Sun, 03 Sep 2023 09:10:16 +0200
make C++ compiler and pandoc entirely optional
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 Usually an iterator is not mutating the collection it is iterating over.
190 In some programming languages it is even disallowed to change the collection while iterating with foreach.
191 But sometimes it is desirable to remove an element from the collection while iterating over it.
192 This is, what the `CxMutIterator` is for.
193 The only differences are, that the `mutating` flag is `true` and the `src_handle` is not const.
194 On mutating iterators it is allowed to call the `cxFlagForRemoval()` function, which instructs the iterator to remove
195 the current element from the collection on the next call to `cxIteratorNext()` and clear the flag afterward.
196 If you are implementing your own iterator, it is up to you to implement this behavior in your `next` method, or
197 make the implementation of the `flag_removal` method always return `false`.
199 ## Collection
201 *Header file:* [collection.h](api/collection_8h.html)
203 Collections in UCX 3 have several common features.
204 If you want to implement an own collection data type that uses the same features, you can use the
205 `CX_COLLECTION_MEMBERS` macro at the beginning of your struct to roll out all members a usual UCX collection has.
206 ```c
207 struct my_fancy_collection_s {
208 CX_COLLECTION_MEMBERS
209 struct my_collection_data_s *data;
210 };
211 ```
212 Based on this structure, this header provides some convenience macros for invoking the destructor functions
213 that are part of the basic collection members.
214 The idea of having destructor functions within a collection is that you can destroy the collection _and_ the
215 contents with one single function call.
216 When you are implementing a collection, you are responsible for invoking the destructors at the right places, e.g.
217 when removing (and deleting) elements in the collection, clearing the collection, or - the most prominent case -
218 destroying the collection.
220 You can always look at the UCX list and map implementations if you need some inspiration.
222 ## List
224 *Header file:* [list.h](api/list_8h.html)
226 This header defines a common interface for all list implementations, which is basically as simple as the following
227 structure.
228 ```c
229 struct cx_list_s {
230 CX_COLLECTION_MEMBERS // size, capacity, etc.
231 cx_list_class const *cl; // The list class definition
232 };
233 ```
234 The actual structure contains one more class pointer that is used when wrapping a list into a pointer-aware list
235 with `cxListStorePointers()`. What this means, is that - if you want to implement your own list structure - you
236 only need to cover the case where the list is storing copies of your objects.
238 UCX comes with two common list implementations (linked list and array list) that should cover most use cases.
239 But if you feel the need to implement an own list, the only thing you need to do is to define a struct where
240 `struct cx_list_s`, and set an appropriate list class that implements the functionality.
241 It is strongly recommended that this class is shared among all instances of the same list type, because otherwise
242 the `cxListCompare` function cannot use the optimized implementation of your class and will instead fall back to
243 using iterators to compare the contents element-wise.
245 ### Linked List
247 *Header file:* [linked_list.h](api/linked__list_8h.html)
249 On top of implementing the list interface, this header also defines several low-level functions that
250 work with arbitrary structures.
251 Low-level functions, in contrast to the high-level list interface, can easily be recognized by their snake-casing.
252 The function `cx_linked_list_at`, for example, implements a similar functionality like `cxListAt`, but operates
253 on arbitrary structures.
254 The following snippet shows how it is used.
255 All other low-level functions work similarly.
256 ```c
257 struct node {
258 node *next;
259 node *prev;
260 int data;
261 };
263 const ptrdiff_t loc_prev = offsetof(struct node, prev);
264 const ptrdiff_t loc_next = offsetof(struct node, next);
265 const ptrdiff_t loc_data = offsetof(struct node, data);
267 struct node a = {0}, b = {0}, c = {0}, d = {0};
268 cx_linked_list_link(&a, &b, loc_prev, loc_next);
269 cx_linked_list_link(&b, &c, loc_prev, loc_next);
270 cx_linked_list_link(&c, &d, loc_prev, loc_next);
272 cx_linked_list_at(&a, 0, loc_next, 2); // returns pointer to c
273 ```
275 ### Array List
277 *Header file:* [array_list.h](api/array__list_8h.html)
279 Since low-level array lists are just plain arrays, there is no need for such many low-level functions as for linked
280 lists.
281 However, there is one extremely powerful function that can be used for several complex tasks: `cx_array_copy`.
282 The full signature is shown below:
283 ```c
284 enum cx_array_copy_result cx_array_copy(
285 void **target,
286 size_t *size,
287 size_t *capacity, // optional
288 size_t index,
289 void const *src,
290 size_t elem_size,
291 size_t elem_count,
292 struct cx_array_reallocator_s *reallocator // optional
293 );
294 ```
295 The `target` argument is a pointer to the target array pointer.
296 The reason for this additional indirection is that - given that you provide a `reallocator` - this function writes
297 back the pointer to the possibly reallocated array.
