Reading a value from file in c

readtempfromfile.c

/*
  This example program reads a value from a file. This file can be updated
  from another program, while this main program never needs to stop.
  
  gcc -O2 -Wall -o readtempfromfile readtempfromfile.c
  
*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

float read_temp_from_file() {
  FILE *fp;
  char buff[5]; // 5 characters ought to be sufficient.
  fp = fopen("temp.txt", "r");
  fscanf(fp, "%s", buff);
  fclose(fp);

  float ftemp = atof(buff);

  return ftemp;
}

int main (int argc, char **argv) {
  //  printf("Reading temperature from file: temp.txt\n");

  float temp = read_temp_from_file();
  while (1) {
    printf("Current temperature: %0.2f\n", temp);
    temp = read_temp_from_file();
    sleep(1);
  }
  return 0;
}