Question

#include <stdio.h>
#include <iostream>
#include <stdlib.h>
#include <string.h>

using namespace std;

void multiplier_matrice_vecteur (char * v0, char * A, int N)
{
    int i,j,k;
    char somme;

    for (i = 0; i < N; i++) //On fait N calculs car c'est une matrice 1xN
    {
        //On fait N additions + multiplications
        somme = 0;
        for (j = 0; j < N; j++)
        {
            somme += v0[i] * A[i * N + j];
        }
        v0[i] = somme;
    }
}

int main(void)
{
    bool premiereLignefaite = false;
    //Lire le fichier
    FILE * graphe = fopen("graphe.txt", "r");
    //Fichier de sortie
    FILE * resultat = fopen("resultat.txt", "w");
    int nbr1, nbr2;
    int N;
    char *matrice; //pointeur vers la matrice d'adjacence

    //Ligne lue
    static char ligne[50];

    while (fgets(ligne, 50, graphe) != NULL) //retourne 0 quand on a end-of-file
    {
        //La premiere ligne est différente
        if (premiereLignefaite == false) {
            //Initialiser une matrice d'adjacence NxN
            sscanf(ligne, "%d %d", &nbr1, &nbr2);
            N = nbr1;
            matrice =  new char(nbr1 * nbr1); //Memoire dynamique pour la matrice dadjacence n x n
            memset(matrice, 0, nbr1*nbr1);
            premiereLignefaite = true;
            continue;
        }
        //On construit notre matrice d'adjacence
        sscanf(ligne, "%d %d", &nbr1, &nbr2);
        matrice[nbr1 * N + nbr2    ] = 1;
    }

    printf("Matrice d'adjacence %dx%d : \n", N, N);
    //Affichage de la matrice d'adjacence
    for (int i = 0; i < N; i++)
    {
        for (int j = 0; j < N; j++)
        {
            printf("%c ", matrice[i * N + j] + '0');
        }
        printf("\n");
    }

    //Application de l'algo étapes par étapes
    double tolerance = 0.00001; //Niveau de tolérance de la méthode
    char * v0; //vecteur propre taille N
    char * v; //vecteur tampon
    int valeur; //valeur propre
    int valeur_tamp; //valeur propre tampon

    //Initialiser v0
    v0 = new char(N);
    memset(v0, 1, N);

    //Initialiser A (déja fait)
    //Initialiser tolérance (deja fait)

    valeur = 0;
    while (1)
    {

        valeur_tamp = valeur;
        //Multiplication du vecteur par la matrice
        multiplier_matrice_vecteur(v0, matrice, N);
    }

    //Désallocation de la mémoire
    delete matrice;

    //Fermeture des fichiers etc
    fclose(graphe);
    fclose(resultat);

    return 0;
}

So this is the program I have been coding since 2PM on my laptop. I am using Visual Studio 2008 and Windows 7 64 bits. I’m coding, everything’s going fine. When I try to test my program, the line :

v0 = new char(N);

Gives me an exception. I try getting my memory with malloc and calloc and what do I get? A null pointer!! I have 4 gigs of ram on my machine and there’s no way I can’t get 9 bytes of memory here. I don’t understand this at all.

For those who have Visual Studio 2008 and want to test under the same environnement, you will need the file graphe.txt, here’s that file :

9 20
0 1
0 2
1 0
1 2
1 3
1 5
2 0
2 1
2 3
3 1
3 2
3 4
4 3
5 1
5 6
5 7
6 5
6 8
7 5
8 6

I thought that this was a machine problem, So I come back home, I try the program on my desktop computer and it’s the same problem…

I’d have to try on GCC but since I’m always using Visual C++ I want to solve the problem on this environment…

EDIT: The following code now works. For some reason, if you use parentheses in the first new, it will work, but the next time you use new, it won’t work!!
If I put both new allocations with [] syntax, it works. If I put the first new allocation with [] and the second one with (), it also works. WEIRD. Anyways, i’ll be using [] from now on… Thank you all.

Answer 1

You should use

matrice = new char[nbr1 * nbr1];

and remember to free with

delete[] matrice;