The CUPS array API provides a high-performance generic array container.
The contents of the array container can be sorted and the container itself is
designed for optimal speed and memory usage under a wide variety of conditions.
Sorted arrays use a binary search algorithm from the last found or inserted
element to quickly find matching elements in the array. Arrays created with the
optional hash function can often find elements with a single lookup. The
cups_array_t type is used when
referring to a CUPS array.
The CUPS scheduler (cupsd) and many of the CUPS API functions use the array API to efficiently manage large lists of data.
Arrays are created using either the
cupsArrayNew,
cupsArrayNew2, or
cupsArrayNew3 functions. The
first function creates a new array with the specified callback function
and user data pointer:
#include <cups/array.h> static int compare_func(void *first, void *second, void *user_data); void *user_data; cups_array_t *array = cupsArrayNew(compare_func, user_data);
The comparison function (type
cups_arrayfunc_t) is called
whenever an element is added to the array and can be NULL to
create an unsorted array. The function returns -1 if the first element should
come before the second, 0 if the first and second elements should have the same
ordering, and 1 if the first element should come after the second.
The "user_data" pointer is passed to your comparison function. Pass
NULL if you do not need to associate the elements in your array
with additional information.
The cupsArrayNew2 function adds
two more arguments to support hashed lookups, which can potentially provide
instantaneous ("O(1)") lookups in your array:
#include <cups/array.h> #define HASH_SIZE 512 /* Size of hash table */ static int compare_func(void *first, void *second, void *user_data); static int hash_func(void *element, void *user_data); void *user_data; cups_array_t *hash_array = cupsArrayNew2(compare_func, user_data, hash_func, HASH_SIZE);
The hash function (type
cups_ahash_func_t) should return a
number from 0 to (hash_size-1) that (hopefully) uniquely identifies the
element and is called whenever you look up an element in the array with
cupsArrayFind. The hash size is
only limited by available memory, but generally should not be larger than
16384 to realize any performance improvement.
The cupsArrayNew3 function adds
copy and free callbacks to support basic memory management of elements:
#include <cups/array.h> #define HASH_SIZE 512 /* Size of hash table */ static int compare_func(void *first, void *second, void *user_data); static void *copy_func(void *element, void *user_data); static void free_func(void *element, void *user_data); static int hash_func(void *element, void *user_data); void *user_data; cups_array_t *array = cupsArrayNew3(compare_func, user_data, NULL, 0, copy_func, free_func); cups_array_t *hash_array = cupsArrayNew3(compare_func, user_data, hash_func, HASH_SIZE, copy_func, free_func);
Once you have created the array, you add elements using the
cupsArrayAdd
cupsArrayInsert functions.
The first function adds an element to the array, adding the new element
after any elements that have the same order, while the second inserts the
element before others with the same order. For unsorted arrays,
cupsArrayAdd appends the element to
the end of the array while
cupsArrayInsert inserts the
element at the beginning of the array. For example, the following code
creates a sorted array of character strings:
#include <cups/array.h> /* Use strcmp() to compare strings - it will ignore the user_data pointer */ cups_array_t *array = cupsArrayNew((cups_array_func_t)strcmp, NULL); /* Add four strings to the array */ cupsArrayAdd(array, "One Fish"); cupsArrayAdd(array, "Two Fish"); cupsArrayAdd(array, "Red Fish"); cupsArrayAdd(array, "Blue Fish");
Elements are removed using the
cupsArrayRemove function, for
example:
#include <cups/array.h> /* Use strcmp() to compare strings - it will ignore the user_data pointer */ cups_array_t *array = cupsArrayNew((cups_array_func_t)strcmp, NULL); /* Add four strings to the array */ cupsArrayAdd(array, "One Fish"); cupsArrayAdd(array, "Two Fish"); cupsArrayAdd(array, "Red Fish"); cupsArrayAdd(array, "Blue Fish"); /* Remove "Red Fish" */ cupsArrayRemove(array, "Red Fish");
Finally, you free the memory used by the array using the
cupsArrayDelete function. All
of the memory for the array and hash table (if any) is freed, however CUPS
does not free the elements unless you provide copy and free functions.
CUPS provides several functions to find and enumerate elements in an array. Each one sets or updates a "current index" into the array, such that future lookups will start where the last one left off:
cupsArrayFindcupsArrayFirstcupsArrayIndexcupsArrayLastcupsArrayNextcupsArrayPrevEach of these functions returns NULL when there is no
corresponding element. For example, a simple for loop using the
cupsArrayFirst and
cupsArrayNext functions will
enumerate all of the strings in our previous example:
#include <cups/array.h> /* Use strcmp() to compare strings - it will ignore the user_data pointer */ cups_array_t *array = cupsArrayNew((cups_array_func_t)strcmp, NULL); /* Add four strings to the array */ cupsArrayAdd(array, "One Fish"); cupsArrayAdd(array, "Two Fish"); cupsArrayAdd(array, "Red Fish"); cupsArrayAdd(array, "Blue Fish"); /* Show all of the strings in the array */ char *s; for (s = (char *)cupsArrayFirst(array); s != NULL; s = (char *)cupsArrayNext(array)) puts(s);