Big array gives segmentation error in C
I am really new to C, so I am sorry if this is a absolute beginner question, but I am getting a segmentation error when I am building large array, relevant bits of what I am doing is:
unsigned long long ust_limit;
unsigned long long arr_size;
/* ust_limit gets value around here ... */
arr_size = ((ust_limit + 1) / 2) - 1;
unsigned long long numbs[(int)arr_size];
This works for some values of ust_limit, but when it gets above approximately 4.000.000 a segmentation fault occurs. What I want is to detect a possible segfault and fail gracefully. How can I know which values would cause a segmentation fault. And, is this something platform dependant?
You are most likely getting a stack overflow, since you are creating a very large array on the stack. To avoid this, allocate the memory dynamically:
unsigned long long *numbs = malloc(arr_size * sizeof(unsigned long long));
Later, when you are finished with the array, free it again:
free(numbs);
You're consuming too much stack. The limit is platform dependent.
The exact limit depends on the OS. These limits can be changed to some extent on some operating systems .
For large amounts of memory, you should be using the head with malloc and/or calloc (and free ).
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