I'm getting a segmentation fault error in my program, but it is unclear how

Question

From my understanding of segmentation faults, they occur when you try to access memory outside of the "space" of the program. My IDE says the exception occurs within in the first for loop where I perform the following operation: pi = w + i * i; I don't understand how I am accessing memory that I shouldn't access. The program is supposed to compute pi, up to a given amount of digits, it is not yet complete. I was testing what I have so far when the error occurred. The code follows:

/// computes the continued fraction, recursivley
int w = 1;
static long double pi = 0;
long double continued_fraction(int k, int i){

    for(int i = 1; i <= k; i++){
        pi += w + i * i;
        w += 2;
        pi /= continued_fraction(k, i++);
    }

    return pi;
}

/// continued fraction method to compute pi, up to a limit k
long double limit_fraction(int k){
    int i = 1;

    /// continued fraction method
    pi = 4 / continued_fraction(k, 1);

    return pi;
}

The function long double continued_fraction(int k, int i){ does not make a sense because its parameter i is not used. — Vlad from Moscow, Nov 15 '21 at 15:41
You didn't post a reproducable example, your program is not complete. Maybe k is just too large, and recursion goes too deep? I can't tell — Pepijn Kramer, Nov 15 '21 at 15:41
Walk through the program in a debugger and you will probably notice that the return value of `continued_fraction` is `0` for some value of `k`. — R Sahu, Nov 15 '21 at 15:41
https://ericlippert.com/2014/03/05/how-to-debug-small-programs/comment-page-2/ — R Sahu, Nov 15 '21 at 15:42
With a large enough `i`, `w + i * i` overflows. Consider `w + 1ll * i * i`. — chux - Reinstate Monica, Nov 15 '21 at 15:48
LoopGod, Why passed in `i` ignored with `long double continued_fraction(int k, int i){ for(int i = 1; i <= k; i++){`? — chux - Reinstate Monica, Nov 15 '21 at 15:49
@chux-ReinstateMonica count occurrences of `int i` in the fragment you posted. — n. m. could be an AI, Nov 15 '21 at 15:50
You mention an IDE that's pointing to the offending line. The IDE should have a way to to review the call stack---i.e., all the times `continued_fraction` was called, and the parameters used, to help diagnose the function's misbehavior leading to the crash. — Perette, Nov 15 '21 at 16:09
Recursion and mutating global variables is not a pleasant combination. Throwing a loop into that mix is usually a recipe for disaster. — molbdnilo, Nov 15 '21 at 16:36

score 3 · Accepted Answer · answered Nov 15 '21 at 15:51

Included code has infinitive recursion.

Lets call continued_fraction(1, 1). Then we enter for loop which redefines i and set it to 1 then first iteration when it does: continued_fraction(k, i++); it do: continued_fraction(1, 1) since post-increments provides old i.

This call is exactly same as first call, so recursion goes forever and you have stackoverflow - crash.

I'm getting a segmentation fault error in my program, but it is unclear how

1 Answers1