如何获取messagebox中显示的内容？用sdk

BOOL CALLBACK EnumWindowsProc(HWND hwnd, LPARAM lParam)
{
    TCHAR szBuf[4096];
    GetClassName(hwnd, szBuf, sizeof(szBuf));
    string str = szBuf;
    if(!("#32770"))
    {
        HWND hSubWnd = GetDlgItem(hwnd, 0xffff);
        if(hSubWnd)
        {
            int len = GetWindowText(hSubWnd, szBuf, sizeof(szBuf));
            cout << "Found it:" <<szBuf <<endl;
        }
    }
    return TRUE;
}