Linker error

ryjobil

I'm scratching my head...partly because the build and linking process is still a mystery to me 🙂

Here is the shortest I can cut down the problem, and maybe somebody can point me toward the kinds of things I should be doing to get it to work. It might be that I should wrap the code up into a class or something, but this really should work if I have the correct compiler flags:

External file, flange.h:

 typedef struct tflanger_t {
.
.
.
} tflanger;

.
.
. 
     tflanger* tflanger_init (tflanger*, float, float); //provide maximum delay time and the sample rate
     void tflanger_tick(tflanger*, int , float*);  //main processing routine. Returns output in the same buffer 
.
.
.

Then render.cpp:

void render(BelaContext *context, void *userData)
{
	format_audio_buffer(context, samples, 0);	
	tflanger_tick(delayline, nframes, samples);
	for(unsigned int n = 0; n < context->audioFrames; n++) {
		audioWrite(context, n, 0, samples[n]);
		audioWrite(context, n, 1, samples[n]);
	}	
}

Everything compiles successfully, but linker fails:

/root/Bela/projects/MultiDelay/build/render.o: In function `render(BelaContext*, void*)':
/root/Bela/projects/MultiDelay/render.cpp:(.text+0xd0): undefined reference to `tflanger_tick(tflanger_t*, int, float*)'

In the project build directory are all of the *.o files I would expect to see but perhaps the linker is not looking here?

Any help appreciated. Thanks.

giuliomoro

When you get a linker error the culprit is most likely in your C\C++ source files, not (or not only) in your Header files. what does your source file look like? If it is a .c file, then either rename it to .cpp or you need to add extern "C" in your .h file.

ryjobil

It's magic! 😉
Thanks. You had given me the answer in a different post, but I didn't connect 2 and 2 about linking when compilation had been successful.
Thank you.

giuliomoro

This is a good page about mixing C and C++:
https://isocpp.org/wiki/faq/mixing-c-and-cpp

ryjobil

Thanks, that's a good reference. I agree with this:

"BTW there is another way to handle this whole thing: compile all your code (even your C-style code) 
using a C++ compiler. That pretty much eliminates the need to mix C and C++, plus it will cause you to
 be more careful (and possibly —hopefully!— discover some bugs) in your C-style code. 
 ... basically because the C++ compiler is more careful/picky than your C compiler. The point is that 
the effort required to clean up your C-style code may be less than the effort required to mix C and C++,
 and as a bonus you get cleaned up C-style code."

Fortunately my code was written in a C++ friendly manner, so there was only a minor tweak to make it compile as a .cpp. My missing key to Bela build system is it would make an attempt to compile C files with a C compiler instead of attempting to compile everything c-like with C++ compiler (probably I would discover this if I were to give closer examination into the Makefile).

Anyway, this experiment shows me I can code in the style that is most comfortable to me and it will work fine on Bela as long as I use the filename extension ".cpp". Now there is a nice lush chorus effect coming out of my Bela.

After hearing the effect of this code through my Raspberry Pi and Behringer USB dongle I am struck by the increased audio quality of Bela.