accessing buffer~

hi everybody,
first of all i'm a newbie in programming and i'm writing this external as the final project for my thesis at university.

i'm trying to access a buffer and copy all the values in an array of doubles,
but max crashes everytime i try to access the buffer.

these are the methods i'm trying to write

void fftesi_bang(t_fftesi *x)
{
    post("bang received, provo a leggere il buffer");
    t_buffer *buf = x->l_buf;
    copio_campioni(buf);
}

void copio_campioni(t_buffer *b)
{
    //float *tab;
    long i, chan;
    //double current_samp = 0.0;
    ATOMIC_INCREMENT((int32_t*)&b->b_inuse);
    post("speriamo bene");
    i = 1; chan = 1;
    if (!b->b_valid) {
        ATOMIC_DECREMENT(&b->b_inuse);
        return;
    }
    /*
    //copio il valore corrente in un array di dimensione 4096
    tab = b->b_samples;
    chan = 0; //usiamo solo il canale left
    for(i=0; ib_frames; i++)
    {
        segnale[i] = tab[i];
        post ("letto campioni");
    }
     */
    ATOMIC_DECREMENT((int32_t*)&b->b_inuse);
    return;
}

the zip file contains the dir placed in MaxSDK-5.1.6/examples/ with my xcode project.

thanks to all