How to debug C program on microcontroller

Question

this is my first C code. So, I wrote a code which gets values from 5 potentiometers from a microcontroller(pololu maestro) via serial port and then moves 10 servos from the 5 pot values. When I compile and run the code in CodeBlocks, there are no errors or warnings, but when I run it crashes. It says that my .exe file has stopped running.

// Uses POSIX functions to send and receive data from a Maestro.
// NOTE: The Maestro's serial mode must be set to "USB Dual Port".
// NOTE: You must change the 'const char * device' line below.

#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include <math.h>

#ifdef _WIN32
#define O_NOCTTY 0
#else
#include <termios.h>
#endif

// Gets the position of a Maestro channel.
// See the "Serial Servo Commands" section of the user's guide.
int maestroGetPosition(int fd, unsigned char channel)
{
  unsigned char command[] = {0x90, channel};
  if(write(fd, command, sizeof(command)) == -1)
  {
    perror("error writing");
    return -1;
  }

  unsigned char response[2];
  if(read(fd,response,2) != 2)
  {
    perror("error reading");
    return -1;
  }

  return response[0] + 256*response[1];
}

// Sets the target of a Maestro channel.
// See the "Serial Servo Commands" section of the user's guide.
// The units of 'target' are quarter-microseconds.
int maestroSetTarget(int fd, unsigned char channel, unsigned short target1, unsigned short target2, unsigned short target3, unsigned short target4, unsigned short target5, unsigned short target6, unsigned short target7, unsigned short target8, unsigned short target9, unsigned short target10)
{
  unsigned char command[] = {170, 12, 31, 10, channel, target1 & 0x7F, target1 >> 7 & 0x7F, target2 & 0x7F, target2 >> 7 & 0x7F, target3 & 0x7F, target3 >> 7 & 0x7F, target4 & 0x7F, target4 >> 7 & 0x7F, target5 & 0x7F, target5 >> 7 & 0x7F, target6 & 0x7F, target6 >> 7 & 0x7F, target7 & 0x7F, target7 >> 7 & 0x7F, target8 & 0x7F, target8 >> 7 & 0x7F, target9 & 0x7F, target9 >> 7 & 0x7F, target10 & 0x7F, target10 >> 7 & 0x7F};
  if (write(fd, command, sizeof(command)) == -1)
  {
    perror("error writing");
    return -1;
  }
  return 0;
}

/////////////////////////////////////////////////////////////////////////////////

int main()
{
  // Open the Maestro's virtual COM port.
  const char * device = "\\\\.\\COM8";  // Windows, "\\\\.\\COM6" also works
  //const char * device = "/dev/ttyACM0";  // Linux
  //const char * device = "/dev/cu.usbmodem00034567"; // Mac OS X
  int fd = open(device, O_RDWR | O_NOCTTY);
  if (fd == -1)
  {
    perror(device);
    return 1;
  }

#ifndef _WIN32
  struct termios options;
  tcgetattr(fd, &options);
  options.c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
  options.c_oflag &= ~(ONLCR | OCRNL);
  tcsetattr(fd, TCSANOW, &options);
#endif

int count1;
int b_pos;
int b_l;
int x[10];
int rel;
int count2;
int count3;
int count4;
int x0[10];
int x1;
int x2;
int x3;
int x4;
int x5;

for (count1=1; count1<=1000; count1++){

    x1 = maestroGetPosition(fd, 0);
    x2 = maestroGetPosition(fd, 1);
    x3 = maestroGetPosition(fd, 2);
    x4 = maestroGetPosition(fd, 3);
    x5 = maestroGetPosition(fd, 4);

/////////////////////////////////////////////////////////////////////////////////

    if(x1 == 0){
        b_pos = 0;
    }else if( (x1 <= 102) && (x1 > 0) ){
        b_pos = 1;
    }else if( (x1 <= 102) && (x1 > 0) ){
        b_pos = 2;
    }else if( (x1 <= 102) && (x1 > 0) ){
        b_pos = 3;
    }else if( (x1 <= 102) && (x1 > 0) ){
        b_pos = 4;
    }else if( (x1 <= 102) && (x1 > 0) ){
        b_pos = 5;
    }else if( (x1 <= 102) && (x1 > 0) ){
        b_pos = 6;
    }else if( (x1 <= 102) && (x1 > 0) ){
        b_pos = 7;
    }else if( (x1 <= 102) && (x1 > 0) ){
        b_pos = 8;
    }else if( (x1 <= 102) && (x1 > 0) ){
        b_pos = 9;
    }else if( (x1 <= 102) && (x1 > 0) ){
        b_pos = 10;
    }

/////////////////////////////////////////////////////////////////////////////////

    if(b_pos != 0){
        if (x2 <= 255){
            b_l = 1;
        }else if( (x2 <= 510) && (x2 >= 256) ){
            b_l = 2;
        }else if( (x2 <= 765) && (x2 >= 511) ){
            b_l = 3;
        }else{
            b_l = 4;
        }
    }

/////////////////////////////////////////////////////////////////////////////////

    x3 = (x3*0.988)+992;
    for (count4 = 1; count4 <= 10; count4++){
        x[count4] = x3;
    }

/////////////////////////////////////////////////////////////////////////////////

    if(b_pos != 0){
        x4 = (x4*0.39)-200;
        x5 = (x5*0.098);
        x[b_pos] = x[b_pos] + x4;
        rel = 1;

        if (x4 >= 0){
            for (count2 = b_pos; count2<=( (b_pos) + (b_l) ); count2++){
                        if ((count2 > 0) && (count2 < 11)){
                            x[count2] = x[count2] + x4  + ( (x4/abs(x4))*(x5*rel) );
                            rel += 1;
                        }
            }
            for (count2 = b_pos; count2<=( (b_pos) - (b_l) ); count2--){
                        if ((count2 > 0) && (count2 < 11)){
                            x[count2] = x[count2] + x4  + ( (x4/abs(x4))*(x5*rel) );
                            rel += 1;
                        }
            }
        }
    }

/////////////////////////////////////////////////////////////////////////////////


    for (count3 = 1; count3 <= 10; count3++){
        if (x[count3] < 992){
            x[count3] = 992;
        }
        if (x[count3] > 2000){
            x[count3] = 2000;
        }
        x0[count3] = (x[count3] * 4);
    }


  //int target = (position < 6000) ? 7000 : 5000;
  //printf("Setting target to %d (%d us).\n", target, target/4);
  maestroSetTarget(fd, 7, x0[1], x0[2], x0[3], x0[4], x0[5], x0[6], x0[7], x0[8], x0[9], x0[10]);

}

return 0;

close(fd);

}

Answer 1

You have

x[b_pos] = x[b_pos] + x4;

where b_pos could have a value of 10, but x can only hold 10 elements, accessing then 11th element causes undefined behavior which in turn could make your program crash.