自学教程：C++ CanSeek函数代码示例

void Buffer::SetPos(int value) {    if ((value >= fileLen) && (stream != NULL) && !CanSeek()) {        // Wanted position is after buffer and the stream        // is not seek-able e.g. network or console,        // thus we have to read the stream manually till        // the wanted position is in sight.        while ((value >= fileLen) && (ReadNextStreamChunk() > 0));    }    if ((value < 0) || (value > fileLen)) {        wprintf(L"--- buffer out of bounds access, position: %d/n", value);        MX_DEBUG_BREAK;        exit(1);    }    if ((value >= bufStart) && (value < (bufStart + bufLen))) { // already in buffer        bufPos = value - bufStart;    } else if (stream != NULL) { // must be swapped in        fseek(stream, value, SEEK_SET);        bufLen = fread(buf, sizeof(unsigned char), bufCapacity, stream);        bufStart = value;        bufPos = 0;    } else {        bufPos = fileLen - bufStart; // make Pos return fileLen    }}

void MediaPlayer2Player::currentSourceChanged() const{    QVariantMap properties;    properties["Metadata"] = Metadata();    properties["CanSeek"] = CanSeek();    Mpris2::signalPropertiesChange(this, properties);}

void PAPlayer::Seek(bool bPlus, bool bLargeStep, bool bChapterOverride){  if (!CanSeek()) return;  __int64 seek;  if (g_advancedSettings.m_musicUseTimeSeeking && GetTotalTime() > 2 * g_advancedSettings.m_musicTimeSeekForwardBig)  {    if (bLargeStep)      seek = bPlus ? g_advancedSettings.m_musicTimeSeekForwardBig : g_advancedSettings.m_musicTimeSeekBackwardBig;    else      seek = bPlus ? g_advancedSettings.m_musicTimeSeekForward : g_advancedSettings.m_musicTimeSeekBackward;    seek *= 1000;    seek += GetTime();  }  else  {    float percent;    if (bLargeStep)      percent = bPlus ? (float)g_advancedSettings.m_musicPercentSeekForwardBig : (float)g_advancedSettings.m_musicPercentSeekBackwardBig;    else      percent = bPlus ? (float)g_advancedSettings.m_musicPercentSeekForward : (float)g_advancedSettings.m_musicPercentSeekBackward;    seek = (__int64)(GetTotalTime64() * (GetPercentage() + percent) / 100);  }  SeekTime(seek);}

void Mpris::updateStatus(){    QVariantMap map;    if (MPDStatus::self()->repeat()!=status.repeat) {        map.insert("LoopStatus", LoopStatus());    }    if (MPDStatus::self()->random()!=status.random) {        map.insert("Shuffle", Shuffle());    }    if (MPDStatus::self()->volume()!=status.volume) {        map.insert("Volume", Volume());    }    if (MPDStatus::self()->playlistLength()!=status.playlistLength) {        map.insert("CanGoNext", CanGoNext());        map.insert("CanGoPrevious", CanGoPrevious());    }    if (MPDStatus::self()->state()!=status.state) {        map.insert("PlaybackStatus", PlaybackStatus());        map.insert("CanPlay", CanPlay());        map.insert("CanPause", CanPause());        map.insert("CanSeek", CanSeek());    }    if (MPDStatus::self()->timeElapsed()!=status.timeElapsed) {        map.insert("Position", convertTime(MPDStatus::self()->timeElapsed()));    }    if (!map.isEmpty() || MPDStatus::self()->songId()!=status.songId) {        if (!map.contains("Position")) {            map.insert("Position", convertTime(MPDStatus::self()->timeElapsed()));        }        map.insert("Metadata", Metadata());        signalUpdate(map);    }    status=MPDStatus::self()->getValues();}

void MediaPlayer2Player::currentSourceChanged() const{    QVariantMap properties;    properties["Metadata"] = Metadata();    properties["CanSeek"] = CanSeek();    properties["PlaybackStatus"] = PlaybackStatus();    signalPropertiesChange(properties);}

void PAPlayer::SeekTime(__int64 iTime /*=0*/){  if (!CanSeek()) return;  if (m_currentFile->m_lStartOffset)    iTime += m_currentFile->m_lStartOffset * 1000 / 75;  m_SeekTime = iTime;  CLog::Log(LOGDEBUG, "PAPlayer::Seeking to time %f", 0.001f * m_SeekTime);}

