Thu, 23 May 2024 20:29:28 +0200
fix members inherited by macro or include are not documented
1 ---
2 title: UCX Features
3 ---
5 <div id="modules">
7 ------------------------ ------------------------- ------------------- ---------------------------------
8 [Allocator](#allocator) [String](#string) [Buffer](#buffer) [Memory Pool](#memory-pool)
9 [Iterator](#iterator) [Collection](#collection) [List](#list) [Map](#map)
10 [Utilities](#utilities)
11 ------------------------ ------------------------- ------------------- ---------------------------------
13 </div>
15 ## Allocator
17 *Header file:* [allocator.h](api/allocator_8h.html)
19 The UCX allocator provides an interface for implementing an own memory allocation mechanism.
20 Various function in UCX provide an additional alternative signature that takes an allocator as
21 argument. A default allocator implementation using the stdlib memory management functions is
22 available via the global symbol `cxDefaultAllocator`.
24 If you want to define your own allocator, you need to initialize the `CxAllocator` structure
25 with a pointer to an allocator class (containing function pointers for the memory management
26 functions) and an optional pointer to an arbitrary memory region that can be used to store
27 state information for the allocator. An example is shown below:
29 ```c
30 struct my_allocator_state {
31 size_t total;
32 size_t avail;
33 char mem[];
34 };
36 static cx_allocator_class my_allocator_class = {
37 my_malloc_impl,
38 my_realloc_impl, // all these functions are somewhere defined
39 my_calloc_impl,
40 my_free_impl
41 };
43 CxAllocator create_my_allocator(size_t n) {
44 CxAllocator alloc;
45 alloc.cl = &my_allocator_class;
46 alloc.data = calloc(1, sizeof(struct my_allocator_state) + n);
47 return alloc;
48 }
49 ```
51 ## String
53 *Header file:* [string.h](api/string_8h.html)
55 UCX strings come in two variants: immutable (`cxstring`) and mutable (`cxmutstr`).
56 The functions of UCX are designed to work with immutable strings by default but in situations where it is necessary,
57 the API also provides alternative functions that work directly with mutable strings.
58 Functions that change a string in-place are, of course, only accepting mutable strings.
60 When you are using UCX functions, or defining your own functions, you are sometimes facing the "problem",
61 that the function only accepts arguments of type `cxstring` but you only have a `cxmutstr` at hand.
62 In this case you _should not_ introduce a wrapper function that accepts the `cxmutstr`,
63 but instead you should use the `cx_strcast()` function to cast the argument to the correct type.
65 In general, UCX strings are **not** necessarily zero-terminated. If a function guarantees to return zero-terminated
66 string, it is explicitly mentioned in the documentation of the respective function.
67 As a rule of thumb, you _should not_ pass the strings of a UCX string structure to another API without explicitly
68 ensuring that the string is zero-terminated.
70 ## Buffer
72 *Header file:* [buffer.h](api/buffer_8h.html)
74 Instances of this buffer implementation can be used to read from or write to memory like you would do with a stream.
75 This allows the use of `cx_stream_copy()` (see [Utilities](#utilities)) to copy contents from one buffer to another,
76 or from a file or network streams to the buffer and vice-versa.
78 More features for convenient use of the buffer can be enabled, like automatic memory management and automatic
79 resizing of the buffer space.
81 Since UCX 3.0, the buffer also supports automatic flushing of contents to another stream (or buffer) as an alternative
82 to automatically resizing the buffer space.
83 Please refer to the API doc for the fields prefixed with `flush_` to learn more.
85 ## Memory Pool
87 *Header file:* [mempool.h](api/mempool_8h.html)
89 A memory pool is providing an allocator implementation that automatically deallocates the memory upon its destruction.
90 It also allows you to register destructor functions for the allocated memory, which are automatically called before
91 the memory is deallocated.
92 Additionally, you may also register _independent_ destructor functions within a pool in case some external library
93 allocated memory for you, which should be destroyed together with this pool.
95 Many UCX features support the use of an allocator.
96 The [strings](#string), for instance, provide several functions suffixed with `_a` that allow specifying an allocator.
97 You can use this to keep track of the memory occupied by dynamically allocated strings and cleanup everything with
98 just a single call to `cxMempoolDestroy()`.
