serial port Reading in c++ - c++

Question

I am trying to write code in c++ to write and read from serial port i wrote the following code and i am now trying to test this by making loop back on USB to serial cable and when i write any thing except zero i read it successfully but when write zero the program stops reading and doesnot read any thing after the zero and give me zeroes when displaying the read buffer (in this program it displays zeroes for reading buffer but if i write any thing like making writing loop write "words=127-i" the reader buffer will display all i write till it reaches zero) plz any help quickly
#include <windows.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <commdlg.h>
#include <iostream>
//#include <windef.h>
using namespace std;
int nread,nwrite;
void main()
{
HANDLE hSerial;
COMMTIMEOUTS timeouts;
COMMCONFIG dcbSerialParams;
char words[128], *buffWrite;
DWORD dwBytesWritten, dwBytesRead;
hSerial = CreateFile(TEXT("COM1"),GENERIC_READ |GNERIC_WRITE,0,NULL,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,NULL);
if(hSerial == INVALID_HANDLE_VALUE)
{
if (GetLastError() == ERROR_FILE_NOT_FOUND)
{
printf(" serial port does not exist \n");
}
printf(" some other error occured. Inform user.\n");
}
// DCB dcbSerialParams ;
//GetCommState( hSerial, &dcbSerialParams.dcb);
if (!GetCommState(hSerial, &dcbSerialParams.dcb))
{
printf("error getting state \n");
}
dcbSerialParams.dcb.DCBlength = sizeof(dcbSerialParams.dcb);
dcbSerialParams.dcb.BaudRate = CBR_2400;
dcbSerialParams.dcb.ByteSize = 8;
dcbSerialParams.dcb.StopBits = ONESTOPBIT;
dcbSerialParams.dcb.Parity = NOPARITY;
dcbSerialParams.dcb.fBinary = TRUE;
dcbSerialParams.dcb.fDtrControl = DTR_CONTROL_ENABLE;
dcbSerialParams.dcb.fRtsControl = RTS_CONTROL_ENABLE;
dcbSerialParams.dcb.fOutxCtsFlow = TRUE;
dcbSerialParams.dcb.fOutxDsrFlow = TRUE;
dcbSerialParams.dcb.fDsrSensitivity= FALSE;
dcbSerialParams.dcb.fAbortOnError = TRUE;
if(!SetCommState(hSerial, &dcbSerialParams.dcb))
{
printf(" error setting serial port state \n");
}
SetCommMask( hSerial,EV_RXCHAR);
GetCommTimeouts(hSerial,&timeouts);
//COMMTIMEOUTS timeouts = {0};
timeouts.ReadIntervalTimeout = 50;
timeouts.ReadTotalTimeoutConstant = 50;
timeouts.ReadTotalTimeoutMultiplier = 10;
timeouts.WriteTotalTimeoutConstant = 50;
timeouts.WriteTotalTimeoutMultiplier= 10;
if(!SetCommTimeouts(hSerial, &timeouts))
{
printf("error setting port state \n");
}
// printf("This is a string to be written to serial port COM1 \n\n\n");
//****************Write Operation*********************//
//words = "This is a string to be written to serial port COM1";
//dwBytesWritten=1;
cout<<"Data written to write buffer is \n";
for(int i=0;i<128;i++)
{
words[i]=i;
cout<<(int)words[i]<<",";
}
cout<<endl;
nwrite = strlen(words);
buffWrite = words;
dwBytesWritten = 0;
if (!WriteFile(hSerial, buffWrite, nwrite, &dwBytesWritten, NULL))
{
printf("error writing to output buffer \n");
}
//***************Read Operation******************//
char buffsRead[128]="0",*buffRead;
dwBytesRead = 0;
nread = strlen(buffsRead);
buffRead = buffsRead;
//ReadFile(hSerial, buffRead, nread, &dwBytesRead, NULL);
if (!ReadFile(hSerial, buffRead, nread, &dwBytesRead, NULL))
{
printf("error reading from input buffer \n");
}
// printf("Data read from read buffer is \n %s \n",(int)buffsRead);
cout<<"Data read from read buffer is \n ";
for(int j=0;j<128;j++)
{
cout<<(int)buffsRead[j]<<",";
}
cout<<endl;
CloseHandle(hSerial);
// system("PAUSE");
}

Answer 1

The problem is in your calculation of the number of bytes to write. You have
nwrite = strlen(words);
and that does not work on binary data, because strlen stops at the first '\0' (NUL character).
Just adjust nwrite inside your loop, so that it ends up with the number of characters added. Replace
words[i]=i;
with
words[nwrite++] = i;
and get rid of nwrite = strlen(words); and things will work better.