void PAPlayer::SeekTime(__int64 iTime /*=0*/){  if (!CanSeek()) return;  int seekOffset = (int)(iTime - GetTime());  if (m_currentFile->m_lStartOffset)    iTime += m_currentFile->m_lStartOffset * 1000 / 75;  m_SeekTime = iTime;  m_callback.OnPlayBackSeek((int)m_SeekTime, seekOffset);  CLog::Log(LOGDEBUG, "PAPlayer::Seeking to time %f", 0.001f * m_SeekTime);}

int Buffer::Read() {	if (bufPos < bufLen) {		return buf[bufPos++];	} else if (GetPos() < fileLen) {		SetPos(GetPos()); // shift buffer start to Pos		return buf[bufPos++];	} else if ((stream != NULL) && !CanSeek() && (ReadNextStreamChunk() > 0)) {		return buf[bufPos++];	} else {		return EoF;	}}

Buffer::Buffer(FILE* s, bool isUserStream) {// ensure binary read on windows#if _MSC_VER >= 1300	_setmode(_fileno(s), _O_BINARY);#endif	stream = s; this->isUserStream = isUserStream;	if (CanSeek()) {		fseek(s, 0, SEEK_END);		fileLen = ftell(s);		fseek(s, 0, SEEK_SET);		bufLen = (fileLen < MAX_BUFFER_LENGTH) ? fileLen : MAX_BUFFER_LENGTH;		bufStart = INT_MAX; // nothing in the buffer so far	} else {		fileLen = bufLen = bufStart = 0;	}	bufCapacity = (bufLen>0) ? bufLen : MIN_BUFFER_LENGTH;	buf = new unsigned char[bufCapacity];		if (fileLen > 0) SetPos(0);          // setup  buffer to position 0 (start)	else bufPos = 0; // index 0 is already after the file, thus Pos = 0 is invalid	if (bufLen == fileLen && CanSeek()) Close();}

int64_t CInputStreamPVRBase::Seek(int64_t offset, int whence){  if (whence == SEEK_POSSIBLE)    return CanSeek() ? 1 : 0;  int64_t ret = SeekPVRStream(offset, whence);  // if we succeed, we are not eof anymore  if (ret >= 0)    m_eof = false;  return ret;}

void PAPlayer::SeekTime(int64_t iTime /*=0*/){  if (!CanSeek()) return;  CSharedLock lock(m_streamsLock);  if (!m_currentStream)    return;  int seekOffset = (int)(iTime - GetTimeInternal());  if (m_playbackSpeed != 1)    ToFFRW(1);  m_currentStream->m_seekFrame = (int)((float)m_currentStream->m_sampleRate * ((float)iTime + (float)m_currentStream->m_startOffset) / 1000.0f);  m_callback.OnPlayBackSeek((int)iTime, seekOffset);}

void CApplicationPlayer::SetPlaySpeed(int iSpeed, bool bApplicationMuted){  boost::shared_ptr<IPlayer> player = GetInternal();  if (!player)    return;  if (!IsPlayingAudio() && !IsPlayingVideo())    return ;  if (m_iPlaySpeed == iSpeed)    return ;  if (!CanSeek())    return;  if (IsPaused())  {    if (      ((m_iPlaySpeed > 1) && (iSpeed > m_iPlaySpeed)) ||      ((m_iPlaySpeed < -1) && (iSpeed < m_iPlaySpeed))    )    {      iSpeed = m_iPlaySpeed; // from pause to ff/rw, do previous ff/rw speed    }    Pause();  }  m_iPlaySpeed = iSpeed;  ToFFRW(m_iPlaySpeed);  // if player has volume control, set it.  if (ControlsVolume())  {    if (m_iPlaySpeed == 1)    { // restore volume      player->SetVolume(g_application.GetVolume(false));    }    else    { // mute volume      player->SetVolume(VOLUME_MINIMUM);    }    player->SetMute(bApplicationMuted);  }}

size_t FileStream::Seek(StreamSeek seek, int pos){    if (!CanSeek())    {        return 0;    }    int stdclib_seek;    switch (seek)    {    case kSeekBegin:    stdclib_seek = SEEK_SET; break;    case kSeekCurrent:  stdclib_seek = SEEK_CUR; break;    case kSeekEnd:      stdclib_seek = SEEK_END; break;    default:        // TODO: warning to the log        return 0;    }    fseek(_file, pos, stdclib_seek);    return GetPosition();}

void Mpris2::slotCurrentSourceChanged(){    EmitPropertyChanged("Metadata", Metadata());    EmitPropertyChanged("CanSeek", CanSeek());}