100 The following code illustrates this on the example of reading a CSV file into memory.
101 ```C
102 #include <stdio.h>
103 #include <cx/mempool.h>
104 #include <cx/linked_list.h>
105 #include <cx/string.h>
106 #include <cx/buffer.h>
107 #include <cx/utils.h>
109 typedef struct {
110 cxstring column_a;
111 cxstring column_b;
112 cxstring column_c;
113 } CSVData;
115 int main(void) {
116 CxMempool* pool = cxBasicMempoolCreate(128);
118 FILE *f = fopen("test.csv", "r");
119 if (!f) {
120 perror("Cannot open file");
121 return 1;
122 }
123 // close the file automatically at pool destruction
124 cxMempoolRegister(pool, f, (cx_destructor_func) fclose);
126 // create a buffer using the memory pool for destruction
127 CxBuffer *content = cxBufferCreate(NULL, 256, pool->allocator, CX_BUFFER_AUTO_EXTEND);
129 // read the file into the buffer and turn it into a string
130 cx_stream_copy(f, content, (cx_read_func) fread, (cx_write_func) cxBufferWrite);
131 fclose(f);
132 cxstring contentstr = cx_strn(content->space, content->size);
134 // split the string into lines - use the mempool for allocating the target array
135 cxstring* lines;
136 size_t lc = cx_strsplit_a(pool->allocator, contentstr,
137 CX_STR("\n"), SIZE_MAX, &lines);
139 // skip the header and parse the remaining data into a linked list
140 // the nodes of the linked list shall also be allocated by the mempool
141 CxList* datalist = cxLinkedListCreate(pool->allocator, NULL, sizeof(CSVData));
142 for (size_t i = 1 ; i < lc ; i++) {
143 if (lines[i].length == 0) continue;
144 cxstring fields[3];
145 size_t fc = cx_strsplit(lines[i], CX_STR(";"), 3, fields);
146 if (fc != 3) {
147 fprintf(stderr, "Syntax error in line %zu.\n", i);
148 cxMempoolDestroy(pool);
149 return 1;
150 }
151 CSVData data;
152 data.column_a = fields[0];
153 data.column_b = fields[1];
154 data.column_c = fields[2];
155 cxListAdd(datalist, &data);
156 }
158 // iterate through the list and output the data
159 CxIterator iter = cxListIterator(datalist);
160 cx_foreach(CSVData*, data, iter) {
161 printf("Column A: %.*s | "
162 "Column B: %.*s | "
163 "Column C: %.*s\n",
164 (int)data->column_a.length, data->column_a.ptr,
165 (int)data->column_b.length, data->column_b.ptr,
166 (int)data->column_c.length, data->column_c.ptr
167 );
168 }
170 // cleanup everything, no manual free() needed
171 cxMempoolDestroy(pool);
173 return 0;
174 }
175 ```
177 ## Iterator
179 *Header file:* [iterator.h](api/iterator_8h.html)
181 In UCX 3 a new feature has been introduced to write own iterators, that work with the `cx_foreach` macro.
182 In previous UCX releases there were different hard-coded foreach macros for lists and maps that were not customizable.
183 Now, creating an iterator is as simple as creating a `CxIterator` struct and setting the fields in a meaningful way.
185 You do not always need all fields in the iterator structure, depending on your use case.
186 Sometimes you only need the `index` (for example when iterating over simple lists), and other times you will need the
187 `slot` and `kv_data` fields (for example when iterating over maps).
189 If the predefined fields are insufficient for your use case, you can alternatively create your own iterator structure
190 and place the `CX_ITERATOR_BASE` macro as first member of that structure.
192 Usually an iterator is not mutating the collection it is iterating over.
193 In some programming languages it is even disallowed to change the collection while iterating with foreach.
194 But sometimes it is desirable to remove an element from the collection while iterating over it.
195 For this purpose, most collections allow the creation of a _mutating_ iterator.
196 The only differences are, that the `mutating` flag is `true` and the `src_handle` is not const.
197 On mutating iterators it is allowed to call the `cxFlagForRemoval()` function, which instructs the iterator to remove
198 the current element from the collection on the next call to `cxIteratorNext()` and clear the flag afterward.
199 If you are implementing your own iterator, it is up to you to implement this behavior.
201 ## Collection
203 *Header file:* [collection.h](api/collection_8h.html)
205 Collections in UCX 3 have several common features.
206 If you want to implement an own collection data type that uses the same features, you can use the
207 `CX_COLLECTION_BASE` macro at the beginning of your struct to roll out all members a usual UCX collection has.
