109 lines
4.9 KiB
HTML
109 lines
4.9 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- This manual is for FFTW
|
|
(version 3.3.10, 10 December 2020).
|
|
|
|
Copyright (C) 2003 Matteo Frigo.
|
|
|
|
Copyright (C) 2003 Massachusetts Institute of Technology.
|
|
|
|
Permission is granted to make and distribute verbatim copies of this
|
|
manual provided the copyright notice and this permission notice are
|
|
preserved on all copies.
|
|
|
|
Permission is granted to copy and distribute modified versions of this
|
|
manual under the conditions for verbatim copying, provided that the
|
|
entire resulting derived work is distributed under the terms of a
|
|
permission notice identical to this one.
|
|
|
|
Permission is granted to copy and distribute translations of this manual
|
|
into another language, under the above conditions for modified versions,
|
|
except that this permission notice may be stated in a translation
|
|
approved by the Free Software Foundation. -->
|
|
<!-- Created by GNU Texinfo 6.7, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<title>Dynamic Arrays in C (FFTW 3.3.10)</title>
|
|
|
|
<meta name="description" content="Dynamic Arrays in C (FFTW 3.3.10)">
|
|
<meta name="keywords" content="Dynamic Arrays in C (FFTW 3.3.10)">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<link href="index.html" rel="start" title="Top">
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="Multi_002ddimensional-Array-Format.html" rel="up" title="Multi-dimensional Array Format">
|
|
<link href="Dynamic-Arrays-in-C_002dThe-Wrong-Way.html" rel="next" title="Dynamic Arrays in C-The Wrong Way">
|
|
<link href="Fixed_002dsize-Arrays-in-C.html" rel="prev" title="Fixed-size Arrays in C">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.indentedblock {margin-right: 0em}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
kbd {font-style: oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
span.nolinebreak {white-space: nowrap}
|
|
span.roman {font-family: initial; font-weight: normal}
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<span id="Dynamic-Arrays-in-C"></span><div class="header">
|
|
<p>
|
|
Next: <a href="Dynamic-Arrays-in-C_002dThe-Wrong-Way.html" accesskey="n" rel="next">Dynamic Arrays in C-The Wrong Way</a>, Previous: <a href="Fixed_002dsize-Arrays-in-C.html" accesskey="p" rel="prev">Fixed-size Arrays in C</a>, Up: <a href="Multi_002ddimensional-Array-Format.html" accesskey="u" rel="up">Multi-dimensional Array Format</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
<hr>
|
|
<span id="Dynamic-Arrays-in-C-1"></span><h4 class="subsection">3.2.4 Dynamic Arrays in C</h4>
|
|
|
|
<p>We recommend allocating most arrays dynamically, with
|
|
<code>fftw_malloc</code>. This isn’t too hard to do, although it is not as
|
|
straightforward for multi-dimensional arrays as it is for
|
|
one-dimensional arrays.
|
|
</p>
|
|
<p>Creating the array is simple: using a dynamic-allocation routine like
|
|
<code>fftw_malloc</code>, allocate an array big enough to store N
|
|
<code>fftw_complex</code> values (for a complex DFT), where N is the product
|
|
of the sizes of the array dimensions (i.e. the total number of complex
|
|
values in the array). For example, here is code to allocate a
|
|
5 × 12 × 27
|
|
rank-3 array:
|
|
<span id="index-fftw_005fmalloc-2"></span>
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example">fftw_complex *an_array;
|
|
an_array = (fftw_complex*) fftw_malloc(5*12*27 * sizeof(fftw_complex));
|
|
</pre></div>
|
|
|
|
<p>Accessing the array elements, however, is more tricky—you can’t
|
|
simply use multiple applications of the ‘<samp>[]</samp>’ operator like you
|
|
could for fixed-size arrays. Instead, you have to explicitly compute
|
|
the offset into the array using the formula given earlier for
|
|
row-major arrays. For example, to reference the <em>(i,j,k)</em>-th
|
|
element of the array allocated above, you would use the expression
|
|
<code>an_array[k + 27 * (j + 12 * i)]</code>.
|
|
</p>
|
|
<p>This pain can be alleviated somewhat by defining appropriate macros,
|
|
or, in C++, creating a class and overloading the ‘<samp>()</samp>’ operator.
|
|
The recent C99 standard provides a way to reinterpret the dynamic
|
|
array as a “variable-length” multi-dimensional array amenable to
|
|
‘<samp>[]</samp>’, but this feature is not yet widely supported by compilers.
|
|
<span id="index-C99"></span>
|
|
<span id="index-C_002b_002b-2"></span>
|
|
</p>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|