sy0902.htm

c语言经典教程

<p class=MsoNormal style='text-indent:20.9pt'><span class=GramE><span
lang=EN-US style='background:#D9D9D9'>const</span></span><span lang=EN-US
style='background:#D9D9D9'> OPEN_EXISTING = 3;</span></p>

<p class=MsoNormal style='margin-left:30.0pt;text-indent:-9.0pt'><span
style='font-size:9.0pt;font-family:宋体'>·</span><span lang=EN-US
style='font-size:9.0pt'>fdwAttrsAndFlags</span><span style='font-size:9.0pt;
font-family:宋体'>：描述了端口的各种属性。对于文件来说，有可能具有很多属性，但对于串口，唯一有意义的设置是</span><span
lang=EN-US style='font-size:9.0pt'>FILE_FLAG_OVERLAPPED</span><span
style='font-size:9.0pt;font-family:宋体'>。当创建时指定该设置，端口</span><span lang=EN-US
style='font-size:9.0pt'>I/O</span><span style='font-size:9.0pt;font-family:
宋体'>可以在后台进行（后台</span><span lang=EN-US style='font-size:9.0pt'>I/O</span><span
style='font-size:9.0pt;font-family:宋体'>也叫异步</span><span lang=EN-US
style='font-size:9.0pt'>I/O</span><span style='font-size:9.0pt;font-family:
宋体'>）。</span><span lang=EN-US style='font-size:9.0pt'>FILE_FLAG_OVERLAPPED</span><span
style='font-size:9.0pt;font-family:宋体'>常数定义如下：</span></p>

<p class=MsoNormal style='text-indent:20.9pt'><span class=GramE><span
lang=EN-US style='background:#D9D9D9'>const</span></span><span lang=EN-US
style='background:#D9D9D9'> FILE_FLAG_OVERLAPPED = 0x40000000h</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
style='font-family:宋体'>·</span><span lang=EN-US style='font-size:9.0pt'>hTemplateFile</span><span
style='font-size:9.0pt;font-family:宋体'>：指向模板文件的句柄，当端口处于打开状态时，不使用该参数，因而<span
class=GramE>必须置成</span></span><span lang=EN-US style='font-size:9.0pt'>0</span><span
style='font-size:9.0pt;font-family:宋体'>。</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
style='font-family:宋体'>调用</span><span lang=EN-US>CreateFile()</span><span
style='font-family:宋体'>函数打开</span><span lang=EN-US>COM1</span><span
style='font-family:宋体'>串口操作的例子如下所示：</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>HANDLE hCom;</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>DWORD dwError;</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>hCom=CreateFile(“COM1”, // </span><span
style='font-family:宋体;background:#D9D9D9'>文件名</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>GENERIC_READ | GENERIC_WRITE, // </span><span
style='font-family:宋体;background:#D9D9D9'>允许读和写</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>0, // </span><span style='font-family:
宋体;background:#D9D9D9'>独占方式</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>NULL,</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>OPEN_EXISTING, // </span><span
style='font-family:宋体;background:#D9D9D9'>打开而不是创建</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED,
// </span><span style='font-family:宋体;background:#D9D9D9'>重叠方式</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>NULL</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>);</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
class=GramE><span lang=EN-US style='background:#D9D9D9'>if(</span></span><span
lang=EN-US style='background:#D9D9D9'>hCom = = INVALID_HANDLE_VALUE)</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>{</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>dwError=GetLastError(); // </span><span
style='font-family:宋体;background:#D9D9D9'>处理错误</span></p>

<p class=MsoNormal style='margin-left:35.9pt;text-indent:-15.0pt'><span
lang=EN-US style='background:#D9D9D9'>}</span></p>

