Skip class / methods that are not defined?

Using Arduino Programming Questions
1

This may sound like an odd question, but perhaps there's a solution I am missing.

I've written some code for an MP3 Player module that many other people are using. I upgraded my MP3 player, and unfortunately, its library is not backwards compatible. Short of creating two versions of my code, I am trying to load the correct library with a preprocessor conditional (which works just fine), however, any reference to the older MP3 library / class / methods breaks with "undeclared" errors.

Is there some hack or way around this? Below is a snippet of code hopefully illustrating the issue... the error comes from line "DFPlayer.EQ(DFPLAYER_EQ_ROCK)" because the newer version of the library doesn't include the EQ method

#define MP3_PLAYER_TYPE 1 //set to 1 for Mini Pro or to 0 for Mini

#if MP3_PLAYER_TYPE > 0
byte mp3_player = 1;
#include <DFRobot_PLAY.h>
DFRobot_PLAY DFPlayer;
#else
byte mp3_player = 0;
#include <DFRobotDFPlayerMini.h>
DFRobotDFPlayerMini DFPlayer;
#endif

void setup() {

if (mp3_player == 1) {
DFPlayer.setPlayMode(DFPlayer.SINGLE);
DFPlayer.setPrompt(false);
DFPlayer.switchFunction(DFPlayer.MUSIC);
sounds_sd = DFPlayer.getTotalFile();
} else {
DFPlayer.EQ(DFPLAYER_EQ_ROCK);
sounds_sd = DFPlayer.readFileCounts();
}

}

2

You can't have code that will get compiled using the functions from the wrong library. You will need to use the same #if pattern in setup that you used to control the library include.

You might want to hide all that stuff in your own class that has a standardized set of functions each of which uses the appropriate library function controlled by #if.

1 Like
3

thanks for the response!

I was afraid of that, and makes sense - it can't compile if the methods don't exist.

do you mean I can use the #if structure within code, too, and not just as preprocessor?

otherwise, yes, I guess I will need to class it all out, else make other uses comment / uncomment the appropriate code (but that's lazy and unfair of me! lol)

4

What do you mean "within code"? You would just be using the same type of macro sequences to select the proper calls within a function rather than for selecting which global variables to define. But it's still the preprocessor ... not the compiler and not at runtime.

5

I meant exactly that... "within code" meaning anything in loop() or functions - I thought maybe the preprocessor #if structure could only be used in header of code.

so I can do something like this within setup, loop, or my own functions?

#ifndef DFPlayer.EQ()
//its not defined, so other player class is loaded
DFPlayer.setPlayMode(DFPlayer.SINGLE);
DFPlayer.setPrompt(false);
DFPlayer.switchFunction(DFPlayer.MUSIC);
sounds_sd = DFPlayer.getTotalFile();
#else
DFPlayer.EQ(DFPLAYER_EQ_ROCK);
sounds_sd = DFPlayer.readFileCounts();
#endif

6

You can use preprocessor directives wherever you like.

1 Like
7

That solves that, then! I assumed since I can't use a normal if statement outside of setup, loop, or functions, that I couldn't use preprocessor directives inside of those.... silly assumption, I should've just tried it lol

thanks so much for the help, all!

8

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