NULL is OK, both for passing and for returning.
Parameter points to an array of items.
Generics and defining elements of containers and arrays.
Parameter for input and for returning results. Default is transfer full.
NULL must not be passed as the value in, out, in-out; or as a return value.
NULL may be passed as the value in, out, in-out; or as a return value.
Parameter for returning results. Default is transfer full.
Out parameter, where caller must allocate storage.
The callback is valid until first called.
Exposed in C code, not necessarily available in other languages.
The caller owns the data container, but not the data inside it.
The caller owns the data, and is responsible for free it.
The data is owned by the callee, which is responsible of freeing it.