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Import of Troy Hanson's uthash package, v1.9.6
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utarray: dynamic array macros for C
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===================================
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Troy D. Hanson <thanson@users.sourceforge.net>
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v1.9.5, November 2011
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include::sflogo.txt[]
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include::topnav_utarray.txt[]
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Introduction
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------------
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include::toc.txt[]
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A set of general-purpose dynamic array macros for C structures are included with
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uthash in `utarray.h`. To use these macros in your own C program, just
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copy `utarray.h` into your source directory and use it in your programs.
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#include "utarray.h"
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The dynamic array supports basic operations such as push, pop, and erase on the
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array elements. These array elements can be any simple datatype or structure.
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The array <<operations,operations>> are based loosely on the C++ STL vector methods.
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Internally the dynamic array contains a contiguous memory region into which
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the elements are copied. This buffer is grown as needed using `realloc` to
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accomodate all the data that is pushed into it.
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Download
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~~~~~~~~
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To download the `utarray.h` header file, follow the link on the
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http://uthash.sourceforge.net[uthash home page].
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BSD licensed
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~~~~~~~~~~~~
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This software is made available under the
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link:license.html[revised BSD license].
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It is free and open source.
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Platforms
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~~~~~~~~~
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The 'utarray' macros have been tested on:
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* Linux,
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* Mac OS X,
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* Windows, using Visual Studio 2008 and Visual Studio 2010
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Usage
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-----
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Declaration
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~~~~~~~~~~~
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The array itself has the data type `UT_array`, regardless of the type of
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elements to be stored in it. It is declared like,
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UT_array *nums;
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New and free
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~~~~~~~~~~~~
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The next step is to create the array using `utarray_new`. Later when you're
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done with the array, `utarray_free` will free it and all its elements.
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Push, pop, etc
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~~~~~~~~~~~~~~
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The central features of the utarray involve putting elements into it, taking
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them out, and iterating over them. There are several <<operations,operations>>
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to pick from that deal with either single elements or ranges of elements at a
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time. In the examples below we will use only the push operation to insert
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elements.
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Elements
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--------
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Support for dynamic arrays of integers or strings is especially easy. These are
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best shown by example:
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Integers
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~~~~~~~~
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This example makes a utarray of integers, pushes 0-9 into it, then prints it.
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Lastly it frees it.
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.Integer elements
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-------------------------------------------------------------------------------
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#include <stdio.h>
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#include "utarray.h"
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int main() {
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UT_array *nums;
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int i, *p;
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utarray_new(nums,&ut_int_icd);
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for(i=0; i < 10; i++) utarray_push_back(nums,&i);
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for(p=(int*)utarray_front(nums);
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p!=NULL;
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p=(int*)utarray_next(nums,p)) {
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printf("%d\n",*p);
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}
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utarray_free(nums);
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return 0;
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}
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-------------------------------------------------------------------------------
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The second argument to `utarray_push_back` is always a 'pointer' to the type
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(so a literal cannot be used). So for integers, it is an `int*`.
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Strings
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~~~~~~~
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In this example we make a utarray of strings, push two strings into it, print
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it and free it.
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.String elements
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-------------------------------------------------------------------------------
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#include <stdio.h>
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#include "utarray.h"
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int main() {
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UT_array *strs;
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char *s, **p;
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utarray_new(strs,&ut_str_icd);
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s = "hello"; utarray_push_back(strs, &s);
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s = "world"; utarray_push_back(strs, &s);
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p = NULL;
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while ( (p=(char**)utarray_next(strs,p))) {
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printf("%s\n",*p);
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}
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utarray_free(strs);
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return 0;
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}
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-------------------------------------------------------------------------------
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In this example, since the element is a `char*`, we pass a pointer to it
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(`char**`) as the second argument to `utarray_push_back`. Note that "push" makes
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a copy of the source string and pushes that copy into the array.
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About UT_icd
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~~~~~~~~~~~~
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Arrays be made of any type of element, not just integers and strings. The
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elements can be basic types or structures. Unless you're dealing with integers
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and strings (which use pre-defined `ut_int_icd` and `ut_str_icd`), you'll need
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to define a `UT_icd` helper structure. This structure contains everything that
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utarray needs to initialize, copy or destruct elements.
