I have a 3dimensional array, how do I initialize it to a default value without having 3 loops.
dummy[4][4][1024]
, how do I initialize all the elements to 12?
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7What's wrong with 3 loops? It is the clearest way to initialize the array. Have pity on the reader.Art Swri– Art Swri2012-05-25 21:21:52 +00:00Commented May 25, 2012 at 21:21
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I agree, I was wondering if I can do all in oneshot, some compilers and in some other platforms we can directly initialize, was checking how does that work in Cuser1390048– user13900482012-05-25 21:30:23 +00:00Commented May 25, 2012 at 21:30
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possible duplicate of Fastest way to zero out a 2d array in C?CharlesB– CharlesB2012-05-29 08:34:25 +00:00Commented May 29, 2012 at 8:34
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3 Answers
Since the 3-d array is a contiguous block of memory, you can view it as a 1-d array
int i, *dummy2 = &dummy[0][0][0];
for(i = 0; i < 4*4*1024; ++i)
dummy2[i] = 12;
10 Comments
Kerrek SB
That's undefined behaviour.
Eitan T
@DanielFischer you need to declare
int i too :)Eitan T
BTW what's wrong with
int *dummy2 = (int *)dummy instead of &dummy[0][0][0]?
Daniel Fischer
Nothing. I just thought of taking the address first, @EitanT.
Fred Foo
@EitanT: explicit casts may hide bugs. This version will fail to compile when the base type of the array changes to, say,
long long. The version with the explicit cast still compiles but produces the wrong behavior. |
Come on guys - let's do it the simple way that always works:
for(int i = 0; i < 4; i++)
{
for(int j = 0; j < 4; j++)
{
for(int k = 0; k < 1024; k++)
{
dummy[i][j][k] = 12;
}
}
}
3 Comments
betabandido
I also like this one better. Especially since compilers may well optimize this code and make it as good as the most voted answer.
Daniel Fischer
@betabandido Even if not, the difference would be marginal. The only reason for treating it as a 1-d array was that the OP asked to do it "without having 3 loops".
betabandido
@DanielFischer that's a good one... my eyes skipped that part :)
The default initialization to all zeros is just that:
unsigned dummy[4][4][1024] = { 0 };
If you want to initialize particular elements (and all others to zero) do this
unsigned dummy[4][4][1024] = { { { 5 }, { 0, 4 } } };
and if your compiler knows C99 use designated initializers
unsigned dummy[4][4][1024] = { [3] = { [2] = { [0] = 7 }, [1] = { [2] = 3, [1] = 4 } } };
and if you really insist to use all 12, just repeat the 12 16384 times :)
