I was going through one of the threads. A program crashed because it had declared an array of 10^6 locally inside a function.

Reason being given was memory allocation failure on stack leads to crash.

when same array was declared globally, it worked well.(memory on heap saved it).

Now for the moment, let us suppose, stack grows downward and heap upwards.

We have:

---STACK---

-------------------

---HEAP----

Now , I believe that if there is failure in allocation on stack, it must fail on heap too.

So my question is: is there any limit on stack size? (crossing the limit caused the program to crash). Or am I missing something?

---

This all depends on what language and compiler you use. But programs compiled with for instance C or C++ allocate a fixed size stack at program startup. The size of the stack can usually be specified at compile time (on my particular compiler it default to 1 MB).

---

Yes, stack is always limited. In several languages/compilers you can set the requested size.

Usually default values (if not set manually) are about 1MB for current languages , which is enough unless you do something that usually isn't recommended (like you allocating huge arrays on the stack)

---

Contrary to all answers so far, on Linux with GCC (and I guess it is true for all modern POSIX operating systems), maximum stack size is a safety limit enforced by the operating system, that can be easily lifted.

I crafted a small program that calls recursively a function until at least 10 GB is allocated on stack, waits for input on the terminal, and then safely returns from all recursive calls up to main .

#include <stdio.h>
#include <string.h>
#include <sys/time.h>
#include <sys/resource.h>

void grow(unsigned cur_size)
{
    if(cur_size * sizeof(int) < 10ul*1024ul*1024ul*1024ul) {
        unsigned v[1000];
        v[0] = cur_size;
        for(unsigned i = 1; i < 1000; ++i) {
            v[i] = v[i-1] + 1;
        }

        grow(cur_size + 1000);

        for(unsigned i = 0; i < 1000; ++i) {
            if(v[i] != cur_size + i)
                puts("Error!");
        }
    } else {
        putchar('#');
        getchar();
    }
}

int main()
{
    struct rlimit l;
    l.rlim_max = RLIM_INFINITY;
    l.rlim_cur = RLIM_INFINITY;
    setrlimit(RLIMIT_STACK, &l);

    grow(0);
    putchar('#');
    getchar();
}

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