编写一个基于Win32 API 的时钟程序,显示当前系统日期时间

以下是一个基于Win32 API的时钟程序，可以显示当前系统日期时间：

#include <windows.h>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
                   PSTR szCmdLine, int iCmdShow)
{
    static TCHAR szAppName[] = TEXT("Clock");
    HWND         hwnd;
    MSG          msg;
    WNDCLASS     wndclass;

    wndclass.style         = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc   = WndProc;
    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;

    if (!RegisterClass(&wndclass))
    {
        MessageBox(NULL, TEXT("This program requires Windows NT!"),
                   szAppName, MB_ICONERROR);
        return 0;
    }

    hwnd = CreateWindow(szAppName, TEXT("Clock"),
                        WS_OVERLAPPEDWINDOW | WS_CLIPCHILDREN,
                        CW_USEDEFAULT, CW_USEDEFAULT,
                        CW_USEDEFAULT, CW_USEDEFAULT,
                        NULL, NULL, hInstance, NULL);

    ShowWindow(hwnd, iCmdShow);
    UpdateWindow(hwnd);

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

    return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    static BOOL     f24Hour;
    static HBITMAP  hBitmap;
    static int      cxClient, cyClient;
    static int      cxBitmap, cyBitmap;
    static int      xC, yC, cxC, cyC;
    static int      iRadius, iMarker;
    HDC             hdc, hdcMem;
    PAINTSTRUCT     ps;
    POINT           apt[3];
    SYSTEMTIME      st;
    TCHAR           szBuffer[256];
    int             i, cx, cy, iSec, iMin, iHour, iAngle;
    double          fAngle;

    switch (message)
    {
    case WM_CREATE:
        hdc = GetDC(hwnd);
        hBitmap = LoadBitmap(GetModuleHandle(NULL), TEXT("Clock"));
        hdcMem = CreateCompatibleDC(hdc);
        SelectObject(hdcMem, hBitmap);
        GetObject(hBitmap, sizeof(BITMAP), &bm);
        cxBitmap = bm.bmWidth;
        cyBitmap = bm.bmHeight;
        ReleaseDC(hwnd, hdc);
        DeleteDC(hdcMem);

        SetTimer(hwnd, 1, 1000, NULL);
        f24Hour = TRUE;
        return 0;

    case WM_SIZE:
        cxClient = LOWORD(lParam);
        cyClient = HIWORD(lParam);
        iRadius = min(cxClient, cyClient) / 2.5;
        iMarker = iRadius / 5;
        xC = cxClient / 2;
        yC = cyClient / 2;
        cxC = 7 * iMarker / 4;
        cyC = iMarker / 2;
        return 0;

    case WM_TIMER:
        InvalidateRect(hwnd, NULL, TRUE);
        return 0;

    case WM_PAINT:
        hdc = BeginPaint(hwnd, &ps);

        hdcMem = CreateCompatibleDC(hdc);
        SelectObject(hdcMem, hBitmap);

        BitBlt(hdc, xC - cxBitmap / 2, yC - cyBitmap / 2,
               cxBitmap, cyBitmap, hdcMem, 0, 0, SRCCOPY);

        // Get the current system time.
        GetLocalTime(&st);

        // Convert the time into hour, minute, and second.
        iSec = st.wSecond;
        iMin = st.wMinute;
        if (f24Hour)
            iHour = st.wHour;
        else
            iHour = st.wHour % 12;
        if (iHour == 0)
            iHour = 12;

        // Draw the hour hand.
        iAngle = (iHour * 30) % 360 + iMin / 2;
        fAngle = iAngle * 3.14159265358979323846 / 180.0;
        apt[0].x = xC;
        apt[0].y = yC;
        apt[1].x = xC + (int) (0.6 * iRadius * sin(fAngle));
        apt[1].y = yC - (int) (0.6 * iRadius * cos(fAngle));
        apt[2].x = xC - (int) (0.1 * iRadius * sin(fAngle));
        apt[2].y = yC + (int) (0.1 * iRadius * cos(fAngle));
        Polygon(hdc, apt, 3);

