程序代码：

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    case WM_PAINT:
           {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hWnd, &ps);

         .........
        SYSTEMTIME st;
        GetLocalTime(&st);
        TCHAR cha[9] = {};
        swprintf_s(cha, _T("%hu%hs%hu%hs%hu"), st.wHour, ":", st.wMinute, ":", st.wSecond);
        //InvalidateRect(hWnd, NULL, true);
        DrawText(hdc, cha, -1, &rect, DT_WORDBREAK);
        //Sleep(1000);
                .........
        }
    }
}

[此贴子已经被作者于2023-4-4 08:48编辑过]

程序代码：

#include <SDKDDKVer.h>
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include "resource.h"
#include <cwchar>

RECT g_SysTimeRect = { 0, 0, 100, 50 };
UINT g_SysTimeElapse = 100;
SYSTEMTIME g_SysTime;

LRESULT CALLBACK WndProc( HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam )
{
    switch( message )
    {
    case WM_COMMAND:
        {
            switch( LOWORD(wParam) )
            {
            case IDM_EXIT:
                DestroyWindow(hWnd);
                break;
            default:
                return DefWindowProc(hWnd, message, wParam, lParam);
            }
        }
        break;
    case WM_CREATE:
        SetTimer( hWnd, 1, g_SysTimeElapse, nullptr );
        break;
    case WM_TIMER:
        {
            WORD wHour   = g_SysTime.wHour;
            WORD wMinute = g_SysTime.wMinute;
            WORD wSecond = g_SysTime.wSecond;
            GetLocalTime( &g_SysTime );
            if( wHour!=g_SysTime.wHour || wMinute!=g_SysTime.wMinute || wSecond!=g_SysTime.wSecond )
                InvalidateRect( hWnd, &g_SysTimeRect, FALSE );
        }
        break;
    case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hWnd, &ps);
            {
                wchar_t temp[9] = {};
                swprintf( temp, 9, L"%02hu:%02hu:%02hu", g_SysTime.wHour, g_SysTime.wMinute, g_SysTime.wSecond );
                DrawText( hdc, temp, -1, &g_SysTimeRect, DT_WORDBREAK );
            }
            EndPaint(hWnd, &ps);
        }
        break;
    case WM_DESTROY:
        KillTimer( hWnd, 1 );
        PostQuitMessage( 0 );
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}

int __stdcall wWinMain( HINSTANCE hInstance, HINSTANCE, LPWSTR, int nCmdShow )
{
    WNDCLASSEXW wcex = { 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_VCWIN32));
    wcex.hCursor        = LoadCursor(nullptr, IDC_ARROW);
    wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
    wcex.lpszMenuName   = MAKEINTRESOURCEW(IDC_VCWIN32);
    wcex.lpszClassName  = L"YourWindowClass";
    wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));
    RegisterClassExW( &wcex );

    HWND hWnd = CreateWindowW( L"YourWindowClass", L"YourTitle", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, nullptr, nullptr, hInstance, nullptr );
    if( !hWnd )
        return FALSE;
    ShowWindow( hWnd, nCmdShow );
    UpdateWindow( hWnd );

    HACCEL hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_VCWIN32));

    MSG msg;
    while( GetMessage(&msg,nullptr,0,0) )
    {
        if( !TranslateAccelerator(msg.hwnd,hAccelTable,&msg) )
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
    }
    return (int)msg.wParam;
}