|
- utringbuffer: dynamic ring-buffer macros for C
- ==============================================
- Arthur O'Dwyer <arthur.j.odwyer@gmail.com>
- v2.3.0, February 2021
-
- Here's a link back to the https://github.com/troydhanson/uthash[GitHub project page].
-
- Introduction
- ------------
- The functions in `utringbuffer.h` are based on the general-purpose array macros
- provided in `utarray.h`, so before reading this page you should read
- link:utarray.html[that page] first.
-
- To use these macros in your own C program, copy both `utarray.h` and `utringbuffer.h`
- into your source directory and use `utringbuffer.h` in your program.
-
- #include "utringbuffer.h"
-
- The provided <<operations,operations>> are based loosely on the C++ STL vector methods.
- The ring-buffer data type supports construction (with a specified capacity),
- destruction, iteration, and push, but not pop; once the ring-buffer reaches full
- capacity, pushing a new element automatically pops and destroys the oldest element.
- The elements contained in the ring-buffer can be any simple datatype or structure.
-
- Internally the ring-buffer contains a pre-allocated memory region into which the
- elements are copied, starting at position 0. When the ring-buffer reaches full
- capacity, the next element to be pushed is pushed at position 0, overwriting the
- oldest element, and the internal index representing the "start" of the ring-buffer
- is incremented. A ring-buffer, once full, can never become un-full.
-
-
- Download
- ~~~~~~~~
- To download the `utringbuffer.h` header file,
- follow the links on https://github.com/troydhanson/uthash to clone uthash or get a zip file,
- then look in the src/ sub-directory.
-
- BSD licensed
- ~~~~~~~~~~~~
- This software is made available under the
- link:license.html[revised BSD license].
- It is free and open source.
-
- Platforms
- ~~~~~~~~~
- The 'utringbuffer' macros have been tested on:
-
- * Linux,
- * Mac OS X,
- * Windows, using Visual Studio 2008 and Visual Studio 2010
-
- Usage
- -----
-
- Declaration
- ~~~~~~~~~~~
-
- The ring-buffer itself has the data type `UT_ringbuffer`, regardless of the type of
- elements to be stored in it. It is declared like,
-
- UT_ringbuffer *history;
-
- New and free
- ~~~~~~~~~~~~
- The next step is to create the ring-buffer using `utringbuffer_new`. Later when you're
- done with the ring-buffer, `utringbuffer_free` will free it and all its elements.
-
- Push, etc
- ~~~~~~~~~
- The central features of the ring-buffer involve putting elements into it
- and iterating over them. There are several <<operations,operations>>
- that deal with either single elements or ranges of elements at a
- time. In the examples below we will use only the push operation to insert
- elements.
-
- Elements
- --------
-
- Support for dynamic arrays of integers or strings is especially easy. These are
- best shown by example:
-
- Integers
- ~~~~~~~~
- This example makes a ring-buffer of integers, pushes 0-9 into it, then prints it
- two different ways. Lastly it frees it.
-
- .Integer elements
- -------------------------------------------------------------------------------
- #include <stdio.h>
- #include "utringbuffer.h"
-
- int main() {
- UT_ringbuffer *history;
- int i, *p;
-
- utringbuffer_new(history, 7, &ut_int_icd);
- for(i=0; i < 10; i++) utringbuffer_push_back(history, &i);
-
- for (p = (int*)utringbuffer_front(history);
- p != NULL;
- p = (int*)utringbuffer_next(history, p)) {
- printf("%d\n", *p); /* prints "3 4 5 6 7 8 9" */
- }
-
- for (i=0; i < utringbuffer_len(history); i++) {
- p = utringbuffer_eltptr(history, i);
- printf("%d\n", *p); /* prints "3 4 5 6 7 8 9" */
- }
-
- utringbuffer_free(history);
-
- return 0;
- }
- -------------------------------------------------------------------------------
-
- The second argument to `utringbuffer_push_back` is always a 'pointer' to the type
- (so a literal cannot be used). So for integers, it is an `int*`.
-
- Strings
- ~~~~~~~
- In this example we make a ring-buffer of strings, push two strings into it, print
- it and free it.
-
- .String elements
- -------------------------------------------------------------------------------
- #include <stdio.h>
- #include "utringbuffer.h"
-
- int main() {
- UT_ringbuffer *strs;
- char *s, **p;
-
- utringbuffer_new(strs, 7, &ut_str_icd);
-
- s = "hello"; utringbuffer_push_back(strs, &s);
- s = "world"; utringbuffer_push_back(strs, &s);
- p = NULL;
- while ( (p=(char**)utringbuffer_next(strs,p))) {
- printf("%s\n",*p);
- }
-
- utringbuffer_free(strs);
-
- return 0;
- }
- -------------------------------------------------------------------------------
-
- In this example, since the element is a `char*`, we pass a pointer to it
- (`char**`) as the second argument to `utringbuffer_push_back`. Note that "push" makes
- a copy of the source string and pushes that copy into the array.
