我尝试在C中编写一个基于事件的小型应用程序来进行串口读取（下面的源代码）。我的程序是使用WinApi函数。 comport.c具有为处理COM端口（open，read，write）而编写的函数，utils.c具有一些辅助函数。
我的程序始终产生以下输出：
选择COM1进行收听。
GetCommMask结果：0x00000029（EV_RXCHAR：0x0001，EV_CTS：0x0008，EV_RLSD：0x0020）
按任意键继续......
I / O正在等待（WaitCommEvent）......
I / O正在等待（WaitCommEvent）......
I / O正在等待（WaitCommEvent）......
I / O正在等待（WaitCommEvent）......
I / O正在等待（WaitCommEvent）......
似乎WaitCommEvent函数失败，GetLastError（）返回错误87（I / O挂起）。
请帮我找出问题所在，哪个参数无效？见下面的代码。
main.c：
#include "stdafx.h"
#include "comport.h"
#include "utils.h"
#include <conio.h>
#define READ_BUFF_MAX_LENGTH 1024
int _tmain(int argc, _TCHAR* argv[])
{
DWORD dwEvtMask;
HANDLE hComPort;
OVERLAPPED oEventHandler;
int portNum;
DWORD readTotal;
BOOL bOverlappedPending = FALSE;
char readBuff[READ_BUFF_MAX_LENGTH];
if(2 > argc)
{
printf("Use the program: ZliFuerZlvbusInterface.exe XXX (where XXX is the number of com port), \r\ne.G. for COM1 -> ZliFuerZlvbusInterface.exe 1\r\n");
return 1;
}
else
{
portNum = atoi(argv[1]);
if(0 == IsValidComNumber(portNum))
{
printf("ERROR: COM port number %d is invalid (parsed from '%s').\r\n", portNum, argv[1]);
return 2;
}
else
{
printf("COM%d is selected to be listened.\r\n", portNum);
}
}
if(0 == CreateSerialConnection(&hComPort, &oEventHandler, portNum, 1200, 8, EVEN, STOP1))
{
return 3;
}
if(FALSE == GetCommMask(hComPort, &dwEvtMask))
{
printf("GetCommMask failed with error:\r\n");
PrintLastErrorText();
return 4;
}
else
{
printf("GetCommMask result: 0x%08X (EV_RXCHAR: 0x0001, EV_CTS: 0x0008, EV_RLSD: 0x0020)\r\n", dwEvtMask);
}
printf("Press any key to proceed...\r\n");
getch();
while(1)
{
if(0 != kbhit())
{
if(27 == getch()) // ESC pressed
{
printf("Key ESC pressed, exiting...\r\n");
break;
}
}
bOverlappedPending = FALSE;
readTotal = 0;
if(TRUE == WaitCommEvent(hComPort, &dwEvtMask, &oEventHandler))
{
if(dwEvtMask & EV_CTS) // Clear-to-send signal present
{
PrintCurrentDateTime();
printf("COM%d: Clear-to-send signal set\r\n", portNum);
}
if(dwEvtMask & EV_RLSD) // Data-carrier-detect signal present
{
PrintCurrentDateTime();
printf("COM%d: Data-carrier-detect signal set\r\n", portNum);
}
if(dwEvtMask & EV_RXCHAR) // Data received
{
ReadSerial(&hComPort, &oEventHandler, portNum, readBuff, READ_BUFF_MAX_LENGTH);
}
}
else
{
if(ERROR_IO_PENDING == GetLastError())
{
printf("I/O is pending (WaitCommEvent)...\r\n");
bOverlappedPending = TRUE;
}
else
{
printf("WaitCommEvent failed with error:\r\n");
PrintLastErrorText();
}
}
if(TRUE == bOverlappedPending)
{
if(FALSE == GetOverlappedResult(hComPort, &oEventHandler, &readTotal, TRUE))
{
printf("GetOverlappedResult failed with error:\r\n");
PrintLastErrorText();
}
}
}
CloseSerialConnection(&hComPort);
return 0;
}
comport.c：
#include <stdio.h>
#include "comport.h"
#include "utils.h"
int IsValidComNumber(int com)
{
if ((com < 1) ||
(com > 256))
{
return 0;
}
return 1;
}
int IsValidBaud(int baud)
{
switch(baud)
{
case CBR_110:
case CBR_300:
case CBR_600:
case CBR_1200:
case CBR_2400:
case CBR_4800:
case CBR_9600:
case CBR_14400:
case CBR_19200:
case CBR_38400:
case CBR_56000:
case CBR_57600:
case CBR_115200:
case CBR_128000:
case CBR_256000:
{
return 1;
break;
}
default:
{
break;
}
}
return 0;
}
int IsValidBits(int bits)
{
if ((bits < 5) ||
(bits > 8))
{
return 0;
}
else
{
return 1;
}
}
int CreateSerialConnection(HANDLE* handle, OVERLAPPED* overlapped, int portNumber, int baud, int bits, enum ParType parity, enum StopType stopbits)
{
DCB dcb;
COMMTIMEOUTS timeouts;
TCHAR portVirtualFile[32];
// For serial port name this format must be used (as virtual file): "\\\\.\\COMx"
memset(portVirtualFile, 0, 32);
#ifdef _UNICODE
swprintf(portVirtualFile, 32, L"\\\\.\\COM%d", portNumber);
#else
sprintf_s(portVirtualFile, 32, "\\\\.\\COM%d", portNumber);
#endif
if(0 == IsValidBaud(baud))
{
printf("ERROR: Specified baud rate %d is invalid for serial connection to COM%d.\r\n", baud, portNumber);
return 0;
}
if(0 == IsValidBits(bits))
{
printf("ERROR: Specified number of data bits %d is invalid for serial connection to COM%d.\r\n", bits, portNumber);
return 0;
}
*handle = CreateFile(portVirtualFile, // Specify port device
GENERIC_READ | GENERIC_WRITE, // Specify mode that open device.
