Btukfyl

I created a function which is supposed to to get a binary tree in argument, a filename in user input and inside that file print the binary tree in order to be later converted into a picture via graphviz.

The binary tree type provided is:

struct noeud_s;



typedef struct noeud_s noeud;



typedef noeud* arbre;



struct noeud_s{

  char* valeur;

  arbre gauche;

  arbre droit;

};

The 2 functions I created are:

void create_dot(arbre racine)

{

  FILE *f;

  char file_name[100];

  printf ("Nom du fichier a creer (Ajouter .dot a la fin): ");

  scanf ("%s", file_name);

  printf("Name: %sn", file_name);

  printf ("Creation du fichier dotn");

  f = fopen(file_name, "w");

  if (f == NULL)

  {

    printf("NULLn");

  }

  fprintf(f, "digigraph tree {n");

  write_to_dot(f, racine);

  fprintf(f, "}");

  fclose(f);

}



void write_to_dot(FILE *f, arbre racine)

{

  if (racine == NULL)

  {

    return;

  }

  if (racine != NULL)

  {

    fprintf(f, "%s -> %s [label = "non"]n", racine -> valeur, racine -> gauche -> valeur);

    fprintf(f, "%s -> %s [label = "oui"]n", racine -> valeur, racine -> droit -> valeur);

    write_to_dot(f, racine -> gauche);

    write_to_dot(f, racine -> droit);

  }

  return;

}

As far as debugging goes, I have deducted that my segmentation fault happens inside the write_to_dot function. But because I can't properly handle gdb, I would like you to help me find my segmentation fault and explain it please.

The code is printing out a binary tree. There is no code showing how nodes are constructed, but in typical binary trees, the leaf nodes have NULL left & right child-nodes (or gauche and droit as it were).

The function write_to_dot will fail at the first leaf-node (if not at the empty-side of an intermediate branch-node), because racine->gauche and racine->droit would be NULL, yet they are still de-referenced - racine->gauche->valeur without any checking.

While I don't have all the code, at least testing for this condition will solve one of the issues:

void write_to_dot ( FILE *f, arbre racine )

{

    if ( racine != NULL )

    {

        if (racine->gauche != NULL)

            fprintf ( f, "%s -> %s [label = "non"]n", racine->valeur, racine->gauche->valeur );

        else

            fprintf ( f, "%s -> NULL [label = "non"]n", racine->valeur );



        if (racine->droit != NULL)

            fprintf ( f, "%s -> %s [label = "oui"]n", racine->valeur, racine->droit->valeur );

        else

            fprintf ( f, "%s -> NULL [label = "oui"]n", racine->valeur );



        write_to_dot ( f, racine->gauche );

        write_to_dot ( f, racine->droit );

    }

}