2D dynamic array

GeorgeGento (11)
Hello.I have a problem using the 2d dynamic array.Althought i dont see any fault the debugger shows segmentation fault when i'm trying to access the the array using the index1 and index2.Thanks in advance. 


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Graph::Graph()
{
    adjacencymatrix = new bool*[graphsize];
    for (int i = 0;i<graphsize;i++)
    {
        adjacencymatrix[i] = new bool[graphsize];
    }
    for(int i = 0;i<graphsize;i++)
    {
        for(int k = 0;k<graphsize;k++)
        {
            adjacencymatrix[i][k] = false;
            adjacencymatrix[k][i] = false;
        }
    }
    garray = new int[graphsize];
    for(int i=0;i<graphsize;i++)
        garray[i] = -1;
}

//Adds new edge
void Graph::AddEdge(int no1,int no2)
{
    if(vertices == 0)
    {
        int vertices2 = vertices;
        garray[vertices] = no1;
        vertices++;
        garray[vertices] = no2;
        adjacencymatrix[vertices2][vertices] = true;
        adjacencymatrix[vertices][vertices2] = true;
        adjacencymatrix[vertices2][vertices2] = true;
        adjacencymatrix[vertices][vertices] = true;
    }
    int index1 = -1;
    int index2 = -1;
    //Tries to find the indexes that the numbers are located
    for (int i = 0;i<=vertices;i++)
    {
        if(garray[i] == no1)
            index1 = i;
        if(garray[i] == no2)
            index2 = i;
    }
    //If the numbers aren't in the array we put them in
    if(index1 == -1)
    {
        index1 = vertices;
        garray[index1] = no1;
        adjacencymatrix[index1][index1] = true;
        vertices++;
    }
    if(index2 == -1)
    {
        index2 = vertices;
        garray[index2] = no2;
        adjacencymatrix[index2][index2] = true;
        vertices++;
    }
    adjacencymatrix[index1][index2] = true;
    adjacencymatrix[index2][index1] = true;
    edges++;
    if(vertices == graphsize)
    {
        Expand();
    }
Last edited on
dutch (2548)
I don't think you've provided enough information for us to find your segfault.

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#include <iostream>

template<typename T>
class Array2D {
    int rows_, cols_;
    T** m_;
public:
    Array2D(int rows, int cols) : rows_(rows), cols_(cols) {
        m_ = new T*[rows];
        m_[0] = new T[rows * cols];
        for (int i = 1; i < rows; ++i)
            m_[i] = m_[i - 1] + cols;
        clear();
    }
    ~Array2D() {
        delete[] m_[0];
        delete[] m_;
    }
    void clear() {
        for (int r = 0; r < rows_; ++r)
            for (int c = 0; c < cols_; ++c)
                m_[r][c] = T();
    }
    void print() {
        for (int r = 0; r < rows_; ++r) {
            for (int c = 0; c < cols_; ++c)
                std::cout << m_[r][c] << ' ';;
            std::cout << '\n';
        }
        std::cout << '\n';
    }
    int rows() { return rows_; }
    int cols() { return cols_; }
    T* operator[](size_t i) { return m_[i]; }
    const T* operator[](size_t i) const { return m_[i]; }
};

int main() {
    Array2D<bool> m(5, 5);
    m.print();
    m[2][3] = true;
    m.print();
}

GeorgeGento (11)
That's the code.


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class Graph
{
    public:
        Graph();
        void AddEdge(int no1,int no2);
        int GetVertices(){return (vertices-1);}
        int GetEdges(){return edges;}
        bool DeleteEdge(int no1,int no2);
    protected:

    private:
        int graphsize = 10;
        bool **adjacencymatrix;
        int *garray;
        int vertices = 0;
        int edges = 0;
        void Expand();
};


Graph::Graph()
{
    adjacencymatrix = new bool*[graphsize];
    for (int i = 0;i<graphsize;i++)
    {
        adjacencymatrix[i] = new bool[graphsize];
    }
    for(int i = 0;i<graphsize;i++)
    {
        for(int k = 0;k<graphsize;k++)
        {
            adjacencymatrix[i][k] = false;
            adjacencymatrix[k][i] = false;
        }
    }
    garray = new int[graphsize];
    for(int i=0;i<graphsize;i++)
        garray[i] = -1;
}

