Day: July 11, 2015

https://isocpp.org/wiki/faq/virtual-functions#pure-virtual

I removed almost all of my if and/or switch statements using pure virtual functions.

/* Sound.h */

#ifndef SOUND_H_
#define SOUND_H_

#include "AlsaParams.h"
#include <asoundlib.h>;

class Sound : public AlsaParams {
public:
	Sound();
	virtual int get_channels   () const = 0;
	virtual int get_nfft       () const = 0;
	virtual int get_spectrum_x () const = 0;
	virtual int get_spectrum_y () const = 0;
	virtual int get_waterfall_x() const = 0;
	virtual int get_waterfall_y() const = 0;
	virtual int asound_fftcopy () = 0;
	int asound_init();
	int asound_go();
	int asound_read();
	int asound_set_hwparams();
	int asound_set_swparams();
	virtual ~Sound();
private:
	int count = 0;
};

#endif /* SOUND_H_ */

/* SoundIC7410.h */

#ifndef SOUNDIC7410_H_
#define SOUNDIC7410_H_

#include "AlsaParams.h"
#include "Sound.h"

class SoundIC7410: public Sound {
public:
	SoundIC7410(char *s);
	int get_channels   () const override { return channels; }
	int get_nfft       () const override { return     nfft; }
	int get_spectrum_x () const override { return      512; }
	int get_spectrum_y () const override { return       50; }
	int get_waterfall_x() const override { return      512; }
	int get_waterfall_y() const override { return      150; }
	int asound_fftcopy() override;
	virtual ~SoundIC7410();
};

#endif /* SOUNDIC7410_H_ */

There is now only one such statement here:

void f(Sound *s){
	nch = s->get_channels();
	for(int ix=0;ix<spectrum_x;ix++) {
		if(nch == 1) { /* IC7410 */
			ixx = ix;
		} else if(nch == 2) { /* Soft66LC4 */
			ixx = (2*nfft - (spectrum_x/2) + ix) % nfft;
		}
		// draw spectrum and waterfall here
	}
}

The if statement is here because I wish to set the DC to the left edge or to the center depending on the signals. Of course, I can write functions for each derived class, like:
ixx= s->g(ix);
but, I do not know if I should.