Log to SD function from homebrew temperature logger

homebrew_temperature_logger_log_file.c

/*
 * Logs current temperature data to SD card.
 * Note that the global variable "filename" must be initialised
 * File format is:
 * datestring,sensor0_name,temp0,sensor1_name,temp1,sensor2_name,temp2
 * datestring,sensor0_name,temp0,sensor1_name,temp1,sensor2_name,temp2
 */
byte log_temps(char *date_str){
  File f = SD.open(filename, FILE_WRITE);
  if(f) {
    f.print(date_str);
    for(byte a=0; a<num_sensors; a++){
      f.print(",");
      f.print(probe_name_array[a]);
      f.print(",");
      f.print(temp_array[a]);
    }
    f.println(""); 
    f.close();
  }else{
    state=ERR;
    error_code = ERROR_LOGGING;
  }
  return(ERROR_NONE);  
}