0, // the devide isn't shared.
NULL, // the object gets a default security.
OPEN_EXISTING, // Specify which action to take on file.
FILE_FLAG_OVERLAPPED, // Use overlapped I/O.
NULL); // default.
if(*handle == INVALID_HANDLE_VALUE)
{
printf("ERROR: Opening serial port COM%d failed\r\n", portNumber);
return 0;
}
if(FALSE == GetCommState(*handle, &dcb))
{
printf("ERROR: Getting current state of COM%d\r\n", portNumber);
PrintLastErrorText();
return 0;
}
memset(&dcb, 0, sizeof(dcb)); //zero initialize the structure
dcb.DCBlength = sizeof(dcb); //fill in length
dcb.BaudRate = baud; // baud rate
dcb.ByteSize = bits; // data size, xmit and rcv
dcb.Parity = parity; // parity bit
dcb.StopBits = stopbits; // stop bits
if(FALSE == SetCommState(*handle, &dcb))
{
printf("ERROR: Setting new state of COM%d failed.\r\n", portNumber);
PrintLastErrorText();
return 0;
}
if(FALSE == SetCommMask(*handle, EV_RXCHAR | EV_CTS | EV_RLSD))
{
printf("ERROR: Setting new COM MASK (events) for COM%d failed.\r\n", portNumber);
PrintLastErrorText();
return 0;
}
timeouts.ReadIntervalTimeout = MAXDWORD;
timeouts.ReadTotalTimeoutMultiplier = 0;
timeouts.ReadTotalTimeoutConstant = 0;
timeouts.WriteTotalTimeoutMultiplier = 0;
timeouts.WriteTotalTimeoutConstant = 0;
if(FALSE == SetCommTimeouts(*handle, &timeouts))
{
printf("ERROR: Setting timeout parameters for COM%d failed.\r\n", portNumber);
PrintLastErrorText();
return 0;
}
(*overlapped).hEvent = CreateEvent(
NULL, // default security attributes
TRUE, // manual-reset event
FALSE, // not signaled
NULL // no name
);
if(NULL == overlapped->hEvent)
{
printf("ERROR: CreateEvent for COM%d failed.\r\n", portNumber);
PrintLastErrorText();
return 0;
}
// Initialize the rest of the OVERLAPPED structure to zero.
overlapped->Internal = 0;
overlapped->InternalHigh = 0;
overlapped->Offset = 0;
overlapped->OffsetHigh = 0;
return 1;
}
int CloseSerialConnection(HANDLE* handle)
{
if(FALSE == CloseHandle(*handle))
{
printf("ERROR: Cannot close handle 0x8.8%X\r\n", *handle);
PrintLastErrorText();
return 0;
}
*handle = NULL;
return 1;
}
int ReadSerial(HANDLE* handle, LPOVERLAPPED ov, int num, char* buffer, int max_len)
{
DWORD readTotal = 0;
if(FALSE == ClearCommError(*handle, NULL, NULL))
{
printf("ClearCommError failed with error:\r\n");
PrintLastErrorText();
return 0;
}
else
{
memset(buffer, 0, max_len);
if(FALSE == ReadFile(*handle, buffer, max_len, &readTotal, ov))
{
printf("ERROR: Reading from port COM%d failed\r\n", num);
if(ERROR_IO_PENDING == GetLastError())
{
printf("I/O is pending (ReadFile)...\r\n");
if(FALSE == GetOverlappedResult(*handle, ov, &readTotal, TRUE))
{
printf("GetOverlappedResult failed with error:\r\n");
PrintLastErrorText();
return 0;
}
}
else
{
PrintLastErrorText();
return 0;
}
}
else
{
PrintCurrentDateTime();
printf("Received %d characters on port COM%d: ", readTotal, num);
PrintBufferContent(buffer, readTotal);
}
}
return 1;
}
utils.c：
#include <Windows.h>
#include <stdio.h>
#include "utils.h"
void PrintLastErrorText(void)
{
DWORD retSize;
LPTSTR pTemp = NULL;
retSize = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ARGUMENT_ARRAY, NULL, GetLastError(), LANG_NEUTRAL, (LPTSTR)&pTemp, 0, NULL);
if ((retSize > 0) &&
(pTemp != NULL))
{
printf("Last error: %s (0x%08X)\r\n", pTemp, GetLastError());
LocalFree((HLOCAL)pTemp);
}
}
void PrintCurrentDateTime(void)
{
SYSTEMTIME systime;
GetLocalTime(&systime);
printf("%04d.%02d.%02d %02d:%02d:%02d:%03d ", systime.wYear, systime.wMonth, systime.wDay, systime.wHour, systime.wMinute, systime.wSecond, systime.wMilliseconds);
}
void PrintBufferContent(char* buff, int len)
{
int i;
for(i = 0; i<len; i++)
{
printf("%02X ", buff[i]);
}
}
答案 0 :(得分：1)
您对OVERLAPPED和WaitCommEvent使用相同的ReadFile结构。尝试为每个人使用单独/独立的OVERLAPPED。
更新：忽略之前的答案。
如果您对WaitCommEvent的通话返回ERROR_IO_PENDING，则表示您没有等待它完成。而不是循环并再次调用WaitCommEvent，您需要等待操作完成（通常通过GetOverlappedResult）。
您不能让多个挂起的异步请求共享一个OVERLAPPED结构。通过在ERROR_IO_PENDING之后循环并再次调用WaitCommEvent，这正是发生的事情。