void* array_allocate(array* x, uint64 membersize, int64 pos);
t* p = array_allocate(&x,sizeof(t),pos);
array_allocate makes sure that enough bytes are allocated in x for
at least pos+1 objects of type t. (The size of t must
be positive; otherwise the effects are undefined.) If not enough bytes
are allocated (or x is unallocated), array_allocate allocates more
bytes, moving the dynamically allocated region if necessary.
array_allocate often allocates somewhat more bytes than necessary, to
save time later.
array_allocate then makes sure that the number of bytes initialized
covers at least those pos+1 objects. If not enough bytes are
initialized, array_allocate initializes more bytes (setting them to 0),
up to exactly the end of the pos+1st object.
array_allocate then returns a pointer to the pos+1st object; i.e.,
object number pos, with objects numbered starting at 0. This
pointer can be used to change or inspect the object. The pointer can
continue to be used through subsequent calls to array_get, array_start,
array_length, and array_bytes, but it must not be used after any other
operations on this array.
If something goes wrong, array_allocate returns 0, setting errno
appropriately, without touching x. In particular, array_allocate
returns 0 if
x has failed, or
pos is negative, or
not enough memory is available.
array_allocate does not change x to have failed; if you want
to do that, use array_fail.