How to pass a filename to a function? What type of variable is the filename?

Question

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)) {
 sd.initErrorHalt();
 }
 setTemperature(7);
 setFanSpeed(4);
}
void setTemperature(int t) {
 SdFile rdfile("temperature.txt", O_WRITE);
 rdfile.rewind();
 rdfile.println(t);
 rdfile.close();
}
void setFanSpeed(int t) {
 SdFile rdfile("fanspeed.txt", O_WRITE);
 rdfile.rewind();
 rdfile.println(t);
 rdfile.close();
}

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)
{
 ...
}

• Jerry: 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: 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. :)
• Ignacio Vazquez-Abrams: @Jerry: That's the correct way to do it in C++. en.wikipedia.org/wiki/Reference_%28C%2B%2B%29