|
Chris@10
|
1 <html lang="en">
|
|
Chris@10
|
2 <head>
|
|
Chris@10
|
3 <title>Dynamic Arrays in C-The Wrong Way - FFTW 3.3.3</title>
|
|
Chris@10
|
4 <meta http-equiv="Content-Type" content="text/html">
|
|
Chris@10
|
5 <meta name="description" content="FFTW 3.3.3">
|
|
Chris@10
|
6 <meta name="generator" content="makeinfo 4.13">
|
|
Chris@10
|
7 <link title="Top" rel="start" href="index.html#Top">
|
|
Chris@10
|
8 <link rel="up" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format" title="Multi-dimensional Array Format">
|
|
Chris@10
|
9 <link rel="prev" href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C" title="Dynamic Arrays in C">
|
|
Chris@10
|
10 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
|
Chris@10
|
11 <!--
|
|
Chris@10
|
12 This manual is for FFTW
|
|
Chris@10
|
13 (version 3.3.3, 25 November 2012).
|
|
Chris@10
|
14
|
|
Chris@10
|
15 Copyright (C) 2003 Matteo Frigo.
|
|
Chris@10
|
16
|
|
Chris@10
|
17 Copyright (C) 2003 Massachusetts Institute of Technology.
|
|
Chris@10
|
18
|
|
Chris@10
|
19 Permission is granted to make and distribute verbatim copies of
|
|
Chris@10
|
20 this manual provided the copyright notice and this permission
|
|
Chris@10
|
21 notice are preserved on all copies.
|
|
Chris@10
|
22
|
|
Chris@10
|
23 Permission is granted to copy and distribute modified versions of
|
|
Chris@10
|
24 this manual under the conditions for verbatim copying, provided
|
|
Chris@10
|
25 that the entire resulting derived work is distributed under the
|
|
Chris@10
|
26 terms of a permission notice identical to this one.
|
|
Chris@10
|
27
|
|
Chris@10
|
28 Permission is granted to copy and distribute translations of this
|
|
Chris@10
|
29 manual into another language, under the above conditions for
|
|
Chris@10
|
30 modified versions, except that this permission notice may be
|
|
Chris@10
|
31 stated in a translation approved by the Free Software Foundation.
|
|
Chris@10
|
32 -->
|
|
Chris@10
|
33 <meta http-equiv="Content-Style-Type" content="text/css">
|
|
Chris@10
|
34 <style type="text/css"><!--
|
|
Chris@10
|
35 pre.display { font-family:inherit }
|
|
Chris@10
|
36 pre.format { font-family:inherit }
|
|
Chris@10
|
37 pre.smalldisplay { font-family:inherit; font-size:smaller }
|
|
Chris@10
|
38 pre.smallformat { font-family:inherit; font-size:smaller }
|
|
Chris@10
|
39 pre.smallexample { font-size:smaller }
|
|
Chris@10
|
40 pre.smalllisp { font-size:smaller }
|
|
Chris@10
|
41 span.sc { font-variant:small-caps }
|
|
Chris@10
|
42 span.roman { font-family:serif; font-weight:normal; }
|
|
Chris@10
|
43 span.sansserif { font-family:sans-serif; font-weight:normal; }
|
|
Chris@10
|
44 --></style>
|
|
Chris@10
|
45 </head>
|
|
Chris@10
|
46 <body>
|
|
Chris@10
|
47 <div class="node">
|
|
Chris@10
|
48 <a name="Dynamic-Arrays-in-C-The-Wrong-Way"></a>
|
|
Chris@10
|
49 <a name="Dynamic-Arrays-in-C_002dThe-Wrong-Way"></a>
|
|
Chris@10
|
50 <p>
|
|
Chris@10
|
51 Previous: <a rel="previous" accesskey="p" href="Dynamic-Arrays-in-C.html#Dynamic-Arrays-in-C">Dynamic Arrays in C</a>,
|
|
Chris@10
|
52 Up: <a rel="up" accesskey="u" href="Multi_002ddimensional-Array-Format.html#Multi_002ddimensional-Array-Format">Multi-dimensional Array Format</a>
|
|
Chris@10
|
53 <hr>
|
|
Chris@10
|
54 </div>
|
|
Chris@10
|
55
|
|
Chris@10
|
56 <h4 class="subsection">3.2.5 Dynamic Arrays in C—The Wrong Way</h4>
|
|
Chris@10
|
57
|
|
Chris@10
|
58 <p>A different method for allocating multi-dimensional arrays in C is
|
|
Chris@10
|
59 often suggested that is incompatible with FFTW: <em>using it will
|
|
Chris@10
|
60 cause FFTW to die a painful death</em>. We discuss the technique here,
|
|
Chris@10
|
61 however, because it is so commonly known and used. This method is to
|
|
Chris@10
|
62 create arrays of pointers of arrays of pointers of <small class="dots">...</small>etcetera.
|
|
Chris@10
|
63 For example, the analogue in this method to the example above is:
|
|
Chris@10
|
64
|
|
Chris@10
|
65 <pre class="example"> int i,j;
|
|
Chris@10
|
66 fftw_complex ***a_bad_array; /* <span class="roman">another way to make a 5x12x27 array</span> */
|
|
Chris@10
|
67
|
|
Chris@10
|
68 a_bad_array = (fftw_complex ***) malloc(5 * sizeof(fftw_complex **));
|
|
Chris@10
|
69 for (i = 0; i < 5; ++i) {
|
|
Chris@10
|
70 a_bad_array[i] =
|
|
Chris@10
|
71 (fftw_complex **) malloc(12 * sizeof(fftw_complex *));
|
|
Chris@10
|
72 for (j = 0; j < 12; ++j)
|
|
Chris@10
|
73 a_bad_array[i][j] =
|
|
Chris@10
|
74 (fftw_complex *) malloc(27 * sizeof(fftw_complex));
|
|
Chris@10
|
75 }
|
|
Chris@10
|
76 </pre>
|
|
Chris@10
|
77 <p>As you can see, this sort of array is inconvenient to allocate (and
|
|
Chris@10
|
78 deallocate). On the other hand, it has the advantage that the
|
|
Chris@10
|
79 (i,j,k)-th element can be referenced simply by
|
|
Chris@10
|
80 <code>a_bad_array[i][j][k]</code>.
|
|
Chris@10
|
81
|
|
Chris@10
|
82 <p>If you like this technique and want to maximize convenience in accessing
|
|
Chris@10
|
83 the array, but still want to pass the array to FFTW, you can use a
|
|
Chris@10
|
84 hybrid method. Allocate the array as one contiguous block, but also
|
|
Chris@10
|
85 declare an array of arrays of pointers that point to appropriate places
|
|
Chris@10
|
86 in the block. That sort of trick is beyond the scope of this
|
|
Chris@10
|
87 documentation; for more information on multi-dimensional arrays in C,
|
|
Chris@10
|
88 see the <code>comp.lang.c</code>
|
|
Chris@10
|
89 <a href="http://c-faq.com/aryptr/dynmuldimary.html">FAQ</a>.
|
|
Chris@10
|
90
|
|
Chris@10
|
91 <!-- -->
|
|
Chris@10
|
92 </body></html>
|
|
Chris@10
|
93
|
