[vorbis-dev] Re: vorbisfile updates, and a couple of questions

[Greg Stark]

Jonathan Blow <jon at bolt-action.com> writes:

> > Casting function pointers appears
> > to be a rather arcane sort of thing to do. Anyone with more C clues than I
> > care to speak up?
> 
> The syntax for that has got to be hairy... what I would do is make typedefs
> for both types, and then cast one to the other.  So...

You might be better off keeping this simpler:

typedef int (*vorbis_callback)(void *closure, vorbis_op *op);

int my_read_callback(void *closure, vorbis_op *op) {
  FILE *input = (FILE*)closure;
  assert(op->operation == VORBIS_READ);
  ...
}

int my_write_callback(void *closure, vorbis_op *op) {
...

This means you can't just pass fread et al as callbacks, but it avoids having
hairy casts and different callbacks depending on whether the closure is a
FILE* or an opaque object. It does have one major disadvantage, you can't add
stuff to the vorbis_op structure without invalidating old code, which is
annoying.


-- 
greg

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