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+---
+title: UCX Features
+---
+
+<div id="modules">
+
+------------------------ ------------------------- ------------------- ---------------------------------
+[Allocator](#allocator) [String](#string) [Buffer](#buffer) [Memory Pool](#memory-pool)
+[Iterator](#iterator) [Collection](#collection) [List](#list) [Map](#map)
+[Utilities](#utilities)
+------------------------ ------------------------- ------------------- ---------------------------------
+
+</div>
+
+## Allocator
+
+*Header file:* [allocator.h](api/allocator_8h.html)
+
+The UCX allocator provides an interface for implementing an own memory allocation mechanism.
+Various function in UCX provide an additional alternative signature that takes an allocator as
+argument. A default allocator implementation using the stdlib memory management functions is
+available via the global symbol `cxDefaultAllocator`.
+
+If you want to define your own allocator, you need to initialize the `CxAllocator` structure
+with a pointer to an allocator class (containing function pointers for the memory management
+functions) and an optional pointer to an arbitrary memory region that can be used to store
+state information for the allocator. An example is shown below:
+
+```c
+struct my_allocator_state {
+ size_t total;
+ size_t avail;
+ char mem[];
+};
+
+static cx_allocator_class my_allocator_class = {
+ my_malloc_impl,
+ my_realloc_impl, // all these functions are somewhere defined
+ my_calloc_impl,
+ my_free_impl
+};
+
+CxAllocator create_my_allocator(size_t n) {
+ CxAllocator alloc;
+ alloc.cl = &my_allocator_class;
+ alloc.data = calloc(1, sizeof(struct my_allocator_state) + n);
+ return alloc;
+}
+```
+
+## String
+
+*Header file:* [string.h](api/string_8h.html)
+
+UCX strings come in two variants: immutable (`cxstring`) and mutable (`cxmutstr`).
+The functions of UCX are designed to work with immutable strings by default but in situations where it is necessary,
+the API also provides alternative functions that work directly with mutable strings.
+Functions that change a string in-place are, of course, only accepting mutable strings.
+
+When you are using UCX functions, or defining your own functions, you are sometimes facing the "problem",
+that the function only accepts arguments of type `cxstring` but you only have a `cxmutstr` at hand.
+In this case you _should not_ introduce a wrapper function that accepts the `cxmutstr`,
+but instead you should use the `cx_strcast()` function to cast the argument to the correct type.
+
+In general, UCX strings are **not** necessarily zero-terminated. If a function guarantees to return zero-terminated
+string, it is explicitly mentioned in the documentation of the respective function.
+As a rule of thumb, you _should not_ pass the strings of a UCX string structure to another API without explicitly
+ensuring that the string is zero-terminated.
+
+## Buffer
+
+*Header file:* [buffer.h](api/buffer_8h.html)
+
+Instances of this buffer implementation can be used to read from or write to memory like you would do with a stream.
+This allows the use of `cx_stream_copy()` (see [Utilities](#utilities)) to copy contents from one buffer to another,
+or from a file or network streams to the buffer and vice-versa.
+
+More features for convenient use of the buffer can be enabled, like automatic memory management and automatic
+resizing of the buffer space.
+
+Since UCX 3.0, the buffer also supports automatic flushing of contents to another stream (or buffer) as an alternative
+to automatically resizing the buffer space.
+Please refer to the API doc for the fields prefixed with `flush_` to learn more.
+
+## Memory Pool
+
+*Header file:* [mempool.h](api/mempool_8h.html)
+
+A memory pool is providing an allocator implementation that automatically deallocates the memory upon its destruction.
+It also allows you to register destructor functions for the allocated memory, which are automatically called before
+the memory is deallocated.
+Additionally, you may also register _independent_ destructor functions within a pool in case some external library
+allocated memory for you, which should be freed together with this pool.
+
+Many UCX features support the use of an allocator.
+The [strings](#string), for instance, provide several functions suffixed with `_a` that allow specifying an allocator.
+You can use this to keep track of the memory occupied by dynamically allocated strings and cleanup everything with
+just a single call to `cxMempoolFree()`.
