Assigning vectors as instance variables

[azaiiez]

In my .hpp file, my class is a graphe
I have as follows

vector< vector< Arc * > * > _adjacences; // adjacency list 

in my .cpp file, I was able to change the list to a matrix and implement Floyd algorithm but I did it this way, I declared the matrices inside the function

void Graphe::plusCourtChemin( void ){

        std::vector<vector<int>> matrix(_adjacences.size(), vector<int>(_adjacences.size()));
        std::vector<vector<int>> shortPath(_adjacences.size(), vector<int>(_adjacences.size()));

// alot of code ... 

I want to use the resulted matrixes and assign them as instance variables after filling them.

vector< vector< Arc * > * > _adjacences; // adjacency list
vector<vector<int>> matrix;
vector<vector<int>> shortPath

I get segmentation fault

[Repeater]

So you create many many pointers to Arc objects.

Do you ever create any actual Arc objects for those pointers to point at?

[azaiiez]

yes those are created from an XML file

[Repeater]

They need to be created in your C++ code.

[azaiiez]

Already done in another cpp file bro

void
Graphe::ajouterArcs( int a_sommet1, int a_sommet2, int a_longueur, string a_nom )
{
    int tailleMinimum = a_sommet1 < a_sommet2 ? a_sommet2 : a_sommet1;
    while( _adjacences.size() <= tailleMinimum )
    {
        _adjacences.push_back( new vector< Arc * >() );
    }

    assert( 0 <= a_sommet1 && a_sommet1 < _adjacences.size() );
    assert( nullptr != _adjacences[a_sommet1] );
    _adjacences[a_sommet1]->push_back( new Arc( a_sommet2, a_longueur, a_nom ) );

    assert( 0 <= a_sommet2 && a_sommet2 < _adjacences.size() );
    assert( nullptr != _adjacences[a_sommet2] );
    _adjacences[a_sommet2]->push_back( new Arc( a_sommet1, a_longueur, a_nom ) );
}

[Repeater]

Well it's going wrong somewhere, because you're getting a segFault.

I would recommend you don't use pointers.

When it segFaults, which line of code does the crash indicate is trying to read/write bad memory?

[Repeater]

This function:

void
Graphe::ajouterArcs( int a_sommet1, int a_sommet2, int a_longueur, string a_nom )
{
    int tailleMinimum = a_sommet1 < a_sommet2 ? a_sommet2 : a_sommet1;
    while( _adjacences.size() <= tailleMinimum )
    {
        _adjacences.push_back( new vector< Arc * >() );
    }

    assert( 0 <= a_sommet1 && a_sommet1 < _adjacences.size() );
    assert( nullptr != _adjacences[a_sommet1] );
    _adjacences[a_sommet1]->push_back( new Arc( a_sommet2, a_longueur, a_nom ) );

    assert( 0 <= a_sommet2 && a_sommet2 < _adjacences.size() );
    assert( nullptr != _adjacences[a_sommet2] );
    _adjacences[a_sommet2]->push_back( new Arc( a_sommet1, a_longueur, a_nom ) );
}

This create 2 Arc objects. Two. Is that how many you expect?

[azaiiez]

as soon as i try to fill them in my cpp file :

for ( unsigned i = 0; i < _adjacences.size(); i++)
                for (unsigned j = 0; j < _adjacences.size(); j++){
                        shortPath[i][j] = SP[i][j];
                        matrix[i][j] = M[i][j];
                }

and these are in my hpp file.

vector< vector< Arc * > * > _adjacences; // adjacency list
vector<vector<int>> matrix;
vector<vector<int>> shortPath

[Repeater]

When do you set the sizes of matrix and shortPath?

vector<vector<int>> matrix;
vector<vector<int>> shortPath;

These are of size 0 upon creation.

[azaiiez]

I didn't set them, should I ? I thought they'll be filled when I assign the values in the function.

[Repeater]

Any vector, if you don't set a size, begins at size zero.

So matrix[i][j] is very bad.

matrix contains many vectors. Each vector begins at size zero.
matrix itself is a vector. It begins at size zero.

You must either set their size, or you can have the size increment automatically using push_back to add elements to the end of a vector.

[George P]

Your vectors will be filled with data when you push_back each element.
https://en.cppreference.com/w/cpp/container/vector/push_back

If your data is complicated to create -- a class for instance -- instead of creating a temporary to push back you can create in-place an element with emplace_back (requires C++11 or later):
https://en.cppreference.com/w/cpp/container/vector/emplace_back

If you want to add an element in another location other than the end of the std::vector you can use insert or emplace:
https://en.cppreference.com/w/cpp/container/vector/insert
https://en.cppreference.com/w/cpp/container/vector/emplace

Resizing a std::vector "on the fly," adding new elements, repeatedly can be an expensive operation. It is better to specify the size when you create your std::vector if possible.

Adding elements to a sized std::vector is a simple operation of modifying the elements using operator[] or the .at operator.

[againtry]

You must either set their size, or you can have the size increment automatically using push_back to add elements to the end of a vector.

@OP, and in that vein your constructor should be something like the following for a Matrix declaration like Matrix my_matrix(8,71);

// CONSTRUCTOR
Matrix::Matrix (int rows, int cols){
    m_no_rows = rows;
    m_no_cols = cols;
    m_value.resize(m_no_rows, std::vector<int>(m_no_cols, 0)); // <--
}