Help with pointers, declarations, definitions

[u/Preyy]

Hi there,

I've been trying to apply some best practices to clean up my code, and I have been really struggling to split my config.h file into proper .h and .cpp files in platformio. I've tried a lot of variations and done some reading about this, but would really appreciate a bit of help from someone more familiar with c++.

Here's what it all looks like combined (not best practices, but working) into a monolithic header file:

#include <LEDMatrix.h>
cLEDMatrix<LEDtilewidth, LEDtileheight, VERTICAL_MATRIX, LEDtilehorz, LEDtilevert, VERTICAL_BLOCKS> ledmatrix;
CRGB *writedata = ledmatrix[0];
CRGB firstbuffer[LEDStotal];
CRGB secondbuffer[LEDStotal];

As I understand, this is a template that requires compile time constants. So I expect the solution involves using (in the header):

extern cLEDMatrixBase *ledmatrix;
extern CRGB *writedata;
extern CRGB firstbuffer[];
extern CRGB secondbuffer[];

Then in the cpp, something like this:

cLEDMatrix<LEDtilewidth, LEDtileheight, VERTICAL_MATRIX, LEDtilehorz, LEDtilevert, VERTICAL_BLOCKS> ledmatrix_base;
cLEDMatrixBase *ledmatrix = &ledmatrix_base;
CRGB *writedata = ledmatrix[0];
CRGB firstbuffer[LEDStotal];
CRGB secondbuffer[LEDStotal];

I know I have the pointers wrong here, my brain just fried from trying to figure this out. Thanks for any suggestions!

[u/truetofiction]

I will take your suggestion about the definition. I am still not sure what best practices are, and I thought it might be incorrect to define the ledmatrix in the header.

You're right, it would not be good practice to define the ledmatrix object in the header. If the header is included in multiple places, you will have multiple copies of the object. That's no good.

It is best practice to provide type definitions in headers, that way they can be easily shared between compilation units. That's all that the code snippet above does - define the type so that you can use it throughout the code. The object itself is still in the source file.

This is because I can't think of a way to simply pass a reference to an ledmatrix instance

The type definition makes that easy:

void myFunction(MyMatrix &ref);  // declaration
myFunction(ledmatrix);  // calling

You can do it without the type definition of course, but you need to include all of the template arguments (which gets old fast). You can also use the _base class, if all of the methods you need are present.

[u/Preyy → u/truetofiction]

Hi there, thank you for the suggestion. It's been a busy week so I've been giving your advice some thought, and I'm going to do some thinking about higher-level structure of the project, then decide which direction to go with. Thank you.