Cannot declare square matrix with large rows/columns (1446) in ANSI C [duplicate]

Question

I'm trying to declare an square matrix but I'm getting segfaults with values bigger than 1446 for rows/columns. I've found this value doing an "manual binary search".

Here's a snippet of my code:

boolean matrix[vertex][vertex];
memset(matrix, 0, sizeof(matrizAdjacencia[0][0]) * vertex * vertex);

The original run was trying to declare 32768*32768 positions. But it failed and then I started fixing low values until I found this 1446 value. The code fails before memset();

The boolean type is just an

typedef enum {true, false} boolean;

When running the program with gdb attached, the error generated is:

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_PROTECTION_FAILURE at address: 0x00007fff5f3ff548
0x00007fff8e6a5fba in tzload ()

Thanks in advance,

enum variables are likely to correspond to int. Might have better luck with char (which can certainly hold all the values of that enum). 1446*1446*4 = over 8 megabytes. — luser droog
– luser droog, Commented Sep 16, 2013 at 11:23
Don't define your own bool type if possible, use stdbool.h instead . Your current type likely has true==0 and false==1 which WILL cause problems in the future. — user694733
– user694733, Commented Sep 16, 2013 at 11:35
I'm doing static allocation only due academic purposes. I know that dynamic allocation of memory is way better than this... Thanks for the stdbool.h tip. I will check this. — Vinícius Ferrão
– Vinícius Ferrão, Commented Sep 16, 2013 at 11:41

Sakthi Kumar · Accepted Answer · 2013-09-17 06:33:40Z

3

This is possibly due to the stack size limit in the system. See ulimit -s which in most systems of 8MB.

So, 1446 * 1446 * 4 is nearly 8MB since enum takes size of int. So, you are not able to allocate more than the allowed stack size. The actual needed memory is 32768 * 32768 * 4 is nearly 4GB. You can probably use a bitmap, since you are dealing with boolean which reduces the needed memory. First changing the int to char reduces to 4GB / 4 = 1GB and from char to bit field reduces to 1GB / 8 = 128MB

Prefer using malloc or calloc for larger chunks of memory.

edited Sep 17, 2013 at 6:33

answered Sep 16, 2013 at 11:29

Sakthi Kumar

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4 Comments

Vinícius Ferrão Over a year ago

This should be the problem. I can confirm that max stack size is 8MB in my OS X system. I'm only using static matrix due academic purposes. So I just need to use an bitmap to allocate this portion of data?

Sakthi Kumar Over a year ago

Yes probably a char[req_size]. And u can use malloc or calloc. And each char represents 8 values.

Vinícius Ferrão Over a year ago

Can you recommend some documentation about bitmap implementations? I've never used this approach.

Sakthi Kumar Over a year ago

Hope these SO questions help stackoverflow.com/questions/2384016/… stackoverflow.com/questions/47981/…

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