strange output 2D array c++

Question

Hi I am trying to initialize a 2D array using a constructor. But there is always a memeber of the resultant array being 48 (always located at graph[0][9]), when the size input is 9 or 10. Other sizes, i.e. 12, 13, ... , 20, don't have this problem. Please tell me what's has gone wrong. Thanks very much!

Do I need to assign values to each member and this has something to do with memory?

#include <iostream>

class Graph {
public:
    Graph(int s=10);
    void print_graph() const;
private:
    int **graph;
    int size;
};

// function to create a 2D array
Graph::Graph(int s)
{
    size = s;
    
    graph = new int* [size];
    for (int i = 0; i < size; i++) 
        graph[i] = new int [size];
}

void Graph::print_graph() const
{
    for (int i = 0; i < size; i++) 
    {
        for (int j = 0; j < size; j++)
            std::cout << graph[i][j] << " ";
        std::cout << std::endl;
    }
}


int main()
{
    Graph g(9);
    g.print_graph();
}

output:

0 0 0 0 0 0 0 0 48

0 0 0 0 0 0 0 0 0

Jonathan Stanley-Smith · Accepted Answer · 2021-11-13 21:06:01Z

1

Operator new initializes memory to zero

Since you are not initializing the array once it is created, it could have any value.

answered Nov 13, 2021 at 21:06

Jonathan Stanley-Smith

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