Chris@19: Previous: Dynamic Arrays in C, Chris@19: Up: Multi-dimensional Array Format Chris@19:
A different method for allocating multi-dimensional arrays in C is Chris@19: often suggested that is incompatible with FFTW: using it will Chris@19: cause FFTW to die a painful death. We discuss the technique here, Chris@19: however, because it is so commonly known and used. This method is to Chris@19: create arrays of pointers of arrays of pointers of ...etcetera. Chris@19: For example, the analogue in this method to the example above is: Chris@19: Chris@19:
int i,j;
Chris@19: fftw_complex ***a_bad_array; /* another way to make a 5x12x27 array */
Chris@19:
Chris@19: a_bad_array = (fftw_complex ***) malloc(5 * sizeof(fftw_complex **));
Chris@19: for (i = 0; i < 5; ++i) {
Chris@19: a_bad_array[i] =
Chris@19: (fftw_complex **) malloc(12 * sizeof(fftw_complex *));
Chris@19: for (j = 0; j < 12; ++j)
Chris@19: a_bad_array[i][j] =
Chris@19: (fftw_complex *) malloc(27 * sizeof(fftw_complex));
Chris@19: }
Chris@19:
Chris@19: As you can see, this sort of array is inconvenient to allocate (and
Chris@19: deallocate). On the other hand, it has the advantage that the
Chris@19: (i,j,k)-th element can be referenced simply by
Chris@19: a_bad_array[i][j][k].
Chris@19:
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If you like this technique and want to maximize convenience in accessing
Chris@19: the array, but still want to pass the array to FFTW, you can use a
Chris@19: hybrid method. Allocate the array as one contiguous block, but also
Chris@19: declare an array of arrays of pointers that point to appropriate places
Chris@19: in the block. That sort of trick is beyond the scope of this
Chris@19: documentation; for more information on multi-dimensional arrays in C,
Chris@19: see the comp.lang.c
Chris@19: FAQ.
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