<p class=MsoNormal style='margin-left:.1pt;text-indent:20.9pt'><span
style='font-family:宋体'>一旦端口处于打开状态，就可以分配一个发送缓冲区和接收缓冲区，并且通过调用</span><span
lang=EN-US>SetupComm()</span><span style='font-family:宋体'>实现其它初始化工作。也可以不调用</span><span
lang=EN-US>SetupComm()</span><span style='font-family:宋体'>函数，</span><span
lang=EN-US>Windows</span><span style='font-family:宋体'>系统也会分配缺省的发送和接收缓冲区，并且初始化端口。但为了保证缓冲区的大小与实际需要的一致，最好还是调用该函数。</span><span
lang=EN-US>SetupComm()</span><span style='font-family:宋体'>函数声明如下：</span></p>

<p class=MsoNormal style='margin-left:.1pt;text-indent:20.9pt'><span
lang=EN-US style='background:#D9D9D9'>BOOL <span class=GramE>SetupComm(</span></span></p>

<p class=MsoNormal style='margin-left:.1pt;text-indent:26.15pt'><span
lang=EN-US style='background:#D9D9D9'>HANDLE hFile, // </span><span
style='font-family:宋体;background:#D9D9D9'>通信设备句柄</span></p>

<p class=MsoNormal style='margin-left:.1pt;text-indent:26.15pt'><span
lang=EN-US style='background:#D9D9D9'>DWORD dwInQueue, // </span><span
style='font-family:宋体;background:#D9D9D9'>输入缓冲区大小</span></p>

<p class=MsoNormal style='margin-left:.1pt;text-indent:26.15pt'><span
lang=EN-US style='background:#D9D9D9'>DWORD dwOutQueue // </span><span
style='font-family:宋体;background:#D9D9D9'>输出缓冲区大小</span></p>

<p class=MsoNormal style='margin-left:.1pt;text-indent:20.9pt'><span
lang=EN-US style='background:#D9D9D9'>);</span></p>

<p class=MsoNormal style='margin-left:.1pt;text-indent:20.9pt'><span
lang=EN-US>SetupComm()</span><span style='font-family:宋体'>函数中各项含义说明如下：</span></p>

<p class=MsoNormal style='margin-left:30.0pt;text-indent:-9.0pt'><span
style='font-size:9.0pt;font-family:宋体'>·</span><span lang=EN-US
style='font-size:9.0pt'>hFile: </span><span style='font-size:9.0pt;font-family:
宋体'>由</span><span lang=EN-US style='font-size:9.0pt'>GreatFile()</span><span
style='font-size:9.0pt;font-family:宋体'>返回的指向已打开端口的句柄。</span></p>

<p class=MsoNormal style='margin-left:30.0pt;text-indent:-9.0pt'><span
style='font-size:9.0pt;font-family:宋体'>·</span><span lang=EN-US
style='font-size:9.0pt'>dwInQueue</span><span style='font-size:9.0pt;
font-family:宋体'>和</span><span lang=EN-US style='font-size:9.0pt'>dwOutQueue: </span><span
style='font-size:9.0pt;font-family:宋体'>接收缓冲区的大小和发送缓冲区的大小。这两个定义并非是实际的缓冲区的大小，指定的大小仅仅是“推荐的”大小，而</span><span
lang=EN-US style='font-size:9.0pt'>Windows</span><span style='font-size:9.0pt;
font-family:宋体'>可以随意分配任意大小的缓冲区。</span><span lang=EN-US style='font-size:9.0pt'>Windows</span><span
style='font-size:9.0pt;font-family:宋体'>设备驱动程序可以获得这两个数据，并不直接分配大小，而使用来优化性能和避免缓冲区超限。</span></p>

<p class=MsoNormal style='margin-left:47.55pt;text-indent:-26.55pt'><span
style='font-size:9.0pt;font-family:宋体;background:#D9D9D9'>注意：当使用</span><span
lang=EN-US style='font-size:9.0pt;background:#D9D9D9'>CreateFile()</span><span
style='font-size:9.0pt;font-family:宋体;background:#D9D9D9'>函数打开串口时：为实现调制解调器的排他性访问，共享标识必须设为零；创建标识必须设为</span><span
lang=EN-US style='font-size:9.0pt;background:#D9D9D9'>OPEN_EXISTING</span><span
style='font-size:9.0pt;font-family:宋体;background:#D9D9D9'>；模板句柄<span
class=GramE>必须置为空</span>。</span></p>

