Are 2D arrays contiguous?

[Tristan Miller]

Greetings.

Are statically allocated two-dimensional arrays guaranteed to be
contiguous, or is it possible the compiler will allocate padding after
each row? Is the following code OK?

#include <string.h>

int main(void) {
char a[5][5];
memset(a, 'x', 25);
return 0;
}

Regards,
Tristan

--
_
_V.-o Tristan Miller [en,(fr,de,ia)] >< Space is limited
/ |`-' -=-=-=-=-=-=-=-=-=-=-=-=-=-=-= < In a haiku, so it's hard
(7_\\ http://www.nothingisreal.com/ >< To finish what you

[daniel]

Re: Are 2D arrays contiguous?

On Aug 15, 1:38 pm, Tristan Miller <psychon...@not hingisreal.com>
wrote:

Greetings.
>
Are statically allocated two-dimensional arrays guaranteed to be
contiguous, or is it possible the compiler will allocate padding after
each row?  Is the following code OK?
>
#include <string.h>
>
int main(void) {
  char a[5][5];
  memset(a, 'x', 25);
  return 0;
>
}
>
Regards,
Tristan
>
--
   _
  _V.-o  Tristan Miller [en,(fr,de,ia)]  ><  Space is limited
 / |`-'  -=-=-=-=-=-=-=-=-=-=-=-=-=-=-= < In a haiku, so it's hard
(7_\\    http://www.nothingisreal.com/  ><  To finish what you

As far as I know they are.

[pete]

Re: Are 2D arrays contiguous?

Tristan Miller wrote:

Greetings.
>
Are statically allocated two-dimensional arrays guaranteed to be
contiguous,

Yes.

or is it possible the compiler will allocate padding after
each row?

No.

Is the following code OK?

Yes.

#include <string.h>
>
int main(void) {
char a[5][5];
memset(a, 'x', 25);
return 0;
}

--
pete

[Keith Thompson]

Re: Are 2D arrays contiguous?

Tristan Miller <psychonaut@not hingisreal.comw rites:

Are statically allocated two-dimensional arrays guaranteed to be
contiguous, or is it possible the compiler will allocate padding after
each row? Is the following code OK?
>
#include <string.h>
>
int main(void) {
char a[5][5];
memset(a, 'x', 25);
return 0;
}

Yes, because you're treating the object as an array of characters.

On the other hand, this:

a[0][5] = 'y';

will probably set a[1][0] to 'y', but it's not guaranteed; strictly
speaking, it's undefined behavior.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
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