yes, I remember the compilation fails on Visual Studio if your dll is loaded by an application so if Pd is running a patch with your external you can't compile before closing Pd.

You still don't use the realloc method properly. The method is for reallocation, so you should give it the pointer to the memory you want to resize.
Something like

temp_vector = realloc(x->vector, len_avg_new * x->block_size * sizeof(t_sample*));
if (temp_vector) {
   // allocation succeed
   x->vector = temp_vector;
}
else
{
    // allocation failed but x->vector isn't freed so you have the choice, 
    // you can free it or continue to use the memory allocated.
   free(x->vector);
   x->vector = NULL;
}

With the first, x->vector should be set to NULL, this way the method will acts like malloc. In your code, you allocate new memory each time you resize the arrays without releasing them thus you have a lot of memory leaks.

Small esthetic remark: you can remove x_in and x_out in your object's structure, you never use it (and use directly outlet_new(&x->x_obj, &s_signal); without x->x_out = before).

@Pierre-Guillot said:

You still don't use the realloc method properly. The method is for reallocation, so you should give it the pointer to the memory you want to resize.
In your code, you allocate new memory each time you resize the arrays without releasing them thus you have a lot of memory leaks.

Sorry, I can't see my error. I think, lines 116-119 do free the allocated memory:

if (x->matrix) free(x->matrix);
    if (x->vector) free(x->vector);
    x->vector = temp_vector;
    x->matrix = temp_matrix;

VS shows me the process memory. When I do produce memory leaks, the process memory should raise, I guess. But with my code it corresponds to the size of the matrix. So lowering the sample length lowers the memory also.

With the first, x->vector should be set to NULL, this way the method will acts like malloc.

OK. I added x->matrix = NULL; x->vector = NULL; to the method average_init_arrays

My updated code is here:
https://github.com/XRoemer/puredata/blob/master/average%7E/C/r_average%7E2.h
(I also changed the method average_resize_arrays from:

void average_resize_arrays(t_average_tilde *x, t_floatarg f) {

    x->row = 0;
    x->len_avg = f;

    average_resize_avg(x, f);
    average_resize_matrix(x, f);

    if (!x->avg && !x->matrix) {
        x->matrix = NULL;
        pd_error(x, "allocation failed");
    }
}

to:

void average_resize_arrays(t_average_tilde *x, t_floatarg f) {

    x->row = 0;
    x->len_avg = f;

    average_resize_avg(x, f);
    average_resize_matrix(x, f);

    if (!x->avg || !x->matrix) {
        if (x->matrix) free(x->matrix);
        if (x->vector) free(x->vector);
        x->matrix = NULL;
        x->vector = NULL;
        pd_error(x, "allocation failed");
    }
}

Sorry, I can't see my error. I think, lines 116-119 do free the allocated memory:

Sorry I didn't notice these lines but you still use realloc like malloc (you never reallocate memory, you only allocate because the pointer you give to the function is always null), so you should change all the function with malloc, for example:

temp_vector = realloc(temp_vector, len_avg_new * x->block_size * sizeof(t_sample*));

by

temp_vector = malloc(len_avg_new * x->block_size * sizeof(t_sample*));

I see - I corrected the code.

Again, thanks a lot for your help.