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typedef struct {
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size_t sz;
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init_f *init;
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ctor_f *copy;
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dtor_f *dtor;
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} UT_icd;
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The three function pointers `init`, `copy`, and `dtor` have these prototypes:
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typedef void (ctor_f)(void *dst, const void *src);
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typedef void (dtor_f)(void *elt);
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typedef void (init_f)(void *elt);
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The `sz` is just the size of the element being stored in the array.
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The `init` function will be invoked whenever utarray needs to initialize an
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empty element. This only happens as a byproduct of `utarray_resize` or
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`utarray_extend_back`. If `init` is `NULL`, it defaults to zero filling the
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new element using memset.
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The `copy` function is used whenever an element is copied into the array.
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It is invoked during `utarray_push_back`, `utarray_insert`, `utarray_inserta`,
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or `utarray_concat`. If `copy` is `NULL`, it defaults to a bitwise copy using
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memcpy.
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The `dtor` function is used to clean up an element that is being removed from
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the array. It may be invoked due to `utarray_resize`, `utarray_pop_back`,
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`utarray_erase`, `utarray_clear`, `utarray_done` or `utarray_free`. If the
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elements need no cleanup upon destruction, `dtor` may be `NULL`.
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Scalar types
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~~~~~~~~~~~~
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The next example uses `UT_icd` with all its defaults to make a utarray of
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`long` elements. This example pushes two longs, prints them, and frees the
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array.
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.long elements
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-------------------------------------------------------------------------------
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#include <stdio.h>
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#include "utarray.h"
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UT_icd long_icd = {sizeof(long), NULL, NULL, NULL };
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int main() {
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UT_array *nums;
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long l, *p;
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utarray_new(nums, &long_icd);
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l=1; utarray_push_back(nums, &l);
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l=2; utarray_push_back(nums, &l);
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p=NULL;
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while( (p=(long*)utarray_next(nums,p))) printf("%ld\n", *p);
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utarray_free(nums);
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return 0;
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}
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-------------------------------------------------------------------------------
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Structures
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~~~~~~~~~~
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Structures can be used as utarray elements. If the structure requires no
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special effort to initialize, copy or destruct, we can use `UT_icd` with all
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its defaults. This example shows a structure that consists of two integers. Here
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we push two values, print them and free the array.
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.Structure (simple)
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-------------------------------------------------------------------------------
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#include <stdio.h>
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#include "utarray.h"
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typedef struct {
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int a;
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int b;
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} intpair_t;
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UT_icd intpair_icd = {sizeof(intpair_t), NULL, NULL, NULL};
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int main() {
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UT_array *pairs;
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intpair_t ip, *p;
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utarray_new(pairs,&intpair_icd);
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ip.a=1; ip.b=2; utarray_push_back(pairs, &ip);
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ip.a=10; ip.b=20; utarray_push_back(pairs, &ip);
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for(p=(intpair_t*)utarray_front(pairs);
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p!=NULL;
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p=(intpair_t*)utarray_next(pairs,p)) {
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printf("%d %d\n", p->a, p->b);
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}
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utarray_free(pairs);
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return 0;
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}
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-------------------------------------------------------------------------------
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The real utility of `UT_icd` is apparent when the elements of the utarray are
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structures that require special work to initialize, copy or destruct.
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For example, when a structure contains pointers to related memory areas that
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need to be copied when the structure is copied (and freed when the structure is
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freed), we can use custom `init`, `copy`, and `dtor` members in the `UT_icd`.
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Here we take an example of a structure that contains an integer and a string.
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When this element is copied (such as when an element is pushed into the array),
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we want to "deep copy" the `s` pointer (so the original element and the new
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element point to their own copies of `s`). When an element is destructed, we
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want to "deep free" its copy of `s`. Lastly, this example is written to work
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even if `s` has the value `NULL`.