-
- About UT_icd
- ~~~~~~~~~~~~
-
- Arrays can be made of any type of element, not just integers and strings. The
- elements can be basic types or structures. Unless you're dealing with integers
- and strings (which use pre-defined `ut_int_icd` and `ut_str_icd`), you'll need
- to define a `UT_icd` helper structure. This structure contains everything that
- utringbuffer (or utarray) needs to initialize, copy or destruct elements.
-
- typedef struct {
- size_t sz;
- init_f *init;
- ctor_f *copy;
- dtor_f *dtor;
- } UT_icd;
-
- The three function pointers `init`, `copy`, and `dtor` have these prototypes:
-
- typedef void (ctor_f)(void *dst, const void *src);
- typedef void (dtor_f)(void *elt);
- typedef void (init_f)(void *elt);
-
- The `sz` is just the size of the element being stored in the array.
-
- The `init` function is used by utarray but is never used by utringbuffer;
- you may safely set it to any value you want.
-
- The `copy` function is used whenever an element is copied into the buffer.
- It is invoked during `utringbuffer_push_back`.
- If `copy` is `NULL`, it defaults to a bitwise copy using memcpy.
-
- The `dtor` function is used to clean up an element that is being removed from
- the buffer. It may be invoked due to `utringbuffer_push_back` (on the oldest
- element in the buffer), `utringbuffer_clear`, `utringbuffer_done`, or
- `utringbuffer_free`.
- If the elements need no cleanup upon destruction, `dtor` may be `NULL`.
-
- Scalar types
- ~~~~~~~~~~~~
-
- The next example uses `UT_icd` with all its defaults to make a ring-buffer of
- `long` elements. This example pushes two longs into a buffer of capacity 1,
- prints the contents of the buffer (which is to say, the most recent value
- pushed), and then frees the buffer.
-
- .long elements
- -------------------------------------------------------------------------------
- #include <stdio.h>
- #include "utringbuffer.h"
-
- UT_icd long_icd = {sizeof(long), NULL, NULL, NULL };
-
- int main() {
- UT_ringbuffer *nums;
- long l, *p;
- utringbuffer_new(nums, 1, &long_icd);
-
- l=1; utringbuffer_push_back(nums, &l);
- l=2; utringbuffer_push_back(nums, &l);
-
- p=NULL;
- while((p = (long*)utringbuffer_next(nums,p))) printf("%ld\n", *p);
-
- utringbuffer_free(nums);
- return 0;
- }
- -------------------------------------------------------------------------------
-
- Structures
- ~~~~~~~~~~
-
- Structures can be used as utringbuffer elements. If the structure requires no
- special effort to initialize, copy or destruct, we can use `UT_icd` with all
- its defaults. This example shows a structure that consists of two integers. Here
- we push two values, print them and free the buffer.
-
- .Structure (simple)
- -------------------------------------------------------------------------------
- #include <stdio.h>
- #include "utringbuffer.h"
-
- typedef struct {
- int a;
- int b;
- } intpair_t;
-
- UT_icd intpair_icd = {sizeof(intpair_t), NULL, NULL, NULL};
-
- int main() {
-
- UT_ringbuffer *pairs;
- intpair_t ip, *p;
- utringbuffer_new(pairs, 7, &intpair_icd);
-
- ip.a=1; ip.b=2; utringbuffer_push_back(pairs, &ip);
- ip.a=10; ip.b=20; utringbuffer_push_back(pairs, &ip);
-
- for(p=(intpair_t*)utringbuffer_front(pairs);
- p!=NULL;
- p=(intpair_t*)utringbuffer_next(pairs,p)) {
- printf("%d %d\n", p->a, p->b);
- }
-
- utringbuffer_free(pairs);
- return 0;
- }
- -------------------------------------------------------------------------------
-
- The real utility of `UT_icd` is apparent when the elements stored in the
- ring-buffer are structures that require special work to initialize, copy or
- destruct.
-
- For example, when a structure contains pointers to related memory areas that
- need to be copied when the structure is copied (and freed when the structure is
- freed), we can use custom `init`, `copy`, and `dtor` members in the `UT_icd`.
-
- Here we take an example of a structure that contains an integer and a string.
- When this element is copied (such as when an element is pushed),
- we want to "deep copy" the `s` pointer (so the original element and the new
- element point to their own copies of `s`). When an element is destructed, we
- want to "deep free" its copy of `s`. Lastly, this example is written to work
- even if `s` has the value `NULL`.