<p class=MsoNormal style='margin-left:39.0pt;text-indent:-.25in'><span
lang=EN-US>2</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>．</span><span lang=EN-US
style='font-size:7.0pt'>&nbsp; </span><span style='font-family:宋体'>关闭串口</span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span style='font-family:宋体'>关闭串口比打开串口简单得多，只需要调用</span><span
lang=EN-US>CloseHandle()</span><span style='font-family:宋体'>函数关闭由</span><span
lang=EN-US>CreateHandle()</span><span style='font-family:宋体'>函数返回得<span
class=GramE>句柄即</span>可。</span></p>

<p class=MsoNormal style='margin-left:21.0pt'><span lang=EN-US>CloseHandle</span><span
style='font-family:宋体'>函数声明如下：</span></p>

<p class=MsoNormal style='margin-left:21.0pt'><span lang=EN-US
style='background:#D9D9D9'>BOOL <span class=GramE>CloseHandle(</span></span></p>

<p class=MsoNormal style='margin-left:21.0pt'><span lang=EN-US
style='background:#D9D9D9'>&nbsp; HANDLE hObject&nbsp;<span class=GramE>&nbsp;</span>
// </span><span style='font-family:宋体;background:#D9D9D9'>需关闭的设备句柄</span></p>

<p class=MsoNormal style='margin-left:21.0pt'><span lang=EN-US
style='background:#D9D9D9'>);</span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span style='font-family:宋体'>使用串口时一般要关闭它，如果忘记关闭串口，串口就会始终处于打开状态，其它应用程序就不能打开并使用串口了。</span></p>

<p class=MsoNormal><span lang=EN-US>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:.25in;text-indent:-.25in'><span
lang=EN-US>2.2</span><span lang=EN-US style='font-size:7.0pt'>&nbsp;<span
class=GramE>&nbsp;</span> </span><span style='font-family:宋体'>串口配置和串口属性</span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span lang=EN-US>Windows
9x/NT/2000</span><span style='font-family:宋体'>中配置串口提供了比</span><span lang=EN-US>Windows</span><span
style='font-family:宋体'>的早期版本更为强大的功能，当然相应也更加复杂。</span><span lang=EN-US>CreateFile</span><span
style='font-family:宋体'>函数打开串口后，系统将根据上次打开串口时设置的值来初始化串口，可以集成上次打开操作后的数值，包括设备控制块（</span><span
lang=EN-US>DCB</span><span style='font-family:宋体'>）和超时控制结构（</span><span
lang=EN-US>COMMTIMEOUTS</span><span style='font-family:宋体'>）。如果是首次打开串口，</span><span
lang=EN-US>Windows</span><span style='font-family:宋体'>操作系统就会使用缺省的配置。</span></p>

<p class=MsoNormal style='margin-left:39.0pt;text-indent:-.25in'><span
lang=EN-US>1</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";
mso-hansi-font-family:"Times New Roman"'>．</span><span lang=EN-US
style='font-size:7.0pt'>&nbsp; </span><span style='font-family:宋体'>串口配置</span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span lang=EN-US>Windows
9x/NT/2000</span><span style='font-family:宋体'>使用</span><span lang=EN-US>GetCommState()</span><span
style='font-family:宋体'>函数获取串口的当前配置，使用</span><span lang=EN-US>SetCommState()</span><span
style='font-family:宋体'>重新分配串口资源的各个参数。</span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span lang=EN-US>GetCommState()</span><span
style='font-family:宋体'>函数声明如下：</span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span lang=EN-US
style='background:#D9D9D9'>BOOL <span class=GramE>GetCommState(</span></span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span lang=EN-US
style='background:#D9D9D9'>&nbsp;&nbsp; HANDLE hFile, // </span><span
style='font-family:宋体;background:#D9D9D9'>通信设备句柄</span></p>