C multidimensional arrays, incompatible assignment

Question

Very specific problem, possibly due to my generally poor understanding of multidimensional arrays in C. I've got this code:

int io_pipes[NUM_IO_PROC][n][2][2];

for (int i = 0; i < n; ++i) {
    int pipes[NUM_IO_PROC][2][2];
    for (int j = 0; j < NUM_IO_PROC; ++j) pipes[j] = io_pipes[j][i];
}

There's some stuff missing, of course (like what happens to the pipes variable). Problem is that on line 5 there, I get a compiler error that say "incompatible type in assignment." I'd like it if the compiler gave me more information because as far as I know, pipes[j] and io_pipes[j][i] are both of type int[2][2].

I think more correctly pipes[j] and io_pipes[j][i] are both of type const int[2][2], which means you cannot assign to pipes[j]. — Brian L
– Brian L, Commented Oct 25, 2011 at 5:08
I went with the struct version, which allows me to do exactly what I wanted rather than the memcpy version below, and makes better sense overall. — meustrus
– meustrus, Commented Oct 26, 2011 at 20:58

Mateen Ulhaq · Accepted Answer · 2011-10-25 22:47:46Z

1

You cannot 'assign' arrays. (At least, what I think you're trying to do.)

You'll need to copy each element, one by one. Maybe you can use one of the existing library functions for this task?

for(int j = 0; j < NUM_IO_PROC; ++j)
    memcpy(&pipes[j], &io_pipes[j][i], sizeof pipes[j]);

edited Oct 25, 2011 at 22:47

answered Oct 25, 2011 at 4:41

Mateen Ulhaq

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1 Comment

caf Over a year ago

memcpy(&pipes[j], &io_pipes[j][i], sizeof pipes[j]); is probably clearer.

rmist · Accepted Answer · 2011-10-25 04:52:41Z

0

The arrays identifier is internally treadted as pointer to base address, but unlike pointers they cannot be assigned a new address value which you are trying to do in pipes[j] = io_pipes[j][i];

answered Oct 25, 2011 at 4:52

rmist

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