-
- .Structure (complex)
- -------------------------------------------------------------------------------
- #include <stdio.h>
- #include <stdlib.h>
- #include "utringbuffer.h"
-
- typedef struct {
- int a;
- char *s;
- } intchar_t;
-
- void intchar_copy(void *_dst, const void *_src) {
- intchar_t *dst = (intchar_t*)_dst, *src = (intchar_t*)_src;
- dst->a = src->a;
- dst->s = src->s ? strdup(src->s) : NULL;
- }
-
- void intchar_dtor(void *_elt) {
- intchar_t *elt = (intchar_t*)_elt;
- free(elt->s);
- }
-
- UT_icd intchar_icd = {sizeof(intchar_t), NULL, intchar_copy, intchar_dtor};
-
- int main() {
- UT_ringbuffer *intchars;
- intchar_t ic, *p;
- utringbuffer_new(intchars, 2, &intchar_icd);
-
- ic.a=1; ic.s="hello"; utringbuffer_push_back(intchars, &ic);
- ic.a=2; ic.s="world"; utringbuffer_push_back(intchars, &ic);
- ic.a=3; ic.s="peace"; utringbuffer_push_back(intchars, &ic);
-
- p=NULL;
- while( (p=(intchar_t*)utringbuffer_next(intchars,p))) {
- printf("%d %s\n", p->a, (p->s ? p->s : "null"));
- /* prints "2 world 3 peace" */
- }
-
- utringbuffer_free(intchars);
- return 0;
- }
-
- -------------------------------------------------------------------------------
-
- [[operations]]
- Reference
- ---------
- This table lists all the utringbuffer operations. These are loosely based on the C++
- vector class.
-
- Operations
- ~~~~~~~~~~
-
- [width="100%",cols="50<m,40<",grid="none",options="none"]
- |===============================================================================
- | utringbuffer_new(UT_ringbuffer *a, int n, UT_icd *icd) | allocate a new ringbuffer
- | utringbuffer_free(UT_ringbuffer *a) | free an allocated ringbuffer
- | utringbuffer_init(UT_ringbuffer *a, int n, UT_icd *icd) | init a ringbuffer (non-alloc)
- | utringbuffer_done(UT_ringbuffer *a) | dispose of a ringbuffer (non-alloc)
- | utringbuffer_clear(UT_ringbuffer *a) | clear all elements from a, making it empty
- | utringbuffer_push_back(UT_ringbuffer *a, element *p) | push element p onto a
- | utringbuffer_len(UT_ringbuffer *a) | get length of a
- | utringbuffer_empty(UT_ringbuffer *a) | get whether a is empty
- | utringbuffer_full(UT_ringbuffer *a) | get whether a is full
- | utringbuffer_eltptr(UT_ringbuffer *a, int j) | get pointer of element from index
- | utringbuffer_eltidx(UT_ringbuffer *a, element *e) | get index of element from pointer
- | utringbuffer_front(UT_ringbuffer *a) | get oldest element of a
- | utringbuffer_next(UT_ringbuffer *a, element *e) | get element of a following e (front if e is NULL)
- | utringbuffer_prev(UT_ringbuffer *a, element *e) | get element of a before e (back if e is NULL)
- | utringbuffer_back(UT_ringbuffer *a) | get newest element of a
- |===============================================================================
-
- Notes
- ~~~~~
-
- 1. `utringbuffer_new` and `utringbuffer_free` are used to allocate a new ring-buffer
- and to free it,
- while `utringbuffer_init` and `utringbuffer_done` can be used if the UT_ringbuffer
- is already allocated and just needs to be initialized or have its internal resources
- freed.
- 2. Both `utringbuffer_new` and `utringbuffer_init` take a second parameter `n` indicating
- the capacity of the ring-buffer, that is, the size at which the ring-buffer is considered
- "full" and begins to overwrite old elements with newly pushed ones.
- 3. Once a ring-buffer has become full, it will never again become un-full except by
- means of `utringbuffer_clear`. There is no way to "pop" a single old item from the
- front of the ring-buffer. You can simulate this ability by maintaining a separate
- integer count of the number of "logically popped elements", and starting your iteration
- with `utringbuffer_eltptr(a, popped_count)` instead of with `utringbuffer_front(a)`.
- 4. Pointers to elements (obtained using `utringbuffer_eltptr`, `utringbuffer_front`,
- `utringbuffer_next`, etc.) are not generally invalidated by `utringbuffer_push_back`,
- because utringbuffer does not perform reallocation; however, a pointer to the oldest
- element may suddenly turn into a pointer to the 'newest' element if
- `utringbuffer_push_back` is called while the buffer is full.
- 5. The elements of a ring-buffer are stored in contiguous memory, but once the ring-buffer
- has become full, it is no longer true that the elements are contiguously in order from
- oldest to newest; i.e., `(element *)utringbuffer_front(a) + utringbuffer_len(a)-1` is
- not generally equal to `(element *)utringbuffer_back(a)`.
-
- // vim: set nowrap syntax=asciidoc:
|