Segmentation fault error in C when trying to print to a file





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1















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.










share|improve this question


















  • 1





    You are dereferencing a null pointer here: fprintf(f, "%s -> %s [label = "non"]n", racine -> valeur, racine -> gauche -> valeur); -->> fprintf, "%s -> %s [label = "non"]n", racine->valeur, rachine->gauche ? racine->gauche->valeur" : "Jamais!" );

    – wildplasser
    Nov 22 '18 at 0:25













  • If you can run your program under gdb, you can enter commands like print racine, print racine->valeur, print racine->gauche, and so on. This will likely pinpoint the problem quickly. We can't do that because we have no idea how your code is calling create_dot. Likely the problem is in the value passed for racine and what it points to.

    – David Schwartz
    Nov 22 '18 at 0:27








  • 2





    "But because I can't properly handle gdb" - then this would be an excellent opportunity for you to learn how to properly handle gdb. "Teach a man to fish" and all that stuff.

    – paxdiablo
    Nov 22 '18 at 0:28






  • 1





    If I may, the typedef noeud* arbre; ... I would like to suggest that typedef-ing pointer types to another name just confuses things. Unless of course "arbre" just means "pointer-to"

    – Kingsley
    Nov 22 '18 at 0:34











  • @Kingsley I know that it's confusing but I have no choise. I was given that as a type definition and I can't change it

    – Sotiris Kettenis
    Nov 22 '18 at 1:01


















1















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.










share|improve this question


















  • 1





    You are dereferencing a null pointer here: fprintf(f, "%s -> %s [label = "non"]n", racine -> valeur, racine -> gauche -> valeur); -->> fprintf, "%s -> %s [label = "non"]n", racine->valeur, rachine->gauche ? racine->gauche->valeur" : "Jamais!" );

    – wildplasser
    Nov 22 '18 at 0:25













  • If you can run your program under gdb, you can enter commands like print racine, print racine->valeur, print racine->gauche, and so on. This will likely pinpoint the problem quickly. We can't do that because we have no idea how your code is calling create_dot. Likely the problem is in the value passed for racine and what it points to.

    – David Schwartz
    Nov 22 '18 at 0:27








  • 2





    "But because I can't properly handle gdb" - then this would be an excellent opportunity for you to learn how to properly handle gdb. "Teach a man to fish" and all that stuff.

    – paxdiablo
    Nov 22 '18 at 0:28






  • 1





    If I may, the typedef noeud* arbre; ... I would like to suggest that typedef-ing pointer types to another name just confuses things. Unless of course "arbre" just means "pointer-to"

    – Kingsley
    Nov 22 '18 at 0:34











  • @Kingsley I know that it's confusing but I have no choise. I was given that as a type definition and I can't change it

    – Sotiris Kettenis
    Nov 22 '18 at 1:01














1












1








1








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.










share|improve this question














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.







c segmentation-fault binary-tree






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Nov 22 '18 at 0:19









Sotiris KettenisSotiris Kettenis

212




212








  • 1





    You are dereferencing a null pointer here: fprintf(f, "%s -> %s [label = "non"]n", racine -> valeur, racine -> gauche -> valeur); -->> fprintf, "%s -> %s [label = "non"]n", racine->valeur, rachine->gauche ? racine->gauche->valeur" : "Jamais!" );

    – wildplasser
    Nov 22 '18 at 0:25













  • If you can run your program under gdb, you can enter commands like print racine, print racine->valeur, print racine->gauche, and so on. This will likely pinpoint the problem quickly. We can't do that because we have no idea how your code is calling create_dot. Likely the problem is in the value passed for racine and what it points to.

    – David Schwartz
    Nov 22 '18 at 0:27








  • 2





    "But because I can't properly handle gdb" - then this would be an excellent opportunity for you to learn how to properly handle gdb. "Teach a man to fish" and all that stuff.

    – paxdiablo
    Nov 22 '18 at 0:28






  • 1





    If I may, the typedef noeud* arbre; ... I would like to suggest that typedef-ing pointer types to another name just confuses things. Unless of course "arbre" just means "pointer-to"

    – Kingsley
    Nov 22 '18 at 0:34











  • @Kingsley I know that it's confusing but I have no choise. I was given that as a type definition and I can't change it

    – Sotiris Kettenis
    Nov 22 '18 at 1:01














  • 1





    You are dereferencing a null pointer here: fprintf(f, "%s -> %s [label = "non"]n", racine -> valeur, racine -> gauche -> valeur); -->> fprintf, "%s -> %s [label = "non"]n", racine->valeur, rachine->gauche ? racine->gauche->valeur" : "Jamais!" );

    – wildplasser
    Nov 22 '18 at 0:25













  • If you can run your program under gdb, you can enter commands like print racine, print racine->valeur, print racine->gauche, and so on. This will likely pinpoint the problem quickly. We can't do that because we have no idea how your code is calling create_dot. Likely the problem is in the value passed for racine and what it points to.

