.Dd $Mdocdate: November 24 2022 $
.Dt ARRAY 3
.Os Telodendria Project
.Sh NAME
.Nm Array
.Nd A simple dynamic array data structure.
.Sh SYNOPSIS
.In Array.h
.Ft Array *
.Fn ArrayCreate "void"
.Ft void
.Fn ArrayFree "Array *"
.Ft int
.Fn ArrayTrim "Array *"
.Ft size_t
.Fn ArraySize "Array *"
.Ft void *
.Fn ArrayGet "Array *" "size_t"
.Ft int
.Fn ArrayInsert "Array *" "void *" "size_t"
.Ft int
.Fn ArrayAdd "Array *" "void *"
.Ft void *
.Fn ArrayDelete "Array *" "size_t"
.Ft void
.Fn ArraySort "Array *" "int (*) (void *, void *)"
.Ft Array *
.Fn ArrayFromVarArgs "size_t" "va_list"
.Ft Array *
.Fn ArrayDuplicate "Array *"
.Sh DESCRIPTION
These functions implement a simple array data structure that
is automatically resized as necessary when new values are added.
This implementation does not actually store the values of the
items in it; it only stores pointers to the data. As such, you will
still have to manually maintain all your data. The advantage of this
is that these functions don't have to copy data, and thus don't care
how big the data is. Furthermore, arbitrary data can be stored in the
array.
.Pp
This array implementation is optimized for storage space and appending.
Deletions are expensive in that all the items of the list above a deletion
are moved down to fill the hole where the deletion occurred. Insertions are
also expensive in that all the elements above the given index must be shifted
up to make room for the new element.
.Pp
Due to these design choices, this array implementation is best suited to
linear writing, and then linear or random reading.
.Pp
These functions operate on an array structure which is opaque to the
caller.
.Pp
.Fn ArrayCreate
and
.Fn ArrayFree
allocate and deallocate an array, respectively.
Note that
.Fn ArrayFree
does not free any of the values stored in the array; it is the caller's
job to manage the memory for each item. Typically, the caller would
iterate over all the items in the array and free them before freeing
the array.
.Fn ArrayTrim
reduces the amount of unused memory by calling
.Xr realloc 3
on the internal structure to perfectly fit the elements in the array. It
is intended to be used by functions that return relatively read-only arrays
that will be long-lived.
.Pp
.Fn ArrayInsert
and
.Fn ArrayDelete
are the main functions used to modify the array.
.Fn ArrayAdd
is a convenience method that simply appends a value to the end of the
array. It uses
.Fn ArrayInsert .
The array can also be sorted by using
.Fn ArraySort ,
which takes a pointer to a function that compares elements. The function
should take two
.Dv void
pointers as parameters, and return an integer. The return value indicates
to the algorithm how the elements relate to each other. A return value of
0 indicates the elements are identical. A return value greater than 0
indicates that the first item is "bigger" than the second item and should
thus appear after it in the array, and a value less than zero indicates
the opposite: the second element should appear after the first in the array.
.Pp
.Fn ArrayGet
is used to get the element at the specified index.
.Pp
.Fn ArrayFromVarArgs
is used to convert a variadic arguments list into an Array. In many
cases, the Array API is much easier to work with than
.Fn va_arg
and friends.
.Pp
.Fn ArrayDuplicate
duplicates an existing array. Note that Arrays only hold
pointers to data, not the data itself, so the duplicated array will
point to the same places in memory as the original array.
.Sh RETURN VALUES
.Fn ArrayCreate ,
.Fn ArrayFromVarArgs ,
and
.Fn ArrayDuplicate
return a pointer on the heap to a newly allocated array structure, or
.Dv NULL
if the allocation fails.
.Pp
.Fn ArrayGet
and
.Fn ArrayDelete
return pointers to values that were put into the array, or
.Dv NULL
if the provided array is
.Dv NULL
or the provided index was out of bounds.
.Fn ArrayDelete
returns the element at the specified index after removing it so that
it can be properly handled by the caller.
.Pp
.Fn ArrayTrim ,
.Fn ArrayInsert ,
and
.Fn ArrayAdd
return a boolean value indicating their status. They return a value of zero
on failure, and a non-zero value on success.
.Sh SEE ALSO
.Xr HashMap 3 ,
.Xr Queue 3