Simple sine wave synthesizer

main.cpp

#include <iostream>
#include <SDL2/SDL.h>
#include "oscsine.h"

float freq = 440.f; //A4
int samplerate = 44100;
OscSine sine(0.5, freq, samplerate);

void generate(void* userdata, Uint8* stream, int len) {
	float *streamf = (float*) stream; //SDL gives uint8, convert to float
	for (int i=0; i<len/sizeof(float); i++) {
		streamf[i] = sine.advance(); //Index out of bounds causes a segfault
	}
};

int main() {
	if (SDL_InitSubSystem(SDL_INIT_AUDIO) < 0) return 1;
	
	SDL_AudioSpec spec;
	
	spec.freq = samplerate;
	spec.format = AUDIO_F32SYS;
	spec.channels = 1;
	spec.samples = 512;
	spec.callback = generate;
	
	auto audio = SDL_OpenAudioDevice(nullptr, 0, &spec, &spec, 0);
	if (audio < 0) std::cerr << "Error: " << SDL_GetError();
	SDL_PauseAudioDevice(audio, 0);
	SDL_Delay(4000);
	return 0;
	
}

oscsine.cpp

#include <iostream>
#include <math.h>
#include "oscsine.h"

OscSine::OscSine(float a, float f, int sr) : amp(a), freq(f), samplerate(sr)
{
    std::cout << "Sine freq " << freq << "\n";
}

float OscSine::advance()
{
    if (amp == 0) return 0.f; //Don't waste computational power if you can't hear it
    float wave = amp*sin(freq*2*3.1415926*time);
    time+=1.f/(double)samplerate;
    return wave;
}

oscsine.h

#ifndef OSCSINE_H
#define OSCSINE_H

class OscSine
{
public:
    OscSine(float a, float f, int sr);
    float amp;
    float freq;
	int samplerate;
    
    float advance();
private:
    double time;
};

#endif // OSCSINE_H