Com Port C ++读取0xFF

Question

I'm trying to read/write from a com port. When I open the Com Port I make it Non overlapped. Everything works fine, but when I read a 0xFF byte it sees it like an EOF and finishes the read. Can I make a Non overlapped read 0xFF?

Here is my code:

//Opening the com port:

hComm = CreateFile( s.c_str(),                      // COM PORT
                    GENERIC_READ | GENERIC_WRITE,   //
                    0,                              // exclusive access
                    NULL,                           // no security
                    OPEN_EXISTING,                  // must be a port
                    0 ,                             // async i/o
                    NULL);                          // 
//Port init:
void initPort(int baud)
{
    uart_baud = baud;
    DCB dcb;
    dcb.DCBlength = sizeof(DCB);
    GetCommState(hComm, &dcb); // read current config
    dcb.BaudRate = baud;
    dcb.ByteSize = 8;
    dcb.StopBits = ONESTOPBIT;
    dcb.Parity = NOPARITY;
    dcb.fParity = FALSE;

    SetCommState(hComm, &dcb);
}

//Reading:(PS: private: char rx_packet[1024]; int rx_size;)
int readByte(int timeout)
{
    COMMTIMEOUTS CommTimeOuts;

    CommTimeOuts.ReadIntervalTimeout = 1;
    CommTimeOuts.ReadTotalTimeoutMultiplier  = timeout;
    CommTimeOuts.ReadTotalTimeoutConstant = 0;
    CommTimeOuts.WriteTotalTimeoutMultiplier = 0;
    CommTimeOuts.WriteTotalTimeoutConstant   = 0;

    SetCommTimeouts(hComm, &CommTimeOuts);

    char  byte;
    DWORD bytes = 0;

    if (ReadFile(hComm, &byte, 1, &bytes, NULL))
    {
        return bytes == 1 ? byte : -1;
    }
    return -1;
}

void readPacket(void)
{
    int data_read;
    bool first_read = true;
    rx_size = 0;
    DWORD dwEventMask;
    DWORD ERR = 0;

    if (!SetCommMask(hComm, EV_RXCHAR)) return;
    if (!WaitCommEvent(hComm, &dwEventMask, NULL)) return;

    while (rx_size < MAX_PACKET_SIZE)
    {
        data_read = readByte(first_read ? 200 : 50);
        first_read = false;

        if (data_read == -1)return;

        rx_packet[rx_size] = (char)data_read;
        rx_size++;
    }
}

//Writing port:
bool writeByte(char byte)
{
    DWORD bytes = 0;
    WriteFile(hComm, &byte, 1, &bytes, NULL);
    return bytes == 1 ? true : false;
}

void RvcCommUART::writePacket(BYTE *data , UINT16 size)
{
    int tx_index = 0;
    while (tx_index < size)
    {
        if (writeByte(data[tx_index]) == false) return;

        tx_index++;
    }
}

Answer 1

It seems that your char is signed (its signedness is implementation-dependent), so 0xFF is -1 .

Use unsigned char to represent "bytes".