.TH array_allocate 3
.SH NAME
array_allocate \- make sure array has at least n elements allocated
.SH SYNTAX
.B #include <libowfat/array.h>

void* \fBarray_allocate\fP(array* \fIx\fR, uint64 \fImembersize\fR, int64 \fIpos\fR);

  array \fIx\fR;
  int64 \fIpos\fR;
  \fIt\fR* p = array_allocate(&\fIx\fR,sizeof(\fIt\fR),\fIpos\fR);

.SH DESCRIPTION
array_allocate makes sure that enough bytes are allocated in \fIx\fR for
at least \fIpos\fR+1 objects of type \fIt\fR. (The size of \fIt\fR must
be positive; otherwise the effects are undefined.) If not enough bytes
are allocated (or \fIx\fR 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 \fIpos\fR+1 objects. If not enough bytes are
initialized, array_allocate initializes more bytes (setting them to 0),
up to exactly the end of the \fIpos\fR+1st object.

array_allocate then returns a pointer to the \fIpos\fR+1st object; i.e.,
object number \fIpos\fR, 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 \fBerrno\fR
appropriately, without touching \fIx\fR. In particular, array_allocate
returns 0 if

.sp 1
.IP \(bu
\fIx\fR has failed, or
.IP \(bu
\fIpos\fR is negative, or
.IP \(bu
not enough memory is available.
.PP

array_allocate does \fInot\fR change \fIx\fR to have failed; if you want
to do that, use array_fail.

.SH PERFORMANCE
This function can call realloc when the array needs to be enlarged.
Under exceptional circumstances, this can lead to blocking the current thread.
It will also zero-fill the newly enlarged part of the array, leading to
all pages being mapped in by the operating system.  If a small array is
enlarged to a very large array, this can lead to swapping and blocking.
.SH "SEE ALSO"
array_get(3), array_start(3), array_fail(3)