Segmentation fault (Core Dumped) C++ Beginner

Question

So, I am new to C++. I've researched Segmentation Fault (core dumped), memory allocation, and new/delete although I am having trouble understanding the concepts. I do believe my problem lies with memory allocation though and that's why I thought "delete" would have solved my problem. May someone please push me in the right direction?

Input

#include <iostream>
#include <string>

using namespace std;

struct CandyBar
{
    string name;
    double weight;
    int calories;
} ;

int main()
{
    CandyBar* backpack = new CandyBar[3];
    backpack[0] = {"Choco Chalk", 5.1, 725};
    backpack[1] = {"Twisty String", 1.8, 300};
    backpack[2] = {"Gummy Nums", 4.4, 475};

    cout << "Name\t\tWeight\tCalories" << endl << endl;
    for (int x = 0; x < 4; x++)
    {
        cout << backpack[x].name << "\t" << backpack[x].weight << "\t" << backpack[x].calories << endl;
    }

    delete backpack;

    return 0;
}

Output

Name            Weight    Calories

Choco Chalk     5.1       725
Twisty String   1.8       300
Gummy Nums      4.4       475
(Segmentation fault) core dumped

@Evert I believe you are suggesting I make it `x < 3` and it resulted in an error having to do with `munmap_chunk(): invalid pointer`. — Voozio, Feb 22 '16 at 05:30
Compile with all warnings & debug info (e.g. `g++ -Wall -Wextra -g`) then **use the debugger** (`gdb`) — Basile Starynkevitch, Feb 22 '16 at 05:39

score 2 · Accepted Answer · edited May 23 '17 at 11:45

I see two bugs:

Your loop for (x = 0; x < 4; x++) will iterate through x values 0, 1, 2, 3. However, since you allocated backpack with new Candybar[3], backpack points to only enough memory to hold 3 CandyBars, namely backpack[0], backpack[1], backpack[2]. As it stands, on its fourth time through, your loop will attempt to access backpack[3], which is off the end of the array.
When you allocate memory with new[] (as you did since you allocated an array of CandyBar), you have to deallocate it with delete[], not just plain delete. See delete vs delete[] operators in C++.

When I changed your loop exit condition to x < 3 and your deallocation to delete[] backpack;, the program worked for me.

@Voozio Memo: if your array is of size `n` use `x < n` (strictly less than array size) as a loop condition. — Ivan Aksamentov - Drop, Feb 22 '16 at 06:25

Segmentation fault (Core Dumped) C++ Beginner

1 Answers1