208 ```c
209 struct my_fancy_collection_s {
210 CX_COLLECTION_BASE;
211 struct my_collection_data_s *data;
212 };
213 ```
214 Based on this structure, this header provides some convenience macros for invoking the destructor functions
215 that are part of the basic collection members.
216 The idea of having destructor functions within a collection is that you can destroy the collection _and_ the
217 contents with one single function call.
218 When you are implementing a collection, you are responsible for invoking the destructors at the right places, e.g.
219 when removing (and deleting) elements in the collection, clearing the collection, or - the most prominent case -
220 destroying the collection.
222 You can always look at the UCX list and map implementations if you need some inspiration.
224 ## List
226 *Header file:* [list.h](api/list_8h.html)
228 This header defines a common interface for all list implementations.
230 UCX already comes with two common list implementations (linked list and array list) that should cover most use cases.
231 But if you feel the need to implement an own list, the only thing you need to do is to define a struct with a
232 `struct cx_list_s` as first member, and set an appropriate list class that implements the functionality.
233 It is strongly recommended that this class is shared among all instances of the same list type, because otherwise
234 the `cxListCompare` function cannot use the optimized implementation of your class and will instead fall back to
235 using iterators to compare the contents element-wise.
237 ### Linked List
239 *Header file:* [linked_list.h](api/linked__list_8h.html)
241 On top of implementing the list interface, this header also defines several low-level functions that
242 work with arbitrary structures.
243 Low-level functions, in contrast to the high-level list interface, can easily be recognized by their snake-casing.
244 The function `cx_linked_list_at`, for example, implements a similar functionality like `cxListAt`, but operates
245 on arbitrary structures.
246 The following snippet shows how it is used.
247 All other low-level functions work similarly.
248 ```c
249 struct node {
250 node *next;
251 node *prev;
252 int data;
253 };
255 const ptrdiff_t loc_prev = offsetof(struct node, prev);
256 const ptrdiff_t loc_next = offsetof(struct node, next);
257 const ptrdiff_t loc_data = offsetof(struct node, data);
259 struct node a = {0}, b = {0}, c = {0}, d = {0};
260 cx_linked_list_link(&a, &b, loc_prev, loc_next);
261 cx_linked_list_link(&b, &c, loc_prev, loc_next);
262 cx_linked_list_link(&c, &d, loc_prev, loc_next);
264 cx_linked_list_at(&a, 0, loc_next, 2); // returns pointer to c
265 ```
267 ### Array List
269 *Header file:* [array_list.h](api/array__list_8h.html)
271 Since low-level array lists are just plain arrays, there is no need for such many low-level functions as for linked
272 lists.
273 However, there is one extremely powerful function that can be used for several complex tasks: `cx_array_copy`.
274 The full signature is shown below:
275 ```c
276 enum cx_array_result cx_array_copy(
277 void **target,
278 size_t *size,
279 size_t *capacity, // optional
280 size_t index,
281 void const *src,
282 size_t elem_size,
283 size_t elem_count,
284 struct cx_array_reallocator_s *reallocator // optional
285 );
286 ```
287 The `target` argument is a pointer to the target array pointer.
288 The reason for this additional indirection is that - given that you provide a `reallocator` - this function writes
289 back the pointer to the possibly reallocated array.
290 The next two arguments are pointers to the `size` and `capacity` of the target array.
291 Tracking the capacity is optional.
292 If you do not specify a pointer for the capacity, automatic reallocation of the array is entirely disabled (i.e. it
293 does not make sense to specify a `reallocator` then).
294 In this case, the function cannot copy more than `size-index` elements and if you try, it will return
295 `CX_ARRAY_REALLOC_NOT_SUPPORTED` and do nothing.
297 On a successful invocation, the function copies `elem_count` number of elements, each of size `elem_size` from
298 `src` to `*target` and uses the `reallocator` to extend the array when necessary.
299 Finally, the size, capacity, and the pointer to the array are all updated and the function returns
300 `CX_ARRAY_SUCCESS`.
