Michael Niedermayer: > On Mon, May 04, 2020 at 08:22:50PM +0200, Andreas Rheinhardt wrote: >> Allocating an array with zero entries is both unnecessary as well as >> potentially troublesome because the behaviour in this case is not really >> well defined. > > What is not well defined ? > The behaviour of our memory-allocation functions in case one requests to allocate zero bytes is not well-defined (does it return NULL or not?). E.g. although the documentation of av_mallocz_array() (which applies to av_calloc, too) treats the size and nmemb parameters symmetrically, the actual implementation differed until commit b7d9507bb8c4d1b8bf99158d6859a5b2ecd73298 (up until then, a size of zero would have resulted in NULL being returned). In the discussion [1] around this patch there were devs favouring returning NULL upon any request to allocate zero bytes. The NUT muxer is btw one of the two main reasons for failing fate-tests in case one returned NULL when an allocation of zero bytes is requested.
What happens on allocation of zero bytes is implementation-defined for the analogous C functions; in our implementation the only function that explicitly documents what happens when the size fed to it is zero is av_realloc() which does not abide by its documentation (it does not free anything when size is zero, but rather reallocates the buffer to a size of one). - Andreas [1]: https://ffmpeg.org/pipermail/ffmpeg-devel/2020-April/260493.html _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