    – David Schwartz
    Nov 22 '18 at 0:27








  • 2





    "But because I can't properly handle gdb" - then this would be an excellent opportunity for you to learn how to properly handle gdb. "Teach a man to fish" and all that stuff.

    – paxdiablo
    Nov 22 '18 at 0:28






  • 1





    If I may, the typedef noeud* arbre; ... I would like to suggest that typedef-ing pointer types to another name just confuses things. Unless of course "arbre" just means "pointer-to"

    – Kingsley
    Nov 22 '18 at 0:34











  • @Kingsley I know that it's confusing but I have no choise. I was given that as a type definition and I can't change it

    – Sotiris Kettenis
    Nov 22 '18 at 1:01








1




1





You are dereferencing a null pointer here: fprintf(f, "%s -> %s [label = "non"]n", racine -> valeur, racine -> gauche -> valeur); -->> fprintf, "%s -> %s [label = "non"]n", racine->valeur, rachine->gauche ? racine->gauche->valeur" : "Jamais!" );

– wildplasser
Nov 22 '18 at 0:25







You are dereferencing a null pointer here: fprintf(f, "%s -> %s [label = "non"]n", racine -> valeur, racine -> gauche -> valeur); -->> fprintf, "%s -> %s [label = "non"]n", racine->valeur, rachine->gauche ? racine->gauche->valeur" : "Jamais!" );

– wildplasser
Nov 22 '18 at 0:25















If you can run your program under gdb, you can enter commands like print racine, print racine->valeur, print racine->gauche, and so on. This will likely pinpoint the problem quickly. We can't do that because we have no idea how your code is calling create_dot. Likely the problem is in the value passed for racine and what it points to.

– David Schwartz
Nov 22 '18 at 0:27







If you can run your program under gdb, you can enter commands like print racine, print racine->valeur, print racine->gauche, and so on. This will likely pinpoint the problem quickly. We can't do that because we have no idea how your code is calling create_dot. Likely the problem is in the value passed for racine and what it points to.

– David Schwartz
Nov 22 '18 at 0:27






2




2





"But because I can't properly handle gdb" - then this would be an excellent opportunity for you to learn how to properly handle gdb. "Teach a man to fish" and all that stuff.

– paxdiablo
Nov 22 '18 at 0:28





"But because I can't properly handle gdb" - then this would be an excellent opportunity for you to learn how to properly handle gdb. "Teach a man to fish" and all that stuff.

– paxdiablo
Nov 22 '18 at 0:28




1




1





If I may, the typedef noeud* arbre; ... I would like to suggest that typedef-ing pointer types to another name just confuses things. Unless of course "arbre" just means "pointer-to"

– Kingsley
Nov 22 '18 at 0:34





If I may, the typedef noeud* arbre; ... I would like to suggest that typedef-ing pointer types to another name just confuses things. Unless of course "arbre" just means "pointer-to"

– Kingsley
Nov 22 '18 at 0:34













@Kingsley I know that it's confusing but I have no choise. I was given that as a type definition and I can't change it

– Sotiris Kettenis
Nov 22 '18 at 1:01





@Kingsley I know that it's confusing but I have no choise. I was given that as a type definition and I can't change it

– Sotiris Kettenis
Nov 22 '18 at 1:01












1 Answer
1






active

oldest

votes


















2














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 );
}
}





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    1 Answer
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    1 Answer
    1






    active

    oldest

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    active

    oldest

    votes






    active

    oldest

    votes









    2














    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 );
    }
    }





    share|improve this answer






























      2














      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 );
      }
      }





      share|improve this answer




























        2












        2








        2







        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 );
        }
        }





        share|improve this answer















        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 );
        }
        }






        share|improve this answer














        share|improve this answer



        share|improve this answer








        edited Nov 22 '18 at 1:05

























        answered Nov 22 '18 at 0:53









        KingsleyKingsley

        3,55731428




        3,55731428
































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