+
+The following code illustrates this on the example of reading a CSV file into memory.
+```C
+#include <stdio.h>
+#include <cx/mempool.h>
+#include <cx/linked_list.h>
+#include <cx/string.h>
+#include <cx/buffer.h>
+#include <cx/utils.h>
+
+typedef struct {
+ cxstring column_a;
+ cxstring column_b;
+ cxstring column_c;
+} CSVData;
+
+int main(void) {
+ CxMempool* pool = cxBasicMempoolCreate(128);
+
+ FILE *f = fopen("test.csv", "r");
+ if (!f) {
+ perror("Cannot open file");
+ return 1;
+ }
+ // close the file automatically at pool destruction
+ cxMempoolRegister(pool, f, (cx_destructor_func) fclose);
+
+ // create a buffer using the memory pool for destruction
+ CxBuffer *content = cxBufferCreate(NULL, 256, pool->allocator, CX_BUFFER_AUTO_EXTEND);
+
+ // read the file into the buffer and turn it into a string
+ cx_stream_copy(f, content, (cx_read_func) fread, cxBufferWriteFunc);
+ fclose(f);
+ cxstring contentstr = cx_strn(content->space, content->size);
+
+ // split the string into lines - use the mempool for allocating the target array
+ cxstring* lines;
+ size_t lc = cx_strsplit_a(pool->allocator, contentstr,
+ CX_STR("\n"), SIZE_MAX, &lines);
+
+ // skip the header and parse the remaining data into a linked list
+ // the nodes of the linked list shall also be allocated by the mempool
+ CxList* datalist = cxLinkedListCreate(pool->allocator, NULL, sizeof(CSVData));
+ for (size_t i = 1 ; i < lc ; i++) {
+ if (lines[i].length == 0) continue;
+ cxstring fields[3];
+ size_t fc = cx_strsplit(lines[i], CX_STR(";"), 3, fields);
+ if (fc != 3) {
+ fprintf(stderr, "Syntax error in line %zu.\n", i);
+ cxMempoolFree(pool);
+ return 1;
+ }
+ CSVData data;
+ data.column_a = fields[0];
+ data.column_b = fields[1];
+ data.column_c = fields[2];
+ cxListAdd(datalist, &data);
+ }
+
+ // iterate through the list and output the data
+ CxIterator iter = cxListIterator(datalist);
+ cx_foreach(CSVData*, data, iter) {
+ printf("Column A: %.*s | "
+ "Column B: %.*s | "
+ "Column C: %.*s\n",
+ (int)data->column_a.length, data->column_a.ptr,
+ (int)data->column_b.length, data->column_b.ptr,
+ (int)data->column_c.length, data->column_c.ptr
+ );
+ }
+
+ // cleanup everything, no manual free() needed
+ cxMempoolFree(pool);
+
+ return 0;
+}
+```
+
+## Iterator
+
+*Header file:* [iterator.h](api/iterator_8h.html)
+
+In UCX 3 a new feature has been introduced to write own iterators, that work with the `cx_foreach` macro.
+In previous UCX releases there were different hard-coded foreach macros for lists and maps that were not customizable.
+Now, creating an iterator is as simple as creating a `CxIterator` struct and setting the fields in a meaningful way.
+
+You do not always need all fields in the iterator structure, depending on your use case.
+Sometimes you only need the `index` (for example when iterating over simple lists), and other times you will need the
+`slot` and `kv_data` fields (for example when iterating over maps).
+
+If the predefined fields are insufficient for your use case, you can alternatively create your own iterator structure
+and place the `CX_ITERATOR_BASE` macro as first member of that structure.
+
+Usually an iterator is not mutating the collection it is iterating over.
+In some programming languages it is even disallowed to change the collection while iterating with foreach.
+But sometimes it is desirable to remove an element from the collection while iterating over it.
+For this purpose, most collections allow the creation of a _mutating_ iterator.
+The only differences are, that the `mutating` flag is `true` and the `src_handle` is not const.
