WinAPI: midiOutUnprepareHeader - 清除由 midiOutPrepareHeader 完成的准备

提示:
设备写满缓冲区返回给程序后, 须调用此函数;
释放(GlobalFree)缓冲区前, 须调用此函数;
取消一个尚未准备的缓冲区将无效, 但函数返回 0

---

//声明:

midiOutUnprepareHeader(

  hMidiOut: HMIDIOUT;     {设备句柄}

  lpMidiOutHdr: PMidiHdr; {TMidiHdr 结构指针}

  uSize: UINT             {TMidiHdr 结构大小}

): MMRESULT;             {成功返回 0; 可能的错误值如下:}



MMSYSERR_INVALHANDLE = 5;  {设备句柄无效}

MIDIERR_STILLPLAYING = 65; {缓冲区还在队列中}



//TMidiHdr 是 midihdr_tag 结构的重定义:

midihdr_tag = record

  lpData: PChar;               {专用缓冲区的指针}

  dwBufferLength: DWORD;       {指定缓冲区长度}

  dwBytesRecorded: DWORD;      {输入时, 指定缓冲区中的数据量}

  dwUser: DWORD;               {指定用户数据}

  dwFlags: DWORD;              {指定缓冲区信息标志}

  lpNext: PMidiHdr;            {保留(给设备)}

  reserved: DWORD;             {保留(给设备)}

  dwOffset: DWORD;             {回调开始时, 缓冲区的偏移}

  dwReserved: array[0..7] of DWORD; {保留(给系统)}

end;



//dwFlags 的可选值:

MHDR_DONE     = $00000001; {设备已把缓冲区交还给程序}

MHDR_PREPARED = $00000002; {已为 midiInPrepareHeader 或 midiOutPrepareHeader 准备好缓冲区}

MHDR_INQUEUE  = $00000004; {保留(给设备)}

MHDR_ISSTRM   = $00000008; {是流缓冲区}


 
   




//举例: