Initialize a multdimensional array in C similar to Fortran

Question

I've written a small test case program in FORTRAN 90 which initializes a 3d array in slices. Can this same behavior be easily replicated in C?

  program fortranEngine

  real(4) , dimension(10,10) :: tmp
  real(4) , dimension(10,10,3) :: p    

  tmp = RESHAPE( [  0.973, 1.053, 0,     0,     0,     0,     0,     0,     0,     0, &
                    1.053, 1.080, 0,     0,     0,     0,     0,     0,     0,     0, &
                    1.010, 0.408, 0.442, 0,     0,     0,     0,     0,     0,     0, &
                    1.119, 0.900, 0.399, 0.762, 0,     0,     0,     0,     0,     0, &
                    1.211, 0.975, 0.845, 0.952, 1.105, 0,     0,     0,     0,     0, &
                    1.248, 1.016, 0.485, 0.000, 0.000, 1.110, 0,     0,     0,     0, &
                    1.225, 1.123, 1.056, 0.000, 0.000, 0.949, 0.832, 0,     0,     0, &
                    1.138, 1.232, 1.089, 1.050, 0.930, 0.402, 0.789, 0.774, 0,     0, &
                    1.149, 1.406, 1.201, 1.052, 0.416, 0.878, 0.896, 0.431, 1.144, 0, &
                    1.351, 1.255, 1.290, 1.358, 1.240, 1.228, 1.257, 1.140, 1.123, 1.228] &
                    , [10,10] )    

    p(:,:,1) = tmp    

    ...

    end program fortranEngine

Why bother replicating this in C ? Just call the Fortran routine from your C program. — High Performance Mark, Mar 14 '13 at 13:46
Try [this][1], seems pretty straightforward. [1]: http://stackoverflow.com/questions/2178909/how-to-initialize-3d-array-in-c — Erica Xu, Mar 14 '13 at 13:48
As always, real(4) may not do do thing You maybe think it does. In particular it is not the equivalent to real*4 — Vladimir F Героям слава, Mar 14 '13 at 14:22

score 2 · Answer 1 · answered Mar 14 '13 at 13:56

You can more or less do it in C99 or C2011, but it isn't as convenient as in Fortran. Beware initialization order; Fortran does it in one order (column-major) and C does it in the other (row-major). Ignoring that, you can do:

float tmp[10][10] =
{
    { 0.973, 1.053, 0,     0,     0,     0,     0,     0,     0,     0,    },
    { 1.053, 1.080, 0,     0,     0,     0,     0,     0,     0,     0,    },
    { 1.010, 0.408, 0.442, 0,     0,     0,     0,     0,     0,     0,    },
    { 1.119, 0.900, 0.399, 0.762, 0,     0,     0,     0,     0,     0,    },
    { 1.211, 0.975, 0.845, 0.952, 1.105, 0,     0,     0,     0,     0,    },
    { 1.248, 1.016, 0.485, 0.000, 0.000, 1.110, 0,     0,     0,     0,    },
    { 1.225, 1.123, 1.056, 0.000, 0.000, 0.949, 0.832, 0,     0,     0,    },
    { 1.138, 1.232, 1.089, 1.050, 0.930, 0.402, 0.789, 0.774, 0,     0,    },
    { 1.149, 1.406, 1.201, 1.052, 0.416, 0.878, 0.896, 0.431, 1.144, 0,    },
    { 1.351, 1.255, 1.290, 1.358, 1.240, 1.228, 1.257, 1.140, 1.123, 1.228 },
};
float p[3][10][10];    

for (int i = 0; i < 3; i++)
    memmove(p[i], tmp, sizeof(tmp));

Note that I moved the dimension [3] from the end of the declaration to the start of the declaration, though. The other way around would not make much sense in C. So, the notation is more or less available, but details of storage management make it less than obvious how to achieve exactly what you want.

score 1 · Answer 2 · answered Mar 14 '13 at 13:49

1

Is this easy enough?

for(int i = 0 ; i < 10 ; ++i) 
    for(int j = 0 ; j < 10 ; ++j )
        p[0][i][j] = tmp[i][j] ;

answered Mar 14 '13 at 13:49

Theodore Norvell

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Alternatively, if you don't mind that tmp and p share space, you can declare `double (*p[3])[10][10] ;` and assign `p[0] = &(tmp[0][0]) ;`. However then the other two slices are represented by null pointers. – Theodore Norvell Mar 14 '13 at 13:52
These arrays of arrays are not really the same as Fortran 3D arrays. – Vladimir F Героям слава Mar 14 '13 at 13:55
@Vladimir F. If you mean the one in my comment, you are right. For my answer I assume `p` is declared as `double [3][10][10];`, which I think it analogous to the fortran. However, I haven't used fortran since f77 days, so perhaps something changed. – Theodore Norvell Mar 14 '13 at 14:02
For this simple case you are right, I did not check the declaration. But one does not usually stay with small statically allocated arrays. – Vladimir F Героям слава Mar 14 '13 at 14:21

Initialize a multdimensional array in C similar to Fortran

2 Answers2