Sharing variables across classes

Adampultz

I often need access to information such as sample rate, number of inputs, etc, in several of the classes I have written for my projects, and initialising them for every class in a function such as foo.init(int sampleRate, int numInputs, etc.) seems redundant. While defining macros in my render.cpp filer or a header file could do the trick, I feel it would be neater to be able to initialise the values during compilation and would allow for the possibility of changing values during runtime.

I tried creating a header file, assigning the variables as public, and then pass the sample rate from render.cpp (I use JUCE for developing code so I haven't actually tested this on the Bela yet, so render.cpp would equal the MainComponent file in a JUCE project):

class GlobalInfo {
public:

GlobalInfo(){}

void setup(int sampleRate){
    g_SampleRate = sampleRate;
    g_SampleDur = 1.0 / sampleRate;
   g_Nyquist = sampleRate / 2;
};
   
int g_SampleRate;
double g_SampleDur;
int g_Nyquist;
};

I then make my classes inherit from GlobalInfo, like this (header file):

class RMS : public GlobalInfo { //code }

In the RMS.cpp file:

void RMS::init(float frequency) { double sampleDurTest = g_sampleDur; int sampleRateTest = g_sampleRate; ym1_ = 0.0f; b1_ = expf(-2.0f * (float)M_PI * (frequency * g_sampleDur)); a0_ = 1.0f - b1_; }

But despite initialising the variables in setup, in the child classes, they are 0-initialised.

giuliomoro

You need to mark the class variables that you want to share across instances as having static storage, otherwise each instance will have its own copy of the variable.

Adampultz

I am unsure of how to do that. I made a minimal example here :

#include <iostream>
 
class GlobalInfo {

public:

GlobalInfo(){}    
static void setup(int sampleRate){
g_SampleRate = sampleRate;
};
    
static int g_SampleRate;
};

class Foo : public GlobalInfo {
public:
Foo(){}

static void init(){
    int test = GlobalInfo::g_SampleRate;
}    
};

int main(int argc, const char * argv[]) {

GlobalInfo::setup(48000);
Foo::init();
return 0;
}`

But I get "Undefined symbol: GlobalInfo::g_SampleRate" and "Linker command failed with exit code 1 (use -v to see invocation)".

How do I initialise the static variable and use it in a different class, or is that even an option? I've searched the internet for solution but I am still not clear on how static variables work.

giuliomoro

Adampultz Undefined symbol: GlobalInfo::g_SampleRate" and "Linker command failed with exit code 1 (use -v to see invocation

In exactly one cpp file which includes this header you further need to define:

int GlobalInfo::g_SampleRate;

Adampultz

Now it works, thanks so much! This is going to save me lots of code and hassle.

Ward

I have one header with all sorts of often used functions and global variables:

namespace Formulas {
	const double samplerate = 48000.0;
	const unsigned bufsize = 64;
	const double inverseSamplerate = 1.0 / samplerate;

	inline float dbtoa(float db) {
		return powf_neon(10, (db / 20));
	}
	inline float atodb(float amp) {
		return 20.0f * log10f_neon(amp);
	}
	// etc
}