+On mutating iterators it is allowed to call the `cxFlagForRemoval()` function, which instructs the iterator to remove
+the current element from the collection on the next call to `cxIteratorNext()` and clear the flag afterward.
+If you are implementing your own iterator, it is up to you to implement this behavior.
+
+## Collection
+
+*Header file:* [collection.h](api/collection_8h.html)
+
+Collections in UCX 3 have several common features.
+If you want to implement an own collection data type that uses the same features, you can use the
+`CX_COLLECTION_BASE` macro at the beginning of your struct to roll out all members a usual UCX collection has.
+```c
+struct my_fancy_collection_s {
+ CX_COLLECTION_BASE;
+ struct my_collection_data_s *data;
+};
+```
+Based on this structure, this header provides some convenience macros for invoking the destructor functions
+that are part of the basic collection members.
+The idea of having destructor functions within a collection is that you can destroy the collection _and_ the
+contents with one single function call.
+When you are implementing a collection, you are responsible for invoking the destructors at the right places, e.g.
+when removing (and deleting) elements in the collection, clearing the collection, or - the most prominent case -
+destroying the collection.
+
+You can always look at the UCX list and map implementations if you need some inspiration.
+
+## List
+
+*Header file:* [list.h](api/list_8h.html)
+
+This header defines a common interface for all list implementations.
+
+UCX already comes with two common list implementations (linked list and array list) that should cover most use cases.
+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
+`struct cx_list_s` as first member, and set an appropriate list class that implements the functionality.
+It is strongly recommended that this class is shared among all instances of the same list type, because otherwise
+the `cxListCompare` function cannot use the optimized implementation of your class and will instead fall back to
+using iterators to compare the contents element-wise.
+
+### Linked List
+
+*Header file:* [linked_list.h](api/linked__list_8h.html)
+
+On top of implementing the list interface, this header also defines several low-level functions that
+work with arbitrary structures.
+Low-level functions, in contrast to the high-level list interface, can easily be recognized by their snake-casing.
+The function `cx_linked_list_at`, for example, implements a similar functionality like `cxListAt`, but operates
+on arbitrary structures.
+The following snippet shows how it is used.
+All other low-level functions work similarly.
+```c
+struct node {
+ node *next;
+ node *prev;
+ int data;
+};
+
+const ptrdiff_t loc_prev = offsetof(struct node, prev);
+const ptrdiff_t loc_next = offsetof(struct node, next);
+const ptrdiff_t loc_data = offsetof(struct node, data);
+
+struct node a = {0}, b = {0}, c = {0}, d = {0};
+cx_linked_list_link(&a, &b, loc_prev, loc_next);
+cx_linked_list_link(&b, &c, loc_prev, loc_next);
+cx_linked_list_link(&c, &d, loc_prev, loc_next);
+
+cx_linked_list_at(&a, 0, loc_next, 2); // returns pointer to c
+```
+
+### Array List
+
+*Header file:* [array_list.h](api/array__list_8h.html)
+
+Since low-level array lists are just plain arrays, there is no need for such many low-level functions as for linked
+lists.
+However, there is one extremely powerful function that can be used for several complex tasks: `cx_array_copy`.
+The full signature is shown below:
+```c
+int cx_array_copy(
+ void **target,
+ void *size,
+ void *capacity,
+ unsigned width,
+ size_t index,
+ const void *src,
+ size_t elem_size,
+ size_t elem_count,
+ struct cx_array_reallocator_s *reallocator
+);
+```
+The `target` argument is a pointer to the target array pointer.
+The reason for this additional indirection is that this function writes
+back the pointer to the possibly reallocated array.
+The next two arguments are pointers to the `size` and `capacity` of the target array for which the width
+(in bits) is specified in the `width` argument.
+
+On a successful invocation, the function copies `elem_count` number of elements, each of size `elem_size` from
+`src` to `*target` and uses the `reallocator` to extend the array when necessary.
+Finally, the size, capacity, and the pointer to the array are all updated and the function returns zero.
