Re: Advice on how to return a list of values

The usual method goes like this:

The caller p***** a pointer to storage that it provides, and the size
of available storage. The called function provides the data, and
returns how much data is available. If the pointer passed in is a null
pointer then the callee just provides the amount of data available,
without calling anything. If the pointer passed is not null, but the
size is not enough then the callee doesn't write more data than
storage available.

That makes it quite clear what the callee has to do. For the caller,
there are two strategies: If you know an amount of data that is
usually enough, then do a call with a limited amount of local data
first; if this fails then the caller will know how much storage is
needed and will malloc it. Alternatively, if there is no reasonable
guess about the data size, pass a null pointer in the first call, then
make a second call with the storage properly allocated.