is WriteFile working ? C++ - c++

Question

I have to send 6 byte to a device in serial port. The port is open but the data isnt sent. I use serial port monitor to know what happen with my code(C++ Win32, Visual Studio).
I am using CreateFile
hPort = CreateFile( TEXT("COM3"),
GENERIC_READ | GENERIC_WRITE,
0,
NULL,
OPEN_EXISTING,
0,
NULL );
My code to write is:
void uart::write(char data) {
WriteFile(hPort,
(LPCVOID)data,
1,
&byteswritten,
NULL);
}
When i need execute a command in my device i call fuction sendCommand("000000010000000100000000000000000000000000000000");
void device::sendCommand(std::string command) {
int size = command.length();
char* string = (char*)command.c_str();
std::vector<char> data(command.begin(), command.end()) ;
std::cout <<"[Uart.write]>>\n";
int j=0;
for (int k = 0; k <= size - 1; k++) {
Uart.write(data[k]);
std::cout << data[k];
j++;
if (j % 8 == 0 && j!=0) { std::cout << "__byte " << j / 8 << "send___\n";
}
I use the next code like as model to write the above code win32 c++.
#using <System.dll>
using namespace System;
using namespace System::IO::Ports;
using namespace System::Threading;
void SendCommand(SerialPort^ port, Byte unit, Byte command, Int32 data);
int _tmain(int argc, _TCHAR* argv[])
{
SerialPort^ port;
Byte unit;
Byte command;
Int32 data;
// Set up serial port
port = gcnew SerialPort();
port->PortName = "COM8";
port->BaudRate = 9600;
port->DataBits = 8;
port->Parity = Parity::None;
port->StopBits = StopBits::One;
port->Handshake = Handshake::None;
// Open port
port->Open();
// Home device 1
SendCommand(port, 1, CMD_HOME, 0);
WaitForReply(port, 1, CMD_HOME, unit, command, data);
// Close port
port->Close();
return 0;
}
void SendCommand(SerialPort^ port, Byte unit, Byte command, Int32 data)
{
array<Byte>^ packet = gcnew array<Byte>(6);
gcnew array<Byte>
packet[0] = unit;
packet[1] = command;
packet[2] = data & 0xFF;
packet[3] = (data >> 8) & 0xFF;
packet[4] = (data >> 16) & 0xFF;
packet[5] = (data >> 24) & 0xFF;
port->Write(packet, 0, 6);
}
I would like find something like array<Byte>^ packet = gcnew array<Byte>(6);
gcnew array<Byte>
packet[0] = unit; .......... in C++. I think my problem is that.

Answer 1

void uart::write(char data) {
WriteFile(hPort,
(LPCVOID)data,
1,
&byteswritten,
NULL);
}
are you understand what you doing here ? you pass buffer address in range 0-255 which is of course invalid and not point to your actual data. when kernel check your buffer - exception STATUS_ACCESS_VIOLATION raised , which converted to ERROR_NOACCESS by win32. this error code must return GetlastError() after your call to WriteFile return false.
you need next function for write 1 byte:
DWORD uart::write(char data) {
DWORD byteswritten;
return WriteFile(hPort,
&data,
sizeof(data),
&byteswritten,
NULL) ? NOERROR : GetLastError();
}
not sure are after this all will be worked (are no another errors in code) but this fix is must be done