Segmentation fault in class

Question

#include <iostream>    
using namespace std;    
class Bucket{

    public:
        Bucket();
        void setN(int n);
        void setArrayb();
        void storeArray(int s, int cc, int **A);
        int showdata(int cc);
    private:
        int n_elements;
        int *b;

    };
    Bucket :: Bucket(){

        ;
    }
    void Bucket :: setN(int n)
        {
            n_elements = n;
        }

    void Bucket :: setArrayb(){

        int *b = new int [n_elements + 1];     
      }

    void Bucket :: storeArray(int s, int cc, int **A){


         cout << this -> n_elements;
        if(cc <= n_elements){
            this -> b[cc] = A[0][s];
        }

    }

    int Bucket :: showdata(int cc){
        return this -> b[cc];
    }

int main(){

    int n = 10;
    int** A = new int*[1];
    for (int i = 0 ; i < 1 ; i++){
        A[i] = new int [n + 1];
    }

    Bucket B[n + 1];
    A[0][3] = 6;

    int fb = 10;
    B[1].setN(fb) ;
    B[1].setArrayb();
    B[1].storeArray(3, 1, A);
    cout << B[1].showdata(1);
}

I'm trying to complete bucketsort with n bucket for A. n_element is the numbers of each bucket, after compiling, it's legal. But when I execute it, it cause segmentation fault.Can someone explain what happened in this code?

Using in linux environment by cygwin.

score 3 · Accepted Answer · answered Jan 08 '19 at 06:07

Your problem is caused by your misunderstanding of what the following line does in setArrayb.

int *b = new int [n_elements + 1];

It initializes a function local variable b.
It does not do anything to the member variable of the same name.
It leaks memory.

When you access the elements of the member variable b in storeArray, you access an uninitialized pointer, which causes undefined behavior.

Change that line to

b = new int [n_elements + 1];

Unless there is a need for you to manage dynamically allocated memory in your code, change your class to use std::vector<int>.

If you must manage your own memory, please follow The Rule of Three.

score 1 · Answer 2 · edited Jan 08 '19 at 06:07

1

in this section

 void Bucket :: setArrayb(){

    int *b = new int [n_elements + 1];     
  }

you should write b = new int [n_elements + 1];

edited Jan 08 '19 at 06:07

P.W

26,289
6
39
76

answered Jan 08 '19 at 06:03

samini

195
11

score 0 · Answer 3 · answered Jan 08 '19 at 06:06

0

void Bucket :: setArrayb(){
    int *b = new int [n_elements + 1];     
}

It allocates memory and stores pointer to it into local variable b, not this->b.

answered Jan 08 '19 at 06:06

273K

29,503
10
41
64

Segmentation fault in class

3 Answers3