C Linked Lists Can't insert

Question

i'm facing a error right now on C, using Visual Studio and working with Linked Lists for the first time, i'm trying to make the project a little more structed, and because of that i'm facing some challenges. The error that i'm facing is, when i try to insert an element at a linked list my progam just crashes and give me this error :

Exception generated at 0x500CC944 (ucrtbased.dll) in Lesson_LinkedLists.exe: 0xC0000005: access violation while writing to local 0xCDCDCDCD.

I'm confused with this error, because it really does not support me with enough information so i can search over the internet.

Here are my structs, memory alocation and insert function :

typedef struct Word
{
    char Text[Max_Letters];
}*pt_Word;

typedef struct Node_Element
{
    pt_Word Word_Data;
    struct Node_Element * Next_Node_Element;
}*pt_Node_Element;

typedef struct List
{
    char Language[2];
    int Number_Words_List;
    pt_Node_Element Header;
}*pt_List;

pt_List List_Dynamic_Memory();

pt_Node_Element Node_Dynamic_Memory();

void Insert_Element_Begin(pt_Node_Element Node_Element, pt_List List_Pointer);

int main()
{
    int option;
    pt_Node_Element Node;
    pt_List List;
    List = List_Dynamic_Memory();
    Node = Node_Dynamic_Memory();

    do
    {
        option = menu();
        switch (option)
        {
            case 1: 
            {
                printf("Diga-me uma palavra : \n");
                //  fflush(stdin);
                gets_s(Node->Word_Data->Text);
                Insert_Element_Begin(Node, List);
                break;
            }   
            case 2: 
            {
                Display_List(Node, List); break;
            }
        }
    } while (option != 0);
    //system("Pause");
}

pt_List List_Dynamic_Memory()
{
    pt_List List_Pointer;

    List_Pointer = (pt_List)malloc(sizeof(struct List));

    List_Pointer->Header = NULL;
    List_Pointer->Number_Words_List = 0;

    return List_Pointer;

};

pt_Node_Element Node_Dynamic_Memory()
{
    pt_Node_Element  Node_Pointer;

    Node_Pointer = (pt_Node_Element)malloc(sizeof(struct Node_Element));

    Node_Pointer->Next_Node_Element = NULL;

    return Node_Pointer;
};

void Insert_Element_Begin(pt_Node_Element Node_Element, pt_List List_Pointer)
{
    List_Pointer->Number_Words_List++;

    if (List_Pointer->Header == NULL)
    {
        List_Pointer->Header = Node_Element;
        Node_Element->Next_Node_Element = NULL;

        return;
    }

    Node_Element->Next_Node_Element = List_Pointer->Header;
    List_Pointer->Header = Node_Element;
};

I'm wondering if it's something related to memory alocation, i'm a beginer so i'm sorry if it's a stupid error. Thanks for the help in advance.

Unrelated, try not using typedefs to hide pointer types. In all but two specific cases (neither of which apply here), it does more harm than good, and makes the code *less* readable and maintainable. C programmers *want* to see those asterisks when pointers are being used; it's their calling card. Also, [don't cast malloc in C programs](https://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc) — WhozCraig, Apr 27 '18 at 18:12
(I think it is very related.) In `Node_Element` you have a pointer to `struct Word`. But in `Node_Dynamic_Memory` you never `malloc` it. So you pass an uninitialized pointer to `get_s`(). — 001, Apr 27 '18 at 18:14
In Node_Element , Word_Data pointer is un initialized. I dont see memory being allocated. — NishanthSpShetty, Apr 27 '18 at 18:17
My problem is, how i'm suposed to initialize a string? Thanks for the answers by the way. Sorry i'm a noob. — Diogo Oliveira, Apr 27 '18 at 18:19
The man page for `char *gets_s(char *buffer, size_t sizeInCharacters);` shows you have a missing size argument in `gets_s(Node->Word_Data->Text);`. What did the compiler tell you about that? — Weather Vane, Apr 27 '18 at 18:22
@DiogoOliveira [Google it](https://stackoverflow.com/questions/4142745/initialize-a-string-in-c-to-empty-string) — Tormund Giantsbane, Apr 27 '18 at 18:23
I got no error on the compiler, when i run the code tho it gives me this Exception generated at 0x500CC944 (ucrtbased.dll) in Lesson_LinkedLists.exe: 0xC0000005: access violation while writing to local 0xCDCDCDCD. — Diogo Oliveira, Apr 27 '18 at 18:23

score 0 · Answer 1 · answered Apr 27 '18 at 18:38

As mentioned in the comments, you never allocate space for Word_Data. To fix that, you can use malloc():

pt_Node_Element Node_Dynamic_Memory()
{
    pt_Node_Element  Node_Pointer;

    Node_Pointer = (pt_Node_Element)malloc(sizeof(struct Node_Element));

    // Alloc mem for this too
    Node_Ponter->Word_Data = malloc(sizeof(struct Word));

    // You should also always check the value returned from malloc

    Node_Pointer->Next_Node_Element = NULL;

    return Node_Pointer;
};

It is also mentioned in the comments about hiding the fact that all those types are pointers. Doing that makes it easy to forget you are dealing with pointers. I advise against it.

Lastly, I see no reason Word_Data has to be a pointer. If it wasn't you would not have had this error:

struct Node_Element
{
    struct Word Word_Data;  // Does not need malloc
    struct Node_Element * Next_Node_Element;
};

And don't forget to free everything you malloc.

Thank you, i'm so gratefull for your time, i will try to work in the aspects that you point :). — Diogo Oliveira, Apr 27 '18 at 18:47

C Linked Lists Can't insert

1 Answers1