Why C compiler says * stack smashing detected *: terminated

Question

What is problem with my code, that it shows "stack smashing detected" Problem Statement: Given an array, we have to find the smallest element in the array.

#include<stdio.h>
int main(){
    int arr[20],i,j,c,x,num;
    scanf("%d",&num);
    for(x=0;x<num;x++){
        scanf("%d",&arr[x]);
    }
    for(i=0;i<sizeof(arr)-1;i++){
        if(arr[i]>arr[i+1]){
            c=arr[i];
            arr[i]=arr[i+1];
            arr[i+1]=c;
        }
    }
    printf("%d",*(arr+0));
    return 0;
}

Welcome to Stack Overflow. Please read [ask] and https://ericlippert.com/2014/03/05/how-to-debug-small-programs/, and try to trace through the logic of the code. Hint: what do you expect to be the result of `sizeof(arr)`? What *is* the result? Do you understand why? — Karl Knechtel, Jun 08 '22 at 17:42
Questions seeking debugging help should generally provide a [mre] of the problem, which includes the exact input required to reproduce the problem. — Andreas Wenzel, Jun 08 '22 at 18:10
Oh, and it is not the _compiler_ but your _program_ that emits that message. — the busybee, Jun 08 '22 at 18:27

score 0 · Answer 1 · answered Jun 08 '22 at 17:43

0

If the user-provided value num is greater than 20, your code will write to memory off the end of the array arr. This is undefined behaviour, and likely to cause a crash.

answered Jun 08 '22 at 17:43

GKFX

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score 0 · Answer 2 · answered Jun 08 '22 at 17:47

0

Two problems:

(1) int arr[20] can only hold twenty values, but you let the user put in any number.

(2) sizeof(arr) gives you the size in bytes, not the number of elements.

The compiler is able to detect one or both of these problems, and give you an error message telling you.

answered Jun 08 '22 at 17:47

CoffeeTableEspresso

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I'm aware of first one, but the second point cleared my doubt. Thankyou... – Nitin Pandey Jun 08 '22 at 17:54

Why C compiler says *** stack smashing detected ***: terminated

2 Answers2

Why C compiler says * stack smashing detected *: terminated