13.6.8  写串口函数的实现

写串口函数WriteChar()负责向串口输出数据，实现如下：

01  void CMySerial::WriteChar(CMySerial* port)  
02  {  
03      BOOL bWrite = TRUE;  
04      BOOL bResult = TRUE;  
05      DWORD BytesSent = 0;  
06      ResetEvent(port->m_hWriteEvent);  
07      //锁定临界资源  
08      EnterCriticalSection(&port->m_csCommunicationSync);   
09      if (bWrite)  
10      {  
11          port->m_ov.Offset = 0;  
12          port->m_ov.OffsetHigh = 0;  
13          //清空串口缓冲  
14          PurgeComm(port->m_hComm,   
15                      PURGE_RXCLEAR | PURGE_TXCLEAR | PURGE_RXABORT |   
16                      PURGE_TXABORT);       
17    
18          bResult = WriteFile(port->m_hComm, port->m_szWriteBuffer,   
19                          strlen((char*)port->m_szWriteBuffer),   
                            port->m_nWriteSize,   
20                          &BytesSent, &port->m_ov);   //向串口输出数据  
21          if (!bResult)    
22          {   //写串口失败  
23              DWORD dwError = GetLastError();  
24              switch (dwError)  
25              {  
26                  case ERROR_IO_PENDING:  
27                      {   //尚未写完数据  
28                          BytesSent = 0;  
29                          bWrite = FALSE;  
30                          break;  
31                      }  
32                  default:  
33                      {   //错误信息提示  
34                          port->ProcessErrorMessage("WriteFile()");  
35                      }  
36              }  
37          }   
38          else  
39          {   //解锁临界资源  
40              LeaveCriticalSection(&port->m_csCommunicationSync);  
41          }  
42      }  
43      if (!bWrite)  
44      {  
45          bWrite = TRUE;  
46          //等待写动作完成  
47          bResult = GetOverlappedResult(port->m_hComm, &port->m_ov,   
48                                      &BytesSent, TRUE);   
49          LeaveCriticalSection(&port->m_csCommunicationSync);  
50          if (!bResult)    
51          {  
52              port->ProcessErrorMessage("GetOverlappedResults() in                WriteFile()");  
53          }     
54      }   
55      //发送失败  
56      if (BytesSent != port->m_nWriteSize)  
57      {  
58          TRACE("WARNING: WriteFile() error.. Bytes Sent: %d; Message 59          Length: %d\n", BytesSent, strlen((char*)port->m_szWriteBuffer));  
60      }  
61  } 

【代码解析】

WriteChar()函数的处理过程和读串口函数的处理过程及其相似，可以参考读串口函数。