用vc画图当把图复制到剪贴板时并通过GetTextExtent得到字符长度

以下是用VC画图并获取字符长度的示例代码：

#include <windows.h>
#include <tchar.h>

LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX wc = {0};
    wc.cbSize = sizeof(wc);
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = WndProc;
    wc.hInstance = hInstance;
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wc.lpszClassName = _T("MyWindowClass");
    RegisterClassEx(&wc);

    HWND hWnd = CreateWindowEx(0, _T("MyWindowClass"), _T("My Window"), WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, hInstance, NULL);

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

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

    return (int)msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    static HBITMAP hBitmap = NULL;
    static int cx, cy;
    static TCHAR szText[] = _T("Hello, World!");
    static int nTextLength = _tcslen(szText);
    static SIZE szTextSize;

    switch (msg)
    {
    case WM_CREATE:
        {
            HDC hDC = GetDC(hWnd);
            hBitmap = CreateCompatibleBitmap(hDC, 400, 300);
            ReleaseDC(hWnd, hDC);
            cx = 400;
            cy = 300;
        }
        break;

    case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hDC = BeginPaint(hWnd, &ps);

            HDC hMemDC = CreateCompatibleDC(hDC);
            HBITMAP hOldBitmap = (HBITMAP)SelectObject(hMemDC, hBitmap);

            RECT rc = {0, 0, cx, cy};
            FillRect(hMemDC, &rc, (HBRUSH)(COLOR_WINDOW + 1));

            HFONT hFont = CreateFont(24, 0, 0, 0, FW_BOLD, FALSE, FALSE, FALSE, DEFAULT_CHARSET,
                OUT_DEFAULT_PRECIS, CLIP_DEFAULT_PRECIS, DEFAULT_QUALITY, DEFAULT_PITCH | FF_DONTCARE, _T("Arial"));
            HFONT hOldFont = (HFONT)SelectObject(hMemDC, hFont);

            SetTextColor(hMemDC, RGB(255, 0, 0));
            SetBkMode(hMemDC, TRANSPARENT);
            TextOut(hMemDC, 100, 100, szText, nTextLength);

            SelectObject(hMemDC, hOldFont);
            DeleteObject(hFont);

            SelectObject(hMemDC, hOldBitmap);
            DeleteDC(hMemDC);

            BitBlt(hDC, 0, 0, cx, cy, hMemDC, 0, 0, SRCCOPY);

            EndPaint(hWnd, &ps);
        }
        break;

    case WM_DESTROY:
        DeleteObject(hBitmap);
        PostQuitMessage(0);
        break;

    case WM_COPY:
        {
            if (OpenClipboard(hWnd))
            {
                EmptyClipboard();

                HDC hMemDC = CreateCompatibleDC(NULL);
                HBITMAP hOldBitmap = (HBITMAP)SelectObject(hMemDC, hBitmap);

                BITMAPINFOHEADER bih = {0};
                bih.biSize = sizeof(bih);
                bih.biWidth = cx;
                bih.biHeight = cy;
                bih.biPlanes = 1;
                bih.biBitCount = 24;
                bih.biCompression = BI_RGB;
                bih.biSizeImage = cx * cy * 3;

                HGLOBAL hDIB = GlobalAlloc(GHND, sizeof(bih) + bih.biSizeImage);
                LPBYTE pDIB = (LPBYTE)GlobalLock(hDIB);
                memcpy(pDIB, &bih, sizeof(bih));
                LPBYTE pBits = pDIB + sizeof(bih);
                GetDIBits(hMemDC, hBitmap, 0, cy, pBits, (BITMAPINFO*)&bih, DIB_RGB_COLORS);

                GlobalUnlock(hDIB);
                SetClipboardData(CF_DIB, hDIB);

                SelectObject(hMemDC, hOldBitmap);
                DeleteDC(hMemDC);

                CloseClipboard();
            }

            // Get text length
            HDC hDC = GetDC(hWnd);
            HFONT hFont = CreateFont(24, 0, 0, 0, FW_BOLD, FALSE, FALSE, FALSE, DEFAULT_CHARSET,
                OUT_DEFAULT_PRECIS, CLIP_DEFAULT_PRECIS, DEFAULT_QUALITY, DEFAULT_PITCH | FF_DONTCARE, _T("Arial"));
            HFONT hOldFont = (HFONT)SelectObject(hDC, hFont);

            GetTextExtentPoint32(hDC, szText, nTextLength, &szTextSize);

            SelectObject(hDC, hOldFont);
            DeleteObject(hFont);

            ReleaseDC(hWnd, hDC);
        }
        break;

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

    return 0;
}

在窗口中绘制一段文本，并在复制到剪贴板时获取文本长度。在 WM_COPY 消息中，我们首先创建一个兼容的内存 DC，将位图选入 DC，并将位图复制到内存 DC 中。然后，我们创建一个 DIB 并将其锁定以获取指向位图数据的指针。接下来，我们将位图数据复制到 DIB 中，并将 DIB 放入剪贴板中。最后，我们使用 GetTextExtentPoint32 函数获取文本大小，并将其存储在 szTextSize 变量中