undefined reference for external library (c based)

Hi! I'm attempting to load a trained model as-per this library -> https://github.com/f0uriest/keras2c

So far I can clone the Github to my Bela in a fresh project (MYPROJECT), compile the test code according to the instructions (https://f0uriest.github.io/keras2c/usage.html) using the example files provided https://github.com/f0uriest/keras2c/tree/master/example) and run that program successfully on my command line on the Bela board.

Where I fail is setting up my render.cpp to do the same thing, and I'm convinced it's due to linking issues (or maybe some c vs. c++ thing?). When I load a model in render.cpp (similar to https://github.com/f0uriest/keras2c/blob/master/example/example_test_suite.c)

Which returns this error:

example.c:(.text+0x840): undefined reference to k2c_dense(k2c_tensor*, k2c_tensor const*, k2c_tensor const*, k2c_tensor const*, void (*)(float*, unsigned int), float*)'
example.c:(.text+0x882): undefined reference tok2c_dense(k2c_tensor, k2c_tensor const, k2c_tensor const, k2c_tensor const, void ()(float, unsigned int), float)'
example.c:(.text+0x8fc): undefined reference to k2c_lstm(k2c_tensor*, k2c_tensor const*, float*, k2c_tensor const*, k2c_tensor const*, k2c_tensor const*, float*, int, int, void (*)(float*, unsigned int), void (*)(float*, unsigned int))'
example.c:(.text+0x930): undefined reference tok2c_dense(k2c_tensor, k2c_tensor const, k2c_tensor const, k2c_tensor const, void ()(float, unsigned int), float)'
collect2: error: ld returned 1 exit status

I've tried to fix the linking by using this command (inspired by a fix in the references + the instructions from keras2c repo):

make -C ~/Bela PROJECT=MYPROJECT COMPILER=gcc CFLAGS="-I/root/Bela/projects/MYPROJECT/ -std=c99" LDFLAGS="-L/root/Bela/projects/MYPROJECT/include" LDLIBS="-lkeras2c -lm /root/Bela/projects/MYPROJECT/example.c"

Notably, if I exclude the example.c reference, i get an issue with having undefined references to things defined in that file:

/root/Bela/projects/MYPROJECT/render.cpp:674: undefined reference to example_initialize()'
/root/Bela/projects/MYPROJECT/render.cpp:676: undefined reference toexample(k2c_tensor, k2c_tensor)'
/root/Bela/projects/MYPROJECT/render.cpp:677: undefined reference to example(k2c_tensor*, k2c_tensor*)'
/root/Bela/projects/MYPROJECT/render.cpp:678: undefined reference toexample(k2c_tensor, k2c_tensor)'
/root/Bela/projects/MYPROJECT/render.cpp:679: undefined reference to example(k2c_tensor*, k2c_tensor*)'
/root/Bela/projects/MYPROJECT/render.cpp:680: undefined reference toexample(k2c_tensor, k2c_tensor)

Which to me indicates some shortcoming in my approach where the compiler isn't getting the right links. I also explored using this approach: https://github.com/gosha20777/keras2cpp but the cmake version & c++17 version requirements weren't compatible and it seems like a longer journey than keras2c.

And finally, I've now noticed that if i just run rename my render.cpp to render.c all these problems go away, but then I can't seem to use things like AudioFile:

In file ./libraries/AudioFile/AudioFile.h: 'string' file not found column: 10, line: 2

Referenced posts:
https://forum.bela.io/d/629-problem-linking/2 --> really useful for command line interactions w/ bela. i tried the "first approach" without success.
https://forum.bela.io/d/2223-compiling-with-external-libraries/2 -> more insight to the make commands
https://forum.bela.io/d/2786-using-tflite-within-a-bela-project/3 -> tflite setup information

That was exactly it, worked like a charm!

Sadly trying to predict inside the render block seems to crash my program - it processes a sample in setup just fine

void render(BelaContext *context, void *userData)
{
    for(unsigned int n = 0; n < context->audioFrames; n++) {
        if(++gReadPointer > gSampleBuffer.size())
            gReadPointer = 0;
	float out = gSampleBuffer[gReadPointer];
	// iterate window
	for (int i = 0; i < 7; i++) {
	    model_in[i] = model_in[i+1];
	}
        model_in[7] = out;
	model(&model_in_tensor, &model_out_tensor);
	float pred = model_out[0];
        audioWrite(context, n, 0, pred);
        audioWrite(context, n, 1, pred);
    }
}

This code is using a model that takes in an array of 8 floats, returns 1 so I'm trying to process the audio as a sliding window and then run the inference method:

#include <Bela.h>
#include <vector>
#include <iostream>
#include <libraries/AudioFile/AudioFile.h>
#include "include/k2c_include.h" 
#include "models/model.h" 

std::string gFilename = "guitar.wav";
std::vector<float> gSampleBuffer;
int gReadPointer = 0;

// ml model
float model_in[8] = {0, 0, 0, 0, 0, 0, 0, 0,}; 
float model_out[1] = {0};
k2c_tensor model_in_tensor = {model_in,2,8,{8,1,1,1,1}};
k2c_tensor model_out_tensor = {model_out,1,1,{1,1,1,1,1}}; 

bool setup(BelaContext *context, void *userData)
{
	ml(&model_in_tensor, &model_out_tensor);
	std::cout << model_out[0] << std::endl;
	
	// load buffer
	gSampleBuffer = AudioFileUtilities::loadMono(gFilename);
	return true;
}

void render(BelaContext *context, void *userData)
{
    for(unsigned int n = 0; n < context->audioFrames; n++) {
        if(++gReadPointer > gSampleBuffer.size())
            gReadPointer = 0;

		float out = gSampleBuffer[gReadPointer];
		
		// iterate sliding window
		for (int i = 0; i < 7; i++) {
		    model_in[i] = model_in[i+1];
		}
		model_in[7] = out;

		model(&model_in_tensor, &model_out_tensor);
		
		float pred = model_out[0];

		audioWrite(context, n, 0, pred);
		audioWrite(context, n, 1, pred);
    }
}

Note: I wrapped the header files themselves with:

#ifdef __cplusplus
extern "C" {  
#endif 

The error is that it starts to run and then the audio crackles and then it shuts down:

Running project ...
-0.0113054
Bela has disconnected. Any changes you make will not be saved. Check your USB connection and reboot Bela.