//Adds new edge
void Graph::AddEdge(int no1,int no2)
{
    if(vertices == 0)
    {
        int vertices2 = vertices;
        garray[vertices] = no1;
        vertices++;
        garray[vertices] = no2;
        adjacencymatrix[vertices2][vertices] = true;
        adjacencymatrix[vertices][vertices2] = true;
        adjacencymatrix[vertices2][vertices2] = true;
        adjacencymatrix[vertices][vertices] = true;
    }
    int index1 = -1;
    int index2 = -1;
    //Tries to find the indexes that the numbers are located
    for (int i = 0;i<=vertices;i++)
    {
        if(garray[i] == no1)
            index1 = i;
        if(garray[i] == no2)
            index2 = i;
    }
    //If the numbers aren't in the array we put them in
    if(index1 == -1)
    {
        index1 = vertices;
        garray[index1] = no1;
        adjacencymatrix[index1][index1] = true;
        vertices++;
    }
    if(index2 == -1)
    {
        index2 = vertices;
        garray[index2] = no2;
        adjacencymatrix[index2][index2] = true;
        vertices++;
    }
    adjacencymatrix[index1][index2] = true;
    adjacencymatrix[index2][index1] = true;
    edges++;
    if(vertices == graphsize)
    {
        Expand();
    }
}

//Expands the graphs size
void Graph::Expand()
{
    int oldgraphsize = graphsize;
    graphsize = graphsize + 100;
    bool **newadjacencymatrix = new bool*[graphsize];
    for (int i;i<oldgraphsize;i++)
    {
        newadjacencymatrix[i] = new bool[graphsize];
        for(int k;k<oldgraphsize;k++)
        {
            newadjacencymatrix[i][k] = adjacencymatrix[i][k];
            newadjacencymatrix[k][i] = adjacencymatrix[k][i];
        }
    }
    delete[] adjacencymatrix;
    adjacencymatrix = newadjacencymatrix;
    int *newgarray = new int[graphsize];
    for(int i=0;i<oldgraphsize;i++)
    {
        newgarray[i] = garray[i];
    }
    delete[] garray;
    garray = newgarray;


}

//Deletes the edge of the given numbers,if they exist
bool Graph::DeleteEdge(int no1,int no2)
{
    bool flag = false;
    int index1 = -1;
    int index2 = -1;
    //Tries to find the indexes that the numbers are located
    for (int i = 0;i<=vertices;i++)
    {
        if(garray[i] == no1)
            index1 = i;
        if(garray[i] == no2)
            index2 = i;
    }
    //If the numbers exist deletes the edge
    if((index1 != -1) && (index2 != -1))
    {
        adjacencymatrix[index1][index2] = false;
        adjacencymatrix[index2][index1] = false;
        flag = true;
    }
    return flag;

}
dutch (2548)
See anything wrong here?

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    for (int i;i<oldgraphsize;i++)
    {
        newadjacencymatrix[i] = new bool[graphsize];
        for(int k;k<oldgraphsize;k++)


Also you aren't deleting the rows of the old adjacentymatrix.
And you should have a destructor.

Also, this doesn't make much sense:

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    for(int i = 0;i<graphsize;i++)
    {
        for(int k = 0;k<graphsize;k++)
        {
            adjacencymatrix[i][k] = false;
            adjacencymatrix[k][i] = false;
        }
    }

It should just be

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    for(int i = 0;i<graphsize;i++)
        for(int k = 0;k<graphsize;k++)
            adjacencymatrix[i][k] = false;

You do a similar thing in Expand, except that there you are trying to access memory through uninitialized pointers!
Last edited on
GeorgeGento (11)
Since it's undirected graph shouldn't i make both false?Else that would be directed graph right?Also i changed it so that it deletes the rows too and i was planning to create a destructor.I still get the segmantation faults even after fixing all these.Also after a few tests
it seems like it works fine for 9 inserts but not for more
Last edited on
Niccolo (720)
@GeorgeGento, you'll have to post your current version of the code to proceed with us here.
GeorgeGento (11)
Well, i've fixed the code and now it works perfectly.Thanks a lot for the help.
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