302 The third, but extremely rare, return code is `CX_ARRAY_REALLOC_FAILED` and speaks for itself.
304 A few things to note:
305 * `*target` and `src` can point to the same memory region, effectively copying elements within the array with `memmove`
306 * `*target` does not need to point to the start of the array, but `size` and `capacity` always start counting from the
307 position, `*target` points to - in this scenario, specifying a `reallocator` is forbidden for obvious reasons
308 * `index` does not need to be within size of the current array, if `capacity` is specified
309 * `index` does not even need to be within the capacity of the array, if `reallocator` is specified
311 If you just want to add one single element to an existing array, you can use the macro `cx_array_add()`.
312 In that case, since the element is added to the end of the array, the `capacity` argument is mandatory.
313 You can use `CX_ARRAY_DECLARE()` to declare the necessary fields within a structure and then use the
314 `cx_array_simple_*()` convenience macros to reduce code overhead.
316 ## Map
318 *Header file:* [map.h](api/map_8h.html)
320 Similar to the list interface, the map interface provides a common API for implementing maps.
321 There are some minor subtle differences, though.
323 First, the `remove` method is not always a destructive removal.
324 Instead, the last argument is a Boolean that indicates whether the element shall be destroyed or returned.
325 ```c
326 void *(*remove)(CxMap *map, CxHashKey key, bool destroy);
327 ```
328 When you implement this method, you are either supposed to invoke the destructors and return `NULL`,
329 or just remove the element from the map and return it.
331 Secondly, the iterator method is a bit more complete. The signature is as follows:
332 ```c
333 CxIterator (*iterator)(CxMap const *map, enum cx_map_iterator_type type);
334 ```
335 There are three map iterator types: for values, for keys, for pairs.
336 Depending on the iterator type requested, you need to create an iterator with the correct methods that
337 return the requested thing.
338 There are no automatic checks to enforce this - it's completely up to you.
339 If you need inspiration on how to do that, check the hash map implementation that comes with UCX.
341 ### Hash Map
343 *Header file:* [hash_map.h](api/hash__map_8h.html)
345 UCX provides a basic hash map implementation with a configurable amount of buckets.
346 If you do not specify the number of buckets, a default of 16 buckets will be used.
347 You can always rehash the map with `cxMapRehash()` to change the number of buckets to something more efficient,
348 but you need to be careful, because when you use this function you are effectively locking into using this
349 specific hash map implementation, and you would need to remove all calls to this function when you want to
350 exchange the concrete map implementation with something different.
352 ## Utilities
354 *Header file:* [utils.h](api/utils_8h.html)
356 UCX provides some utilities for routine tasks. Most of them are simple macros, like e.g. the `cx_for_n()` macro,
357 creating a `for` loop counting from zero to (n-1) which is extremely useful to traverse the indices of
358 an array.
360 But the most useful utilities are the *stream copy* functions, which provide a simple way to copy all - or a
361 bounded amount of - data from one stream to another. Since the read/write functions of a UCX buffer are
362 fully compatible with stream read/write functions, you can easily transfer data from file or network streams to
363 a UCX buffer or vice-versa.
365 The following example shows, how easy it is to read the contents of a file into a buffer:
366 ```c
367 FILE *inputfile = fopen(infilename, "r");
368 if (inputfile) {
369 CxBuffer fbuf;
370 cxBufferInit(&fbuf, NULL, 4096, NULL, CX_BUFFER_AUTO_EXTEND);
371 cx_stream_copy(inputfile, &fbuf,
372 (cx_read_func) fread,
373 (cx_write_func) cxBufferWrite);
374 fclose(inputfile);
376 // ... do something meaningful with the contents ...
378 cxBufferDestroy(&fbuf);
379 } else {
380 perror("Error opening input file");
381 if (fout != stdout) {
382 fclose(fout);
383 }
384 }
385 ```
387 ### Printf Functions
389 *Header file:* [printf.h](api/printf_8h.html)
391 In this utility header you can find `printf()`-like functions that can write the formatted output to an arbitrary
392 stream (or UCX buffer, resp.), or to memory allocated by an allocator within a single function call.
393 With the help of these convenience functions, you do not need to `snprintf` your string to a temporary buffer anymore,
394 plus you do not need to worry about too small buffer sizes, because the functions will automatically allocate enough
395 memory to contain the entire formatted string.
397 ### Compare Functions
399 *Header file:* [compare.h](api/compare_8h.html)
401 This header file contains a collection of compare functions for various data types.
402 Their signatures are designed to be compatible with the `cx_compare_func` function pointer type.