CreateFile() 串行通信问题

Question

我正在尝试通过我的 USB 端口（名为 COM15）进行一些串行通信，但出现错误。这是发生错误的代码：

HANDLE myPortHandle = CreateFile("COM15",
                                  GENERIC_READ | GENERIC_WRITE,
                                  0,
                                  NULL,
                                  OPEN_EXISTING,
                                  0,
                                  NULL);

if (myPortHandle == INVALID_HANDLE_VALUE)
{
    DWORD lastError = GetLastError();
    cout<<"ERROR HERE! = "<<lastError<<endl;
}

我每次编译程序，打开串口的句柄==INVALID_HANDLE_VALUE。我在 CreateFile() msdn 文档中读到要使用 GetLastError() 以获得 "extended error information"。现在...当我运行代码时，GetLastError() returns 的值为：2

在 GetLastError() 的 msdn 文档中，它说：

"The Return Value section of the documentation for each function that sets the last-error code notes the conditions under which the function sets the last-error code."

我尝试在 CreateFile() msdn 文档的 Return 值部分查找“2”的含义，但在任何地方都找不到其含义。

问题：

1) 为什么会这样：myPortHandle == INVALID_HANDLE_VALUE？

2) 此外，如果有人能指导我到 msdn 文档中查找 GetLastError() 返回的“2”的含义，那就太棒了！

Answer 1

Windows 错误代码记录在此处：http://msdn.microsoft.com/en-us/library/windows/desktop/ms681382.aspx

您的错误代码是 ERROR_FILE_NOT_FOUND。这意味着无法找到 COM15。根据 this article 您需要使用名称："\\.\COM15".

CreateFile() can be used to get a handle to a serial port. The "Win32 Programmer's Reference" entry for "CreateFile()" mentions that the share mode must be 0, the create parameter must be OPEN_EXISTING, and the template must be NULL.

CreateFile() is successful when you use "COM1" through "COM9" for the name of the file; however, the message INVALID_HANDLE_VALUE is returned if you use "COM10" or greater.

If the name of the port is \.\COM10, the correct way to specify the serial port in a call to CreateFile() is as follows:
CreateFile(
  "\\.\COM10",     // address of name of the communications device
  fdwAccess,          // access (read-write) mode
  0,                  // share mode
  NULL,               // address of security descriptor
  OPEN_EXISTING,      // how to create
  0,                  // file attributes
  NULL                // handle of file with attributes to copy
);
NOTES: This syntax also works for ports COM1 through COM9. Certain boards will let you choose the port names yourself. This syntax works for those names as well.

或者从文档到 CreateFile 本身：

The CreateFile function can create a handle to a communications resource, such as the serial port COM1. For communications resources, the dwCreationDisposition parameter must be OPEN_EXISTING, the dwShareMode parameter must be zero (exclusive access), and the hTemplateFile parameter must be NULL. Read, write, or read/write access can be specified, and the handle can be opened for overlapped I/O.

To specify a COM port number greater than 9, use the following syntax: \.\COM10. This syntax works for all port numbers and hardware that allows COM port numbers to be specified.

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