Generating two sines using PortAudio

pa-sine.c

#include "portaudio.h"
#include <stdio.h>
#include <stdlib.h>

typedef int PaStreamCallback( const void *input,
    void *output,
    unsigned long frameCount,
    const PaStreamCallbackTimeInfo* timeInfo,
    PaStreamCallbackFlags statusFlags,
    void *userData ) ;

typedef struct
{
    float left_phase;
    float right_phase;
}   
paTestData;
/* This routine will be called by the PortAudio engine when audio is needed.
   It may called at interrupt level on some machines so don't do anything
   that could mess up the system like calling malloc() or free().
*/ 
static int patestCallback( const void *inputBuffer, void *outputBuffer,
                           unsigned long framesPerBuffer,
                           const PaStreamCallbackTimeInfo* timeInfo,
                           PaStreamCallbackFlags statusFlags,
                           void *userData )
{
    /* Cast data passed through stream to our structure. */
    paTestData *data = (paTestData*)userData; 
    float *out = (float*)outputBuffer;
    unsigned int i;
    (void) inputBuffer; /* Prevent unused variable warning. */
    
    for( i=0; i<framesPerBuffer; i++ )
    {
        *out++ = data->left_phase;  /* left */
        *out++ = data->right_phase;  /* right */
        /* Generate simple sawtooth phaser that ranges between -1.0 and 1.0. */
        data->left_phase += 0.03f;
        /* When signal reaches top, drop back down. */
        if( data->left_phase >= 1.0f ) data->left_phase -= 2.0f;
        /* higher pitch so we can distinguish left and right. */
        data->right_phase += 0.05f;
        if( data->right_phase >= 1.0f ) data->right_phase -= 2.0f;
    }
    return 0;
}

#define SAMPLE_RATE (44100)
static paTestData data;

int main (int argc, char *argv) {
  PaStream *stream;
  PaError err;

  err = Pa_Initialize();
  if( err != paNoError ) {
    puts("Failed to initialize PortAudio");
    exit(1);
  }

  /* Open an audio I/O stream. */
  err = Pa_OpenDefaultStream( &stream,
      0,          /* no input channels */
      2,          /* stereo output */
      paFloat32,  /* 32 bit floating point output */
      SAMPLE_RATE,
      256,        /* frames per buffer, i.e. the number
                     of sample frames that PortAudio will
                     request from the callback. Many apps
                     may want to use
                     paFramesPerBufferUnspecified, which
                     tells PortAudio to pick the best,
                     possibly changing, buffer size.*/
      patestCallback, /* this is your callback function */
      &data ); /*This is a pointer that will be passed to
                 your callback*/
  if( err != paNoError ) {
    puts("Failed to open a stream");
    exit(1);
  }

  err = Pa_StartStream( stream );
  if( err != paNoError ) {
    puts("Failed to start a stream");
    exit(1);
  }

  /* Sleep for several seconds. */
  Pa_Sleep(3 * 1000);

  err = Pa_StopStream( stream );
  if( err != paNoError ) {
    puts("Failed to stop a stream");
    exit(1);
  }

  err = Pa_CloseStream( stream );
  if( err != paNoError ) {
    puts("Failed to close a stream");
    exit(1);
  }

  err = Pa_Terminate();
  if( err != paNoError ) {
    puts("Failed to terminate PortAudio");
    exit(1);
  }
}

static functions were something I ignored, thanks. http://www.gnu.org/software/gnu-c-manual/gnu-c-manual.html#Static-Functions

@greut It's good practice to hide everything that you don't want to expose, when writing a library.

When writing a program, pretty much every function should be static - except main of course, because the entry point needs to be visible for the linker (it is called by C runtime libraries shipped with your OS - the actual entry point of the program, _start, is generated by the C compiler itself.)

I'd love to write an asm course at some point :)

Note that most of the code here it copy-pasted/adapted from the PortAudio tutorial that can be found here: http://portaudio.com/docs/v19-doxydocs/tutorial_start.html