array_allocate(3)

NAME
array_allocate - make sure array has at least n elements allocated

SYNTAX
#include <libowfat/array.h>

void* array_allocate(array* x, uint64 membersize, int64 pos);

  array x;
  int64 pos;
  t* p = array_allocate(&x,sizeof(t),pos);

DESCRIPTION
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.

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.

SEE ALSO
array_get(3), array_start(3), array_fail(3)