When I want for define to set 1000000, program in process crashed

Question

When I want to #define for SIZE 1.000.000 , my program crashed before it start main function, but when i #define for SIZE 100.000 it work. I have two arrays initialization in my program.

#define SIZE 1000000
char *baza_vocka[SIZE];    
    char b_vocka[SIZE];

EDIT: They are local variables.

I am curious. Do you define `char *baza_vocka[SIZE];` inside a function (`main` or any other function) or are they declared outside a function at global scope? — Michael Petch, Nov 03 '14 at 19:44
That observation is a bit soft. I can't imagine this would cause a problem in global scope. — Karoly Horvath, Nov 03 '14 at 19:45
With the edit that these are local variables you are encountering a stack overflow because the arrays are too big to fit on the stack. I wrote an answer to another *related* post with some extra information here: http://stackoverflow.com/questions/26077874/segmentation-fault-in-scanf — Michael Petch, Nov 03 '14 at 20:01

Anton K · Answer 1 · 2014-11-03T22:40:25.543

3

In case of 1M you're trying to allocate an array on the stack, which is bigger than the stack size. For such sizes you need to allocate the memory on heap.

For example:

int main()
{
    // allocation on the heap
    char **baza_vocka = malloc(sizeof(char*)*SIZE);
    char *b_vocka = malloc(sizeof(char)*SIZE);

    // working code
    baza_vocka[1] = 0x0;
    b_vocka[1] = 'a';

    // cleaning the heap
    free(b_vocka);
    free(baza_vocka);
}

edited Nov 03 '14 at 22:40

answered Nov 03 '14 at 19:46

Anton K

4,658
2
47
60

No, a 1M `static` array is ok. But a local array is not ok. – Basile Starynkevitch Nov 03 '14 at 19:48
Agreed, I just compiled and ran a program with a static array `char * ptr [4000000];` – Weather Vane Nov 03 '14 at 19:49
1

Whether it works or not will also depend on your compiler settings and what the stack size is and the total size of the array structure. – Michael Petch Nov 03 '14 at 19:50
But the example is with a heap-allocated array... And is C++, not C! – Basile Starynkevitch Nov 03 '14 at 19:50
@BasileStarynkevitch I think he meant a stack allocated array. Static arrays are defined in a special exe section and they don't need to be allocated. – Eldar Dordzhiev Nov 03 '14 at 19:51
@Eldar: I know that, but the answer still mentions "static array" – Basile Starynkevitch Nov 03 '14 at 19:51
@BasileStarynkevitch Sorry, I thought you were OP – Eldar Dordzhiev Nov 03 '14 at 19:52
My comment about whether it works or not was actually addressing the `No, a 1M static array is ok. But a local array is not ok` . It may be okay or it may not. But I think the point we are both making is that big objects on the stack are a bad idea because you will *run the risk* of an overflow – Michael Petch Nov 03 '14 at 20:10
In C, don't cast the result of malloc. – Étienne Nov 03 '14 at 20:39
@Étienne Oh, yeah. Fixed. – Anton K Nov 03 '14 at 22:41
Thanks for responding, but i have two question, 1. what is 1M , 2. what have been minding with (**) , what is that , (char **baza_vocka)? – lotoflaugh Nov 08 '14 at 20:18
1. 1M = 1'000'000 = one million, that was defined in SIZE macro and stated in the question, 2. (char **) is converting (void *) to pointer to pointer to char. If you like the answer, please mark it as answer. – Anton K Nov 09 '14 at 23:33

Basile Starynkevitch · Answer 2 · 2014-11-03T19:52:53.197

I guess that baza_vocka is a local variable, perhaps inside main

You are experimenting some stack overflow, .... Local call frames should usually be small (a few kilobytes) in your call stack

You should not have so big local variables. Allocate such big arrays in the heap using malloc or calloc. Don't forget to test that they are not failing. Read documentation of malloc(3), and don't forget to free such a heap allocated array. Beware of memory leaks & buffer overflows. Use valgrind if available.

On current desktops, stack space is a few megabytes, so you usually should limit each call frame to a few kilobytes (or a few dozens of kilobytes).

When I want for define to set 1000000, program in process crashed

2 Answers2

Linked