Segmentation fault when trying to fill a vector as instance variable

Question

I want to make a filled matrix as an instance variable in my .hpp file but end up with seg fault.

I have a graphe class. In my .cpp file, i filled an adjacency matrix as follows

void Graphe::shortRoute( void ){
    std::vector<vector<int>> matrix(_adjacences.size(), vector<int>(_adjacences.size()));
    std::vector<vector<int>> shortPath(_adjacences.size(), vector<int>(_adjacences.size()));
    
    for (unsigned i = 0; i < _adjacences.size(); i++) {
                for (auto j : *_adjacences[i]) {
                        matrix[i][j->sommetArrive] = j->longueur;
                }
        } 
... more and more code to get a filled shortPath matrix.

I implemented Floyd algorithm and everything works perfectly here and I printed the matrix to check it, it's all good.

the resulted matrices matrix and shortPath I wanted to make as instance variables

I tried as follows THIS CAUSES SEG FAULT WHY ?

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 in my .hpp file I declared SP and M as follows:

class Graphe
{
private:
    vector< vector< Arc * > * > _adjacences;
    std::vector<vector<int>> M;
    std::vector<vector<int>> SP;
....

as soon as I launch the program, i get seg fault from that new addition

Arc is as follows:

class Arc
{
public:
    int sommetArrive;
    int longueur;
    string nom;

    Arc( int a_sommetArrive, int a_longueur, string a_nom );
    virtual ~Arc( void );

    friend ostream & operator <<( ostream &, Arc const & );
};

As soon as you introduced pointers, we need to see where, how, and when those pointers become initialized. — PaulMcKenzie
– PaulMcKenzie, Commented Aug 4, 2020 at 18:42
When you asked this a few hours ago, we asked you to present a minimal reproducible example so that we can actually help you. That still applies, even though you deleted the original question. Cheers — Asteroids With Wings
– Asteroids With Wings, Commented Aug 4, 2020 at 18:45
I didn't get what minimal example means, I can't make an example because my program reads values from an XML file and point to them that's why :( — KingAzaiez
– KingAzaiez, Commented Aug 4, 2020 at 18:46
I have 2 matrices filled with int, how can i make them as instance variables in my Graphe class ? that's my question — KingAzaiez
– KingAzaiez, Commented Aug 4, 2020 at 18:47
@KingAzaiez Not what you are asking about but this code 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]; } can be simplified to this shortPath = SP; matrix = M; You don't have to write loops to copy vectors, the whole vector can be copied in a single assignment. I have a suspicion this might even cure your problem. — john
– john, Commented Aug 4, 2020 at 19:13

john · Accepted Answer · 2020-08-05 05:10:07Z

1

Not what you are asking about but this code

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]; 
    }

can be simplified to this

 shortPath = SP; 
 matrix = M;

You don't have to write loops to copy vectors, the whole vector can be copied in a single assignment.

I have a suspicion this might even cure your problem. If so then the original problem was probably that the shortPath and matrix vectors are zero size, so the loop code is assigning to vector elements that don't exist. When you copy a vector using a single assignment the size of the vector you are copying to changes to match the size of the vector you are copying from.

answered Aug 5, 2020 at 5:10

john

88.3k5 gold badges61 silver badges95 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Segmentation fault when trying to fill a vector as instance variable

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related