Limited recursion in C?

Question

I ran this program and it output

...

65088
65089
65090

and then it stopped. Windows 7 said a.exe stopped working. Here is the code:

#include <stdio.h>

void go(void);

main()
{
    go();
}

void go(void)
{
    static int i = 0;
    printf("%d\n", i++);
    go();
}

I think this program should keep on printing numbers indefinitely due to recursion, but it stops at 65090! The C code is compiled with gcc. Any ideas?

Answer 1

You are going to overflow the stack at some point because each call to go() must push a return address on the stack even though you pass no arguments to the function call. So every call to go() is taking up a pointer-sized block on the stack for that return address. Since the stack has a limited size, that means at some point you're going to run out of space. The C-language does not specify that a tail-call optimization should take place for circumstances like this, although some compilers (like gcc) do offer that option via optimization switches. But that would be something that is compiler-specific, and independent of the language specification.

Answer 2

It stops because it is overflowing the stack. Once you overflow the stack the results are undefined.

Answer 3

You cannot recurse infinitely on a machine with finite resources -- specifically, the stack. Each nested subroutine call required more stack space, and eventually you will run out.