求助！！：：關于多執行緒實作一個稱重系統的代碼（純小白）-有解無憂

本人大一小白最近在自學用mfc的api函式寫一個串口通信。。主要是實作一個電子秤稱重系統，我用同步操作的方式做出來了（因為比較簡單），但是用異步做不出來，主要原因在于:要用到多執行緒的知識，但是在網上查了資料后還是看不懂概念。。
問題主要是執行緒函式怎么寫？？執行緒函式應該放在這個cpp的哪個位置？？以下的代碼是我讀寫串口的代碼（還沒加入執行緒的）
但是已經出現了一個問題：writefile函式的第四個引數回傳實際寫入的位元組數，但是我一直回傳的是0是怎么回事。。

BOOL write()

{

	char buffer[6]={0x55,0x11,0x00,0x00,0x11};

	COMSTAT ComStat;

	DWORD dwRetwrite=0;

	DWORD dwErrorFlags;

	OVERLAPPED m_osWrite;

	BOOL bWriteStat;

	memset(&m_osWrite,0,sizeof(m_osWrite));

	ClearCommError(hcom,&dwErrorFlags,&ComStat);

    PurgeComm(hcom, PURGE_TXABORT|PURGE_RXABORT|PURGE_TXCLEAR|PURGE_RXCLEAR);

	bWriteStat=WriteFile(hcom,buffer,5,&dwRetwrite,&m_osWrite);

	if(!bWriteStat)

	{

		if(GetLastError()==ERROR_IO_PENDING)

			WaitForSingleObject(m_osWrite.hEvent,INFINITE);

		else

			return FALSE;

	}

	return TRUE;

}

BOOL  read()

{

	char inBuffer[6]={0};

	

	DWORD dwRetread=0;

	

	OVERLAPPED m_osRead;

	memset(&m_osRead,0,sizeof(OVERLAPPED));

	m_osRead.hEvent=CreateEvent(NULL,TRUE,FALSE,NULL);

	BOOL bReadStatus;

	bReadStatus=ReadFile(hcom,inBuffer,5,&dwRetread,&m_osRead);

    if(!bReadStatus)

	{

		if(GetLastError()==ERROR_IO_PENDING)

		{

			WaitForSingleObject(m_osRead.hEvent,INFINITE);

		}

		return FALSE;

	}

	return TRUE;

}

uj5u.com熱心網友回復：

還有一個就是read函式中有個createevent的函式，這個是有什么意義？

uj5u.com熱心網友回復：

GetOverlappedResult 獲取掛起結果



  bWriteStat=WriteFile(hcom,buffer,5,&dwRetwrite,&m_osWrite);

  if(!bWriteStat && GetLastError()==ERROR_IO_PENDING)

  {

    bWriteStat = GetOverlappedResult(hcom, &m_osWrite, &dwRetwrite, TRUE)

  }

uj5u.com熱心網友回復：

Quote: 參考 2 樓 zgl7903 的回復:

GetOverlappedResult 獲取掛起結果
[code=c]
  bWriteStat=WriteFile(hcom,buffer,5,&dwRetwrite,&m_osWrite);
  if(!bWriteStat && GetLastError()==ERROR_IO_PENDING)
  {
    bWriteStat = GetOverlappedResult(hcom, &m_osWrite, &dwRetwrite, TRUE)
  }
不是很懂，WaiForSingleObject不是也可以嗎，這兩個函式有什么差別呢。
還有主要的是執行緒問題，我應該創建幾個執行緒，作用是用來干什么的呢？

uj5u.com熱心網友回復：

WaiForSingleObject 僅等待事件， GetOverlappedResult 還回傳寫入值個數

異步模式 OVERLAPPED 的 hEvent 要創建

Serial Communications in Win32



BOOL WriteABuffer(char * lpBuf, DWORD dwToWrite)

{

   OVERLAPPED osWrite = {0};

   DWORD dwWritten;

   DWORD dwRes;

   BOOL fRes;



   // Create this write operation's OVERLAPPED structure's hEvent.

   osWrite.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

   if (osWrite.hEvent == NULL)

      // error creating overlapped event handle

      return FALSE;



   // Issue write.

   if (!WriteFile(hComm, lpBuf, dwToWrite, &dwWritten, &osWrite)) {

      if (GetLastError() != ERROR_IO_PENDING) { 

         // WriteFile failed, but isn't delayed. Report error and abort.

         fRes = FALSE;

      }

      else

         // Write is pending.

         dwRes = WaitForSingleObject(osWrite.hEvent, INFINITE);

         switch(dwRes)

         {

            // OVERLAPPED structure's event has been signaled. 

            case WAIT_OBJECT_0:

                 if (!GetOverlappedResult(hComm, &osWrite, &dwWritten, FALSE))

                       fRes = FALSE;

                 else

                  // Write operation completed successfully.

                  fRes = TRUE;

                 break;

            

            default:

                 // An error has occurred in WaitForSingleObject.

                 // This usually indicates a problem with the

                // OVERLAPPED structure's event handle.

                 fRes = FALSE;

                 break;

         }

      }

   }

   else

      // WriteFile completed immediately.

      fRes = TRUE;



   CloseHandle(osWrite.hEvent);

   return fRes;

}

uj5u.com熱心網友回復：

參考 4 樓 zgl7903 的回復:

WaiForSingleObject 僅等待事件， GetOverlappedResult 還回傳寫入值個數

異步模式 OVERLAPPED 的 hEvent 要創建

Serial Communications in Win32



BOOL WriteABuffer(char * lpBuf, DWORD dwToWrite)

{

   OVERLAPPED osWrite = {0};

   DWORD dwWritten;

   DWORD dwRes;

   BOOL fRes;



   // Create this write operation's OVERLAPPED structure's hEvent.

   osWrite.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

   if (osWrite.hEvent == NULL)

      // error creating overlapped event handle

      return FALSE;



   // Issue write.

   if (!WriteFile(hComm, lpBuf, dwToWrite, &dwWritten, &osWrite)) {

      if (GetLastError() != ERROR_IO_PENDING) { 

         // WriteFile failed, but isn't delayed. Report error and abort.

         fRes = FALSE;

      }

      else

         // Write is pending.

         dwRes = WaitForSingleObject(osWrite.hEvent, INFINITE);

         switch(dwRes)

         {

            // OVERLAPPED structure's event has been signaled. 

            case WAIT_OBJECT_0:

                 if (!GetOverlappedResult(hComm, &osWrite, &dwWritten, FALSE))

                       fRes = FALSE;

                 else

                  // Write operation completed successfully.

                  fRes = TRUE;

                 break;

            

            default:

                 // An error has occurred in WaitForSingleObject.

                 // This usually indicates a problem with the

                // OVERLAPPED structure's event handle.

                 fRes = FALSE;

                 break;

         }

      }

   }

   else

      // WriteFile completed immediately.

      fRes = TRUE;



   CloseHandle(osWrite.hEvent);

   return fRes;

}

這里面的dwres和fres 的作用是什么？

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標籤：進程/線程/DLL

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