In the example below, I have two functions that write numbers to two different files on an SD card. I'm using the SdFat library.

Is there any way I can combine the two functions into one, so that I can call (for example): writeToFile(int t, FileName "filename1.txt");?

In the example below, to write a value to the "temperature.txt" file, I would like to be able to call: writeToFile(7, "temperature.txt"); In my sketch I have about a dozen functions that are writing to a dozen different files, so it would be very handy to be able to combine them into one function.

I think the main part I'm stuck on is I have no idea what the filename variable would be, or how to pass the filename to the function.

#include <SdFat.h>
SdFat sd;

void setup() {
  if (!sd.begin(chipSelect, SPI_HALF_SPEED)) {


void setTemperature(int t) {
  SdFile rdfile("temperature.txt", O_WRITE);

void setFanSpeed(int t) {
  SdFile rdfile("fanspeed.txt", O_WRITE);

1 Answer 1


String literals are of type const char *. Ordinary char *s can be passed to it though; the const means that the compiler will make sure that the function doesn't attempt to change the contents.

void setFileParameter(const char *filename, int value)
  • Thanks! It worked! I had assumed I'd be able to do the next part on my own, but ran into a smaller problem. I have another function to read the parameter from a file, so for example: readFileParameter(const char *filename, int value). I would like to call: readFileParameter("temperature.txt", currentTemp);, and have it store the value from the file into the integer currentTemp. What would I have to use instead of "int value", in order for it to change a global variable (like currentTemp)? I'm sorry that this is probably very basic stuff that I'm missing.
    – Jerry
    Commented Aug 6, 2015 at 16:59
  • I think I might've figured out my 2nd problem on my own. It seems to be working if I declare the function like this: void readFile(const char *filename, int &value). I guess the '&' causes it to modify the variable that is passed to it? It's a little too complex for my current understanding, but so far it seems to work. It would be nice if anyone points out if it's incorrect. :)
    – Jerry
    Commented Aug 6, 2015 at 18:03
  • 1
    @Jerry: That's the correct way to do it in C++. en.wikipedia.org/wiki/Reference_%28C%2B%2B%29 Commented Aug 6, 2015 at 18:05

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