Segmentation fault and core dumped when trying to declare a big array [duplicate]

Question

In my C program, when I try to assign this array value:

double sample[200000][2];

I get a segmentation fault error. But when I use:

double sample[20000][2]

it works!! Is there a limit to these index values?

Answer 1

It looks like you tried to reserve space for 200,000 x 2 = 400,000 double values, and each double is 8 bytes, so you tried to reserve around 3.2 Megabytes.

Even though your machine likely has a couple Gigs of memory, stack space is limited per-process and per-thread and may well be limited to 1 or 2 megabytes. So you cannot allocate 3 megs, and you crash.

To fix this, you want to change to dynamic memory, using malloc.
That will let you allocate from heap-space which is much more plentiful than stack-space.

To use malloc:

double (*sample) [200000];
s = malloc(sizeof(*sample) * 2); 
sample[0][0] = 0.0;
sample[1][199999] = 9.9;