sizeof(array) in C: segmentation fault [duplicate] - c

Question

This question already has answers here:
Getting a stack overflow exception when declaring a large array
(8 answers)
Closed 6 years ago.
Hi i get a weird segmentation fault from this code:
int main(void){
int array1[10000000];
int n = sizeof(array1);
printf("%d \n", n );
return 0;
}
However if i change
int array1[10000000];
to
int array1[1000000]; ( one less zero)
The program works and prints 4000000
I'm running it on Fedora 21(64bits)
Is this because there is a maximum size for array in C? Thank you in advance

Answer 1

int array1[10000000];
is too large for your stack and you overflow your stack whereas
int array1[1000000];
is large, but does not overflow your stack as the array fits in it.
Note that the size of the stack can vary on different systems and can be set to a particular size.
Methods to solve it:
Make the array static.
Make the array global.
Allocate memory on the heap using malloc from stdlib.h:
int *array1;
array1 = malloc(10000000 * sizeof(int));
if(array1 == NULL) /* If `malloc` failed to allocate memory */
{
fputs("Oops! `malloc` failed to allocate memory!\n", stderr);
exit(-1); /* Exit the program with a return value of `-1` ; Requires `stdlib.h` */
}
/* Use the array and after use, free it using */
free(array1);

Answer 2

An additional method to solve it is to increase stack size with setrlimit. Standard size is 8 MB, at least on my Linux.
#include <stdio.h>
#include <errno.h>
#include <sys/resource.h>
static int setstacksize(rlim_t stacksize)
{
struct rlimit rl;
int res;
if ((res = getrlimit(RLIMIT_STACK, &rl)) != 0) {
fprintf(stderr, "getrlimit result = %d, errno = %d\n", res, errno);
return res;
}
if (rl.rlim_cur >= stacksize) return res;
rl.rlim_cur = stacksize;
if ((res = setrlimit(RLIMIT_STACK, &rl)) != 0) {
fprintf(stderr, "setrlimit result = %d, errno = %d\n", res, errno);
}
return res;
}
static int func(void){
int array1[10000000];
int n = sizeof array1;
printf("%d\n", n);
return 0;
}
int main(void){
setstacksize(48 * 1024 * 1024);
func();
return 0;
}