298 THe next two arguments are pointers to the `size` and `capacity` of the target array.
299 Tracking the capacity is optional.
300 If you do not specify a pointer for the capacity, automatic reallocation of the array is entirely disabled (i.e. it
301 does not make sense to specify a `reallocator` then).
302 In this case, the function cannot copy more than `size-index` elements and if you try, it will return
303 `CX_ARRAY_COPY_REALLOC_NOT_SUPPORTED` and do nothing.
305 On a successful invocation, the function copies `elem_count` number of elements, each of size `elem_size` from
306 `src` to `*target` and uses the `reallocator` to extend the array when necessary.
307 Finally, the size, capacity, and the pointer to the array are all updated and the function returns
308 `CX_ARRAY_COPY_SUCCESS`.
310 The third, but extremely rare, return code is `CX_ARRAY_COPY_REALLOC_FAILED` and speaks for itself.
312 A few things to note:
313 * `*target` and `src` can point to the same memory region, effectively copying elements within the array with `memmove`
314 * `*target` does not need to point to the start of the array, but `size` and `capacity` always start counting from the
315 position, `*target` points to - in this scenario, specifying a `reallocator` is forbidden for obvious reasons
316 * `index` does not need to be within size of the current array, if `capacity` is specified
317 * `index` does not even need to be within the capacity of the array, if `reallocator` is specified
320 ## Map
322 *Header file:* [map.h](api/map_8h.html)
324 Similar to the list interface, the map interface provides a common API for implementing maps.
325 There are some minor subtle differences, though.
327 First, the `remove` method is not always a destructive removal.
328 Instead, the last argument is a Boolean that indicates whether the element shall be destroyed or returned.
329 ```c
330 void *(*remove)(CxMap *map, CxHashKey key, bool destroy);
331 ```
332 When you implement this method, you are either supposed to invoke the destructors and return `NULL`,
333 or just remove the element from the map and return it.
335 Secondly, the iterator method is a bit more complete. The signature is as follows:
336 ```c
337 CxIterator (*iterator)(CxMap const *map, enum cx_map_iterator_type type);
338 ```
339 There are three map iterator types: for values, for keys, for pairs.
340 Depending on the iterator type requested, you need to create an iterator with the correct methods that
341 return the requested thing.
342 There are no automatic checks to enforce this - it's completely up to you.
343 If you need inspiration on how to do that, check the hash map implementation that comes with UCX.
345 ### Hash Map
347 *Header file:* [hash_map.h](api/hash__map_8h.html)
349 UCX provides a basic hash map implementation with a configurable amount of buckets.
350 If you do not specify the number of buckets, a default of 16 buckets will be used.
351 You can always rehash the map with `cxMapRehash()` to change the number of buckets to something more efficient,
352 but you need to be careful, because when you use this function you are effectively locking into using this
353 specific hash map implementation, and you would need to remove all calls to this function when you want to
354 exchange the concrete map implementation with something different.
356 ## Utilities
358 *Header file:* [utils.h](api/utils_8h.html)
360 UCX provides some utilities for routine tasks. Most of them are simple macros, like e.g. the `cx_for_n()` macro,
361 creating a `for` loop counting from zero to (n-1) which is extremely useful to traverse the indices of
362 an array.
364 But the most useful utilities are the *stream copy* functions, which provide a simple way to copy all - or a
365 bounded amount of - data from one stream to another. Since the read/write functions of a UCX buffer are
366 fully compatible with stream read/write functions, you can easily transfer data from file or network streams to
367 a UCX buffer or vice-versa.
369 The following example shows, how easy it is to read the contents of a file into a buffer:
370 ```c
371 FILE *inputfile = fopen(infilename, "r");
372 if (inputfile) {
373 CxBuffer fbuf;
374 cxBufferInit(&fbuf, NULL, 4096, NULL, CX_BUFFER_AUTO_EXTEND);
375 cx_stream_copy(inputfile, &fbuf,
376 (cx_read_func) fread,
377 (cx_write_func) cxBufferWrite);
378 fclose(inputfile);
380 // ... do something meaningful with the contents ...
382 cxBufferDestroy(&fbuf);
383 } else {
384 perror("Error opening input file");
385 if (fout != stdout) {
386 fclose(fout);
387 }
388 }
389 ```
391 ### Printf Functions
393 *Header file:* [printf.h](api/printf_8h.html)
395 In this utility header you can find `printf()`-like functions that can write the formatted output to an arbitrary
396 stream (or UCX buffer, resp.), or to memory allocated by an allocator within a single function call.
397 With the help of these convenience functions, you do not need to `snprintf` your string to a temporary buffer anymore,
398 plus you do not need to worry about too small buffer sizes, because the functions will automatically allocate enough
399 memory to contain the entire formatted string.
401 ### Compare Functions
403 *Header file:* [compare.h](api/compare_8h.html)
405 This header file contains a collection of compare functions for various data types.
406 Their signatures are designed to be compatible with the `cx_compare_func` function pointer type.