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.Structure (complex)
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-------------------------------------------------------------------------------
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#include <stdio.h>
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#include <stdlib.h>
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#include "utarray.h"
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typedef struct {
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int a;
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char *s;
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} intchar_t;
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void intchar_copy(void *_dst, const void *_src) {
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intchar_t *dst = (intchar_t*)_dst, *src = (intchar_t*)_src;
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dst->a = src->a;
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dst->s = src->s ? strdup(src->s) : NULL;
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}
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void intchar_dtor(void *_elt) {
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intchar_t *elt = (intchar_t*)_elt;
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if (elt->s) free(elt->s);
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}
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UT_icd intchar_icd = {sizeof(intchar_t), NULL, intchar_copy, intchar_dtor};
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int main() {
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UT_array *intchars;
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intchar_t ic, *p;
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utarray_new(intchars, &intchar_icd);
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ic.a=1; ic.s="hello"; utarray_push_back(intchars, &ic);
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ic.a=2; ic.s="world"; utarray_push_back(intchars, &ic);
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p=NULL;
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while( (p=(intchar_t*)utarray_next(intchars,p))) {
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printf("%d %s\n", p->a, (p->s ? p->s : "null"));
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}
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utarray_free(intchars);
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return 0;
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}
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-------------------------------------------------------------------------------
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[[operations]]
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Reference
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---------
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This table lists all the utarray operations. These are loosely based on the C++
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vector class.
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Operations
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~~~~~~~~~~
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[width="100%",cols="50<m,40<",grid="none",options="none"]
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|===============================================================================
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| utarray_new(UT_array *a, UT_icd *icd)| allocate a new array
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| utarray_free(UT_array *a) | free an allocated array
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| utarray_init(UT_array *a,UT_icd *icd)| init an array (non-alloc)
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| utarray_done(UT_array *a) | dispose of an array (non-allocd)
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| utarray_reserve(UT_array *a,int n) | ensure space available for 'n' more elements
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| utarray_push_back(UT_array *a,void *p) | push element p onto a
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| utarray_pop_back(UT_array *a) | pop last element from a
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| utarray_extend_back(UT_array *a) | push empty element onto a
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| utarray_len(UT_array *a) | get length of a
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| utarray_eltptr(UT_array *a,int j) | get pointer of element from index
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| utarray_eltidx(UT_array *a,void *e) | get index of element from pointer
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| utarray_insert(UT_array *a,void *p, int j) | insert element p to index j
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| utarray_inserta(UT_array *a,UT_array *w, int j) | insert array w into array a at index j
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| utarray_resize(UT_array *dst,int num) | extend or shrink array to num elements
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| utarray_concat(UT_array *dst,UT_array *src) | copy src to end of dst array
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| utarray_erase(UT_array *a,int pos,int len) | remove len elements from a[pos]..a[pos+len-1]
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| utarray_clear(UT_array *a) | clear all elements from a, setting its length to zero
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| utarray_sort(UT_array *a,cmpfcn *cmp) | sort elements of a using comparison function
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| utarray_find(UT_array *a,void *v, cmpfcn *cmp) | find element v in utarray (must be sorted)
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| utarray_front(UT_array *a) | get first element of a
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| utarray_next(UT_array *a,void *e) | get element of a following e (front if e is NULL)
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| utarray_prev(UT_array *a,void *e) | get element of a before e (back if e is NULL)
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| utarray_back(UT_array *a) | get last element of a
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|===============================================================================
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Notes
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~~~~~
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1. `utarray_new` and `utarray_free` are used to allocate a new array and free it,
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while `utarray_init` and `utarray_done` can be used if the UT_array is already
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allocated and just needs to be initialized or have its internal resources
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freed.
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2. `utarray_reserve` takes the "delta" of elements to reserve (not the total
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desired capacity of the array-- this differs from the C++ STL "reserve" notion)
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3. `utarray_sort` expects a comparison function having the usual `strcmp` -like
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convention where it accepts two elements (a and b) and returns a negative
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value if a precedes b, 0 if a and b sort equally, and positive if b precedes a.
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This is an example of a comparison function:
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int intsort(const void *a,const void*b) {
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int _a = *(int*)a;
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int _b = *(int*)b;
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return _a - _b;
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}
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4. `utarray_find` uses a binary search to locate an element having a certain value
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according to the given comparison function. The utarray must be first sorted
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using the same comparison function. An example of using `utarray_find` with
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a utarray of strings is included in `tests/test61.c`.
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5. A 'pointer' to a particular element (obtained using `utarray_eltptr` or
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`utarray_front`, `utarray_next`, `utarray_prev`, `utarray_back`) becomes invalid whenever
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another element is inserted into the utarray. This is because the internal
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memory management may need to `realloc` the element storage to a new address.
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For this reason, it's usually better to refer to an element by its integer
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'index' in code whose duration may include element insertion.
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// vim: set nowrap syntax=asciidoc:
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