Node-RED & Touchberry Tutorial: How to get temperature from Dallas sensor

// C library headers
#include <stdio.h>
#include <string.h>
// Linux headers
#include <fcntl.h> // Contains file controls like O_RDWR
#include <errno.h> // Error integer and strerror() function
#include <termios.h> // Contains POSIX terminal control definitions
#include <unistd.h> // write(), read(), close()
#include <stdlib.h>
#include <sys/stat.h>
#include <dirent.h>
#include <errno.h>
///////////////////////////////////////////////////////////////////////////////////////
// Convert char to int
int char2int(char input)
{
  if(input >= '0' && input <= '9') {
    return input - '0';
  }
  if(input >= 'A' && input <= 'F') {
    return input - 'A' + 10;
  }
  if(input >= 'a' && input <= 'f') {
    return input - 'a' + 10;
  }
  return 0;
}
///////////////////////////////////////////////////////////////////////////////////////
void hex2bin(const char* src, char* target)
{
  while(*src && src[1])
  {
    *(target++) = char2int(*src)*16 + char2int(src[1]);
    src += 2;
  }
}
///////////////////////////////////////////////////////////////////////////////////////
int main(int argc, char* argv[]) {
  char read_buf [256];
  int fd;
  if (argc < 2) {
    printf("Usage: %s <data-hex>\n", argv[0]);
    return 1;
  }
  char buf[100];
  hex2bin(argv[1], buf);
  int buflen = strlen(argv[1]) / 2;
  // Open the serial port. Change device path as needed (currently set to an standard FTDI USB-UART cable type device)
  int serial_port = open("/dev/ttyS0", O_RDWR);
  // Create new termios struc, we call it 'tty' for convention
  struct termios tty;
  // Read in existing settings, and handle any error
  if(tcgetattr(serial_port, &tty) != 0) {
      printf("Error %i from tcgetattr: %s\n", errno, strerror(errno));
      return 1;
  }
  tty.c_cflag &= ~PARENB;
 // tty.c_cflag &= ~PARODD; // Clear parity bit, disabling parity (most common)
  tty.c_cflag &= ~CSTOPB; // Clear stop field, only one stop bit used in communication (most common)
  tty.c_cflag &= ~CSIZE; // Clear all bits that set the data size
  tty.c_cflag |= CS8; // 8 bits per byte (most common)
  tty.c_cflag &= ~CRTSCTS; // Disable RTS/CTS hardware flow control (most common)
  tty.c_cflag |= CREAD | CLOCAL; // Turn on READ & ignore ctrl lines (CLOCAL = 1)
  tty.c_lflag &= ~ICANON;
  tty.c_lflag &= ~ECHO; // Disable echo
  tty.c_lflag &= ~ECHOE; // Disable erasure
  tty.c_lflag &= ~ECHONL; // Disable new-line echo
  tty.c_lflag &= ~ISIG; // Disable interpretation of INTR, QUIT and SUSP
  tty.c_iflag &= ~(IXON | IXOFF | IXANY); // Turn off s/w flow ctrl
  tty.c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP|INLCR|IGNCR|ICRNL); // Disable any special handling of received bytes
  tty.c_oflag &= ~OPOST; // Prevent special interpretation of output bytes (e.g. newline chars)
  tty.c_oflag &= ~ONLCR; // Prevent conversion of newline to carriage return/line feed
  // tty.c_oflag &= ~OXTABS; // Prevent conversion of tabs to spaces (NOT PRESENT ON LINUX)
  // tty.c_oflag &= ~ONOEOT; // Prevent removal of C-d chars (0x004) in output (NOT PRESENT ON LINUX)
  tty.c_cc[VTIME] = 1;    // Wait for up to 1s (10 deciseconds), returning as soon as any data is received.
