Serial communication not working. Readfile goes wrong

Question

After hours of browsing and reading, I still can't figure out why my code isn't working. I saw similar code snippets on different websites, but I can't seem to get it to work. The writing part is working, but the reading goes wrong. Every 'real character' is followed by three null terminators. Writing a string of 19 characters works and the FPGA I am using gives the correct data on the display. The FPGA should reverse the input and send this pack to the serial port. In the Hyperterminal this is working without any problem.

Can someone maybe point me on my mistake and tell me what I am doing wrong?

Thanks in advance =)

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <time.h>
#include    <commdlg.h>
//#include  <windef.h>
#define    BUFFERLENGTH 19

void writeToSerial(char *line, HANDLE hSerial, DWORD dwBytesWritten);
void printBuffer(char * buffRead, DWORD dwBytesRead);


int main(){
    HANDLE hSerial;
    COMMTIMEOUTS timeouts;
    COMMCONFIG dcbSerialParams;
    char *line, *buffWrite, *buffRead;
    DWORD dwBytesWritten, dwBytesRead;
    /* Create a handle to the serial port */    
    hSerial = CreateFile("COM3",
                            GENERIC_READ | GENERIC_WRITE,
                            0,
                            NULL,
                            OPEN_EXISTING,
                            FILE_ATTRIBUTE_NORMAL,
                            NULL);
    /* Check if the handle is valid */                        
    if(hSerial == INVALID_HANDLE_VALUE){
       if(GetLastError() == ERROR_FILE_NOT_FOUND){
          printf("Serial port does not exist \n");
       }else{
          printf("Port occupied. Please close terminals!\n");
       }
    }else{
       printf("Handle created\n");    
       /* Check the state of the comm port */
       if(!GetCommState(hSerial, &dcbSerialParams.dcb)){
          printf("Error getting state \n");
       }else{
          printf("Port available\n"); 
          /* Configure the settings of the port */
          dcbSerialParams.dcb.DCBlength = sizeof(dcbSerialParams.dcb);
          /* Basic settings */    
          dcbSerialParams.dcb.BaudRate = CBR_57600;
          dcbSerialParams.dcb.ByteSize = 8;
          dcbSerialParams.dcb.StopBits = ONESTOPBIT;
          dcbSerialParams.dcb.Parity = NOPARITY;
          /* Misc settings */
          dcbSerialParams.dcb.fBinary = TRUE;
          dcbSerialParams.dcb.fDtrControl = DTR_CONTROL_DISABLE;
          dcbSerialParams.dcb.fRtsControl = RTS_CONTROL_DISABLE;
          dcbSerialParams.dcb.fOutxCtsFlow = FALSE;
          dcbSerialParams.dcb.fOutxDsrFlow = FALSE;
          dcbSerialParams.dcb.fDsrSensitivity= FALSE;
          dcbSerialParams.dcb.fAbortOnError = TRUE;
          /* Apply the settings */
          if(!SetCommState(hSerial, &dcbSerialParams.dcb)){
            printf("Error setting serial port state \n");
          }else{
            printf("Settings applied\n");  
            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");
            }else{
                /* Ready for communication */
                line = "Something else\r";
                //****************Write Operation*********************//
                writeToSerial(line, hSerial, dwBytesWritten);
                //***************Read Operation******************//
                if(ReadFile(hSerial, buffRead, BUFFERLENGTH, &dwBytesRead, NULL)){
                   printBuffer(buffRead, dwBytesRead);                     
                }
             }          
          }
       }
    }
    CloseHandle(hSerial);
    system("PAUSE");
    return 0;

}
void printBuffer(char * buffRead, DWORD dwBytesRead){
     int j;
     for(j = 0; j < dwBytesRead; j++){
         if(buffRead[j] != '\0'){    
           printf("%d: %c\n", j, buffRead[j]);
         }
     }   
}

void writeToSerial(char *line, HANDLE hSerial, DWORD dwBytesWritten){
    WriteFile(hSerial, line, 19, &dwBytesWritten,NULL);
    if(dwBytesWritten){
       printf("Writing success, you wrote '%s'\n", line);
    }else{
       printf("Writing went wrong =[\n");      
    }
}

Answer 1

Hyper terminal probably doesn't display null characters so it's possible that your fpga is actually sending them.

You could try testing it with Br@y Terminal in hex mode, or looking at the line with an oscilloscope.

Answer 2

In this line:

if(ReadFile(hSerial, buffRead, BUFFERLENGTH, &dwBytesRead, NULL))

the buffRead parameter is an uninitialised pointer. Change the declaration to:

char *line, *buffWrite, buffRead [BUFFERLENGTH+1];