+
+A few things to note:
+* `*target` and `src` can point to the same memory region, effectively copying elements within the array with `memmove`
+* `*target` does not need to point to the start of the array, but `size` and `capacity` always start counting from the
+ position, `*target` points to - in this scenario, the need for reallocation must be avoided for obvious reasons
+* `index` does not need to be within size of the current array
+* `index` does not even need to be within the capacity of the array
+* `width` must be one of 8, 16, 32, 64 (only on 64-bit systems), or zero (in which case the native word width is used)
+
+If you just want to add one single element to an existing array, you can use the macro `cx_array_add()`.
+You can use `CX_ARRAY_DECLARE()` to declare the necessary fields within a structure and then use the
+`cx_array_simple_*()` convenience macros to reduce code overhead.
+The convenience macros automatically determine the width of the size/capacity variables.
+
+## Map
+
+*Header file:* [map.h](api/map_8h.html)
+
+Similar to the list interface, the map interface provides a common API for implementing maps.
+There are some minor subtle differences, though.
+
+First, the `remove` method is not always a destructive removal.
+Instead, the last argument is a Boolean that indicates whether the element shall be destroyed or returned.
+```c
+void *(*remove)(CxMap *map, CxHashKey key, bool destroy);
+```
+When you implement this method, you are either supposed to invoke the destructors and return `NULL`,
+or just remove the element from the map and return it.
+
+Secondly, the iterator method is a bit more complete. The signature is as follows:
+```c
+CxIterator (*iterator)(const CxMap *map, enum cx_map_iterator_type type);
+```
+There are three map iterator types: for values, for keys, for pairs.
+Depending on the iterator type requested, you need to create an iterator with the correct methods that
+return the requested thing.
+There are no automatic checks to enforce this - it's completely up to you.
+If you need inspiration on how to do that, check the hash map implementation that comes with UCX.
+
+### Hash Map
+
+*Header file:* [hash_map.h](api/hash__map_8h.html)
+
+UCX provides a basic hash map implementation with a configurable amount of buckets.
+If you do not specify the number of buckets, a default of 16 buckets will be used.
+You can always rehash the map with `cxMapRehash()` to change the number of buckets to something more efficient,
+but you need to be careful, because when you use this function you are effectively locking into using this
+specific hash map implementation, and you would need to remove all calls to this function when you want to
+exchange the concrete map implementation with something different.
+
+## Utilities
+
+*Header file:* [utils.h](api/utils_8h.html)
+
+UCX provides some utilities for routine tasks.
+
+The most useful utilities are the *stream copy* functions, which provide a simple way to copy all - or a
+bounded amount of - data from one stream to another. Since the read/write functions of a UCX buffer are
+fully compatible with stream read/write functions, you can easily transfer data from file or network streams to
+a UCX buffer or vice-versa.
+
+The following example shows, how easy it is to read the contents of a file into a buffer:
+```c
+FILE *inputfile = fopen(infilename, "r");
+if (inputfile) {
+ CxBuffer fbuf;
+ cxBufferInit(&fbuf, NULL, 4096, NULL, CX_BUFFER_AUTO_EXTEND);
+ cx_stream_copy(inputfile, &fbuf,
+ (cx_read_func) fread,
+ cxBufferWriteFunc);
+ fclose(inputfile);
+
+ // ... do something meaningful with the contents ...
+
+ cxBufferDestroy(&fbuf);
+} else {
+ perror("Error opening input file");
+ if (fout != stdout) {
+ fclose(fout);
+ }
+}
+```
+
+### Printf Functions
+
+*Header file:* [printf.h](api/printf_8h.html)
+
+In this utility header you can find `printf()`-like functions that can write the formatted output to an arbitrary
+stream (or UCX buffer, resp.), or to memory allocated by an allocator within a single function call.
+With the help of these convenience functions, you do not need to `snprintf` your string to a temporary buffer anymore,
+plus you do not need to worry about too small buffer sizes, because the functions will automatically allocate enough
+memory to contain the entire formatted string.
+
+### Compare Functions
+
+*Header file:* [compare.h](api/compare_8h.html)
+
+This header file contains a collection of compare functions for various data types.
+Their signatures are designed to be compatible with the `cx_compare_func` function pointer type.