        // Draw the minute hand.
        iAngle = iMin * 6;
        fAngle = iAngle * 3.14159265358979323846 / 180.0;
        apt[0].x = xC;
        apt[0].y = yC;
        apt[1].x = xC + (int) (0.8 * iRadius * sin(fAngle));
        apt[1].y = yC - (int) (0.8 * iRadius * cos(fAngle));
        apt[2].x = xC - (int) (0.1 * iRadius * sin(fAngle));
        apt[2].y = yC + (int) (0.1 * iRadius * cos(fAngle));
        Polygon(hdc, apt, 3);

        // Draw the second hand.
        iAngle = iSec * 6;
        fAngle = iAngle * 3.14159265358979323846 / 180.0;
        MoveToEx(hdc, xC, yC, NULL);
        LineTo(hdc, xC + (int) (0.8 * iRadius * sin(fAngle)),
               yC - (int) (0.8 * iRadius * cos(fAngle)));

        // Draw the tick marks.
        for (i = 0; i < 60; i++)
        {
            if (i % 5 == 0)
            {
                MoveToEx(hdc,
                         xC + (int) ((iRadius - iMarker) * sin(i * 6 * 3.14159265358979323846 / 180.0)),
                         yC - (int) ((iRadius - iMarker) * cos(i * 6 * 3.14159265358979323846 / 180.0)),
                         NULL);
                LineTo(hdc,
                       xC + (int) (iRadius * sin(i * 6 * 3.14159265358979323846 / 180.0)),
                       yC - (int) (iRadius * cos(i * 6 * 3.14159265358979323846 / 180.0)));
            }
            else
            {
                MoveToEx(hdc,
                         xC + (int) ((iRadius - iMarker / 2) * sin(i * 6 * 3.14159265358979323846 / 180.0)),
                         yC - (int) ((iRadius - iMarker / 2) * cos(i * 6 * 3.14159265358979323846 / 180.0)),
                         NULL);
                LineTo(hdc,
                       xC + (int) (iRadius * sin(i * 6 * 3.14159265358979323846 / 180.0)),
                       yC - (int) (iRadius * cos(i * 6 * 3.14159265358979323846 / 180.0)));
            }
        }

        // Draw the center ellipse.
        Ellipse(hdc, xC - cxC, yC - cyC, xC + cxC, yC + cyC);

        // Draw the date and time.
        wsprintf(szBuffer, TEXT("%02d:%02d:%02d %s"), f24Hour ? iHour : iHour % 12, iMin, iSec, f24Hour ? TEXT("") : (iHour < 12 ? TEXT("AM") : TEXT("PM")));
        cx = GetSystemMetrics(SM_CXSCREEN);
        cy = GetSystemMetrics(SM_CYSCREEN);
        SetTextColor(hdc, RGB(255, 0, 0));
        SetBkMode(hdc, TRANSPARENT);
        TextOut(hdc, cx - 5 * cxBitmap / 4, cy - cyBitmap, szBuffer, lstrlen(szBuffer));

        // Clean up.
        DeleteDC(hdcMem);
        EndPaint(hwnd, &ps);
        return 0;

    case WM_DESTROY:
        KillTimer(hwnd, 1);
        DeleteObject(hBitmap);
        PostQuitMessage(0);
        return 0;

    case WM_KEYDOWN:
        switch (wParam)
        {
        case 'F':
        case 'f':
            f24Hour = !f24Hour;
            InvalidateRect(hwnd, NULL, TRUE);
            return 0;

        case VK_ESCAPE:
            DestroyWindow(hwnd);
            return 0;
        }
        break;
    }

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

程序中使用了双缓冲技术，可以避免闪烁问题。同时，程序还支持按下“F”键可以在12小时制和24小时制之间切换。