occasional *** stack smashing detected*** with c++

Question

I have following C++ code for bubble sort. This code compiles without any error, but when I re compile and run, I get

*** stack smashing detected ***: terminated

As a C++ newby I want to know,why do I get these occasional errors when it runs?

void bubbleSort(int eatenPanCakes[10],int arrSize){
 
    int temp=0;
    for(int i=0;i<arrSize-1;i++){
        for (int j = 0; j < arrSize-i; j++)
        {
            if (eatenPanCakes[j] > eatenPanCakes[j+1])
            {
                temp = eatenPanCakes[j+1];
                eatenPanCakes[j+1] = eatenPanCakes[j];
                eatenPanCakes[j] = temp;
            }
        }       
    }
}

Environment: g++ (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0

There is a bug in my code: for (int j = 0; j+1 < arrSize-i; j++) would be the right algorithm and that works without error.

Ref-1 , Ref-2

Answer 1

You program is accessing array beyond its size which is an undefined behavior. Check this for loop condition:

for (int j = 0; j < arrSize-i; j++)

[I believe, arrSize value is 10 as the type of eatenPanCakes array is int [10] ] .

when i is 0 , arrSize-i value is 10 and in last iteration when j value is 9 , this statement

if (eatenPanCakes[j] > eatenPanCakes[j+1])

access j+1 ^th element of eatenPanCakes array which is element at index 10 . Note that an array of size 10 will have valid index from 0 to 9 .
Instead, the condition in for loop should be

for (int j = 0; j < arrSize - i - 1; j++)
                                ^^^

because the j ^th element is compared with element ahead of it in the array.