存实例句柄并创建主窗口
//
// 注释:
//
// 在此函数中，我们在全局变量中保存实例句柄并
// 创建和显示主程序窗口。
//
BOOL InitInstance(HINSTANCE hInstance, int nCmdShow)
{
hInst = hInstance; // 将实例句柄存储在全局变量中

HWND hWnd = CreateWindowW(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,

CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, nullptr, nullptr, hInstance, nullptr);

if (!hWnd)
{

return FALSE;

}

ShowWindow(hWnd, nCmdShow);
UpdateWindow(hWnd);

return TRUE;
}

//
// 函数: WndProc(HWND, UINT, WPARAM, LPARAM)
//
// 目的: 处理主窗口的消息。
//
// WM_COMMAND - 处理应用程序菜单
// WM_PAINT - 绘制主窗口
// WM_DESTROY - 发送退出消息并返回
//
//
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{

HDC hdc; PAINTSTRUCT ps; HBRUSH hbrush; /////////////////////// HPEN hpen; static int dispmode = -1; LPCTSTR str; switch (message) { case WM_COMMAND: { int wmId = LOWORD(wParam); // 分析菜单选择: switch (wmId) { case IDM_ABOUT: DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About); break; case IDM_EXIT: DestroyWindow(hWnd); break; default: return DefWindowProc(hWnd, message, wParam, lParam); } } break; case WM_LBUTTONDOWN: InvalidateRect(hWnd, nullptr, TRUE); break; case WM_PAINT: hdc = BeginPaint(hWnd, &ps); dispmode = 0; switch (dispmode) { case 0:str = _T(" hi"); SetMapMode(hdc, MM_TEXT); TextOut(hdc, 0, 0, str, _tcsclen(str));break; case 1:str = _T("hi 2"); SetMapMode(hdc, MM_ISOTROPIC); SetWindowExtEx(hdc, 20, 20, nullptr); TextOut(hdc, 0, 0, str, _tcsclen(str));break; } break; case WM_DESTROY: PostQuitMessage(0); break; default: return DefWindowProc(hWnd, message, wParam, lParam); } hbrush = (HBRUSH)GetStockObject(DKGRAY_BRUSH); hpen = (HPEN)GetStockObject(BLACK_PEN); SelectObject(hdc, hbrush); ///////////////error：使用了可能未初始化的本地指针变量"hdc"？ SelectObject(hdc, hpen); RoundRect(hdc, 50, 120, 100, 200, 15, 15); EndPaint(hWnd, &ps); return 0;

}

// “关于”框的消息处理程序。
INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{

UNREFERENCED_PARAMETER(lParam); switch (message) { case WM_INITDIALOG: return (INT_PTR)TRUE; case WM_COMMAND: if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL) { EndDialog(hDlg, LOWORD(wParam)); return (INT_PTR)TRUE; } break; } return (INT_PTR)FALSE;

}

HDC hdc;

switch (message) { // ... case WM_PAINT: hdc = BeginPaint(hWnd, &ps); // ...