这段代码中哪个 ReadFile 参数不正确？（错误代码 87）

Question

(编辑： 除了 headers 和 main() 函数的括号外，我没有排除任何代码。此处列出的代码行之间没有任何内容。 )

.

我使用 ReadFile 函数读取此 COM3 端口（未返回 INVALID_HANDLE_VALUE 或 ERROR_FILE_NOT_FOUND）：

LPCTSTR portName = "COM3" ;

HANDLE hSerial;
hSerial = CreateFile(portName,
                     GENERIC_READ | GENERIC_WRITE,
                     0,    // exclusive access
                     NULL, // default security attributes
                     OPEN_EXISTING,
                     FILE_FLAG_OVERLAPPED,
                     NULL);

有问题的 ReadFile 函数使用以下参数：

DWORD n = 512 ;
char szBuff[n] = {0};
DWORD dwBytesRead = 0;

if(!ReadFile(hSerial, szBuff, n, &dwBytesRead, NULL))
{
    cout << "ReadFile error. Error code: " << GetLastError() << endl ;
    cin.get() ;
    return 0 ;
}

我应该引入哪些更改才能使读取成功？

（我搜索了该函数的文档和其他 Whosebug 问题，测试了很多东西，但找不到答案。）

Answer 1

Marcin Jędrzejewski 关于重叠 IO 标志与 ReadFile 函数之间不匹配的回答是正确的，但我将保留它只是为了提供帮助。
您缺少很多初始化，这可能对您操作 COM 端口有帮助。

此代码用于使用 C++ 打开、配置和读取 windows 上的 COM 端口。

供参考

READ_BUFFER_SIZE = 1024;
WRITE_BUFFER_SIZE = 1024;
COM_READ_BUFFER_SIZE = 1024;
COM_WRITE_BUFFER_SIZE = 1024;
READ_TIMEOUT = 50;
WRITE_TIMEOUT = 100;

port = "\.\COM6"
portFormat = "9600,N,8,1" /* for information on this, google the MODE command for windows. */

HANDLE hComPort;
DCB dcbComConfig;

正在打开 COM 端口

DWORD dwStoredFlags = EV_BREAK | EV_ERR | EV_RXCHAR;
COMMTIMEOUTS timeouts;

FillMemory(&dcbComConfig, sizeof(dcbComConfig), 0);
dcbComConfig.DCBlength = sizeof(dcbComConfig);

/* assign a COM format to the COM Port. */
if(!BuildCommDCB(portFormat, &dcbComConfig))
{
    printf("Failed to build comm format data %s\n", portFormat);
}

/* Open the COM port with overlapped IO. */
hComPort = CreateFile(port, GENERIC_READ | GENERIC_WRITE, 0, 0, 
                OPEN_EXISTING, FILE_FLAG_OVERLAPPED, 0);

if (hComPort == INVALID_HANDLE_VALUE)
{
    printf("Error opening port %s\n", port);
}

/* Set the COM Ports internal Read and Write buffer sizes. */
if(!SetupComm(hComPort, COM_READ_BUFFER_SIZE, COM_WRITE_BUFFER_SIZE))
{
    printf("Could not set COM buffers\n");
}

/* assign the previously created COM Format to the COM Port. */
if(!SetCommState(hComPort, &dcbComConfig))
{
    printf("Error setting com to format data.\n");
}

/* Mask what events you want to look for in the COM Port. */
if (!SetCommMask(hComPort, dwStoredFlags))
{
    printf("Error setting communications mask\n");
}

/*-- Read Timeouts set like this so we can use the event based reading. --*/
timeouts.ReadIntervalTimeout = MAXDWORD; 
timeouts.ReadTotalTimeoutMultiplier = 0;
timeouts.ReadTotalTimeoutConstant = 0;
timeouts.WriteTotalTimeoutMultiplier = 10;
timeouts.WriteTotalTimeoutConstant = 100;

if (!SetCommTimeouts(hComPort, &timeouts))
{
    printf("Error setting time-outs.\n");
}

正在读取 COM 端口

DWORD dwRead = 0;
DWORD dwComEvent = EV_RXCHAR;
DWORD lpErrors = 0;
char readBuffer[READ_BUFFER_SIZE];

/* Create the Overlapped IO Read Event. */
OVERLAPPED osRead = {0};
osRead.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

/* Used to monitor the COM Port State. */
COMSTAT ComStatus;

/* Loop at 20Hz to read the COM Port until a Kill event has been set. */
while(WaitForSingleObject(hKillEvent, 50) == WAIT_TIMEOUT)
{
    /* Wait for a COM Event to occur ( Read Event in this Case ). */
    if (WaitCommEvent(hComPort, &dwComEvent , NULL))
    {
        /* If the COM Port had an error Clear it. */
        ClearCommError(hComPort, &lpErrors, &ComStatus);
        /*-- Reset read operation's OVERLAPPED structure's hEvent --*/
        ResetEvent(osRead.hEvent);

        if (ReadFile(hComPort, readBuffer, ComStatus.cbInQue, &dwRead, &osRead))
        {
            /*-- bytes have been read; process it --*/
            USE_DATA(readBuffer, dwRead);
        }
        else
        {
            /*-- An error occurred in the ReadFile call --*/
            printf("ReadFile encountered an error.\n");
            break;
        }
    }
    else 
    {
        /*-- Error in WaitCommEvent --*/
        printf("WaitCommEvent encountered an error.\n");
        break;
    }
}

/* Close the Overlapped IO Read Event. */
CloseHandle(osRead.hEvent);

Answer 2

在 ReadFile 文档中，您可以阅读：

lpOverlapped [in, out, optional] A pointer to an OVERLAPPED structure is required if the hFile parameter was opened with FILE_FLAG_OVERLAPPED, otherwise it can be NULL.

因此，由于您在 CreateFile 中指定了 FILE_FLAG_OVERLAPPED，因此您应该在 ReadFile 中提供 OVERLAPPED。

在 CreateFile 中，您可以阅读 Communications Resources 的参数：

... and the handle can be opened for overlapped I/O.

因此您可以在 CreateFile

中跳过 FILE_FLAG_OVERLAPPED

Answer 3

最上面的答案是正确的。在这种情况下，以 FILE_FLAG_OVERLAPPED 开头，ReadFile 需要一个 OVERLAPPED 结构作为最后一个参数。

想补充一点，如果您确实提供了 OVERLAPPED 结构，但忘记 ZeroMemory 它，您也可能会遇到 'parameter is incorrect' 错误。

来自documentation：

Any unused members of this structure should always be initialized to zero before the structure is used in a function call. Otherwise, the function may fail and return ERROR_INVALID_PARAMETER.

所以不要忘记：

OVERLAPPED ovl;
ZeroMemory(&ovl, sizeof(ovl));
...
ReadFile(hSerial, szBuff, n, &dwBytesRead, &ovl);

这段代码中哪个 ReadFile 参数不正确？（错误代码 87）

Which ReadFile parameter in this code is incorrect? (Error code 87)

c++

port

readfile

供参考

正在打开 COM 端口

正在读取 COM 端口

这段代码中哪个 ReadFile 参数不正确？ （错误代码 87）

Which ReadFile parameter in this code is incorrect? (Error code 87)

c++

port

readfile

供参考

正在打开 COM 端口

正在读取 COM 端口

这段代码中哪个 ReadFile 参数不正确？（错误代码 87）