  tty.c_cc[VMIN] = 0;
  // Set in/out baud rate to be 9600
  cfsetispeed(&tty, B9600);
  cfsetospeed(&tty, B9600);
  // Save tty settings, also checking for error
  if (tcsetattr(serial_port, TCSANOW, &tty) != 0) {
      printf("Error %i from tcsetattr: %s\n", errno, strerror(errno));
      return 1;
  }
// Export the desired pin by writing to /sys/class/gpio/export
  int dir = open("/sys/class/gpio/gpio27", O_WRONLY);
  if (ENOENT == errno) {
    /* Directory does not exist. */
//    write(dir, "27", 2);
    fd = open("/sys/class/gpio/export", O_WRONLY);
    if (fd == -1) {
      perror("Unable to open /sys/class/gpio/export");
      exit(1);
    }
    if (write(fd, "27", 2) != 2) {
      perror("Error writing to /sys/class/gpio/export");
      exit(1);
    }
  }
  close(dir);
// Set the pin to be an output by writing "out" to /sys/class/gpio/gpio27/direction
  fd = open("/sys/class/gpio/gpio27/direction", O_WRONLY);
  if (fd == -1) {
      perror("Unable to open /sys/class/gpio/gpio27/direction");
      exit(1);
  }
  if (write(fd, "out", 3) != 3) {
      perror("Error writing to /sys/class/gpio/gpio27/direction");
      exit(1);
  }
  close(fd);
  fd = open("/sys/class/gpio/gpio27/value", O_WRONLY);
  if (fd == -1) {
      perror("Unable to open /sys/class/gpio/gpio27/value");
      exit(1);
  }
  // Toggle LED 50 ms on, 50ms off, 100 times (10 seconds)
  if (write(fd, "1\n", 2) != 2) {
    perror("Error writing to /sys/class/gpio/gpio27/value");
    exit(1);
  }
  //usleep(10000);
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
  if (write(serial_port, buf, buflen) < 0) {
	perror("Error writing to serial port");
	exit(1);
  }
int t = 10 * buflen * 1000000 / 9600;
usleep(t);
usleep(1000);
//tcdrain(serial_port);
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
  if (write(fd, "0\n", 2) != 2) {
    perror("Error writing to /sys/class/gpio/gpio27/value");
    exit(1);
  }
  usleep(5000);
  close(fd);
  // Normally you wouldn't do this memset() call, but since we will just receive
  // ASCII data for this example, we'll set everything to 0 so we can
  // call printf() easily.
  //memset(read_buf, '\0', sizeof(read_buf));
  // Read bytes. The behaviour of read() (e.g. does it block?,
  // how long does it block for?) depends on the configuration
  // settings above, specifically VMIN and VTIME
//  char* num_bytes[] = {};
//  for (int i = 0; i < sizeof(read_buf); i++){
//    num_bytes[i] = read_buf[i];
//  }
char c;
int n;
char* ptr = read_buf;
int num_bytes = 0;
do {
	n = read(serial_port, &c, 1);
	if (n < 0) {
		perror("Read  serial port fail");
		exit(1);
	} else if (n > 0) {
		*ptr++ = c;
		++num_bytes;
	}
} while (n > 0);
  // n is the number of bytes read. n may be 0 if no bytes were received, and can also be -1 to signal an error.
  if (num_bytes < 0) {
      printf("Error reading: %s", strerror(errno));
      return 1;
  }
// Here we assume we received ASCII data, but you might be sending raw bytes (in that case, don't try and
// print it to the screen like this!)
// for (int i = 0; i < num_bytes; i++) {
//  printf("Read %i bytes. Received message: %s", num_bytes, read_buf);
// }
//  for (int i = 0; i < num_bytes; i++){
//  printf("Read %i bytes. Received message: %s", num_bytes, read_buf);
//  }
//printf("Received buffer (%d): ", num_bytes);
  for (int i = 0; i < num_bytes; ++i) {
    printf("%02x", read_buf[i]);
  }
  printf("\n");
  close(serial_port);
  return 0; // success
}
///////////////////////////////////////////////////////////////////////////////////////