How do I implement reverse enumeration?

Question

Basically I'm trying to output a string based upon a value in an array, the following code is what I have come up with to achieve my desired result, but I have a feeling that there is a better way to do it.

String day(int day) {
 if (day == 1) return "Sunday"; 
 if (day == 2) return "Monday";
 if (day == 3) return "Tuesday";
 if (day == 4) return "Wednesday";
 if (day == 5) return "Thursday";
 if (day == 6) return "Friday";
 if (day == 7) return "Saturday";
 else return "Undefined";
}
void setup() {
 Serial.begin(57600);
 while (!Serial);
 Serial.println(day(1));
}
void loop() {
;
}

This prints "Sunday" in the Serial monitor

I would appreciate any input on how to optimize this code, thank you!

• Filip Franik: Just one little thing to add to all the answers. Since this is "enumeration" I suggest substituting the magical int number with a refactor friendlyenum.

Answer 1

My method makes use of the __FlashStringHelper class:

// For convenience:
typedef const __FlashStringHelper *FlashString;
FlashString reverseEnum(int val) {
 switch (val) {
 case 0: return F("Option zero");
 case 1: return F("Option one");
 case 2: return F("Option two");
 default: return F("Invalid Enum");
 }
}

Printing now is as simple as:

Serial.println(reverseEnum(2));

Because it's a "flash string" the print function is overloaded properly and it performs the proper PROGMEM reading.

You can, of course, assign to a FlashString:

FlashString myString = reverseEnum(2);
Serial.println(myString);

Or if you don't want to use a typedef you can use the raw type:

const __FlashStringHelper *myString = reverseEnum(2);
Serial.println(myString);

It's just much cleaner to use a typedef.

• H3xx1st: Thanks for the info, I was really hoping for a way to use the enum, forwards and backwards without having to code out the reverse.
• Majenko: You could possibly craft something really horrible and complex with many layers of preprocessor macros, but it would be nasty and hard to understand. So don't. ;)

Answer 2

I'm no expert, but I imagine something along these lines would work:

char* day(int day) {
 static char* dayName[7] = {"Sunday", "Monday", .... };
 if (day > 0 && day < 8) {
 return dayName[day-1];
 } 
 else
 return "Undefined";
 }
}

In any case, I'll be interested to hear why it's wrong (-:

• Duncan C: Yeah, an array of char* C strings seems better than a long switch statement. (Voted)
• Edgar Bonet: Pointers to string literals should be const char* rather than char *.
• Jim Mack: @EdgarBonet - Curious - what's the advantage of const here? Is it style, speed, storage...?
• Edgar Bonet: Correctness. In C++, you are not allowed to modify the contents of a string literal.