Big size static array required

Question

I want a big sized array in a program.

My code has a structure which contains 3 float type variables and I want a largely sized 3 dimensional arrays of this structure.
My code is giving the output for small sized arrays, but when I increase the size of the array, I get a stack overflow exception/error.

Please help.

How large is your array? If it doesn't fit on the stack, allocate it on the heap. — user703016, Jun 13 '12 at 17:16
Your stack is not very big, maybe on the order of 8-16 MB or so. Your compiler might have some options for increasing the stack size, but you really should just allocate the array either statically at global scope, or dynamically on the heap. — Adam Rosenfield, Jun 13 '12 at 17:17
float d[15][15][15][15][15]; this is 5 dimensional array i need it. what is heap ? — Karan Arora, Jun 13 '12 at 17:18
If you really need all of those dimensions, I'd wrap it into a 1D vector. — chris, Jun 13 '12 at 17:20
'Create it on the heap' means you've to use the 'new' keyword to allocate the memory for the array. — Vite Falcon, Jun 13 '12 at 17:20
add the new operater to allocate to the heap. Just remember to delete it later — Brandon Kreisel, Jun 13 '12 at 17:20
@KaranArora [This](http://stackoverflow.com/questions/79923/what-and-where-are-the-stack-and-heap) is a good explanation for you. — Eitan T, Jun 13 '12 at 17:20
at first: i'm wondering what is the reason for using floats to layout a multidimensional array, as indices sure are of uint type. can you give an example what the values of those floats may be? do you need a 1.21212 x 6.23454 x 195.2322 array? shall the dimensions exceed MAX_INT? — Mare Infinitus, Jun 13 '12 at 17:48
@captain obvlious: perhaps he is in need of even a bigger float ;) — Mare Infinitus, Jun 13 '12 at 17:50

rubber boots · Answer 1 · 2012-06-13T17:34:43.037

3

Instead of

int main() {
   float array[N][N][N][N][N];
   ...

write

float array[N][N][N][N][N];

int main() {
   ...

Alternatively, write:

int main() {
   static float array[N][N][N][N][N];
   ...

BTW: my default setup in VC10/Win32 allows stack allocation up to N=12, which means ~ 990KB.

regards

rbo

edited Jun 13 '12 at 17:34

answered Jun 13 '12 at 17:22

rubber boots

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yes this is working. you can also increase the value of N by changing the memory reserved for stack. Its 1Mb by default. – Karan Arora Jun 13 '12 at 19:24

chris · Answer 2 · 2012-06-13T17:52:17.980

2

The made-for solution here is std::vector. It allocates memory on the heap, which is much larger than the stack, and can change its size without much extra effort at all.

typedef std::vector<float> vec;
typedef std::vector<vec> vec2D;
typedef std::vector<vec2D> vec3D;
typedef std::vector<vec3D> vec4D;
typedef std::vector<vec4D> vec5D;

vec5D d (15, vec4D (15, vec3D (15, vec2D (15, vec (15)))));
//use as you would a normal array for the most part

Of course having a 5D array (as mentioned "needed" in the comments) isn't something you particularly want. I recommend you make a Matrix class of sorts that has an underlying 1D vector instead.

Even better, rethink your design. There's rarely a time when you actually do need a highly multidimensional array such as that one.

edited Jun 13 '12 at 17:52

answered Jun 13 '12 at 17:32

chris

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The part about std::array is not true - the memory is not allocated dynamically. – jrok Jun 13 '12 at 17:42
@jrok, I could've sworn I've seen/had this discussion, and it was on the heap. I'll have to find it. – chris Jun 13 '12 at 17:43
Thanks for the information on the allocating memory on heap. Actually have 1 array of volume elements which is 3D , and a surface element which is 2D , and I need a distance between the 2. – Karan Arora Jun 13 '12 at 17:43
@jrok, Ah, yes, that wasn't `std::array`. Let me fix that then. – chris Jun 13 '12 at 17:44
And i think 5D array is best suited for it, bcoz i can recall a particular distance easily, BTW now the code is working, i do it by changing the stack size and global allocation – Karan Arora Jun 13 '12 at 17:45

score 1 · Answer 3 · answered Jun 13 '12 at 17:21

1

In addition to allocating it on the heap, you could simply try to reserve a bigger stack, using /F or /STACK option, or in project properties:

enter image description here

answered Jun 13 '12 at 17:21

Branko Dimitrijevic

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Come on guys, you don't give a knife to a baby here. Have him choose a better solution. – Michael Dorgan Jun 13 '12 at 17:22

score 0 · Answer 4 · answered Jun 13 '12 at 17:20

0

I don't know if you need to, but if you want, you may change the default stack size with linker options, for example in Visual Studio go "Properties - Configuration Properties - Linker - System - Stack Reserve Size".

answered Jun 13 '12 at 17:20

JustSomeGuy

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No - this is not the solution. Either malloc it or make it a global. Better yet, use a better data structure :) – Michael Dorgan Jun 13 '12 at 17:21
@MichaelDorgan Windows differentiate between reserving and committing the memory, so reserving enough stack space in advance may not be as wasteful as may seem at the first glance. – Branko Dimitrijevic Jun 13 '12 at 17:23
He wanted stack - he gets stack :) – JustSomeGuy Jun 13 '12 at 17:28

Big size static array required

4 Answers4