How to add a structure to a linked list? in C

Question

I'm trying to add a frame to a linked list of such structures, but instead of adding a new structure to the list each time, the program adds nothing, can anyone tell me what the problem is? Or give me a better exercise method?

The structures:

typedef struct Frame
{
    char* name;
    int duration;
    char* path;

} Frame;


// Link (node) struct
typedef struct FrameNode
{
    Frame* frame;
    struct FrameNode* next;
} FrameNode;

The functions:

FrameNode* addFrame(Frame* frame)
{
    char name[100] = { 0 };
    char path[100] = { 0 };
    int dur = 0;
    Frame* p = (Frame*)malloc(sizeof(Frame));

    printf("*** Creating a new frame ***\n");
    printf("Please insert frame path:\n");
    fgets(path, 100, stdin);
    path[strcspn(path, "\n")] = 0;
    strcpy(p->path, path);

    printf("Please insert frame duration <in miliseconds>:\n");
    scanf("%d", &dur);
    getchar();
    p->duration = dur;

    printf("Please chooce a name for a new frame:\n");
    fgets(name, 100, stdin);
    name[strcspn(name, "\n")] = 0;
    strcpy(p->name, name);
    while (list != NULL)
    {
        if (strcmp(list->frame->name, p->name) == 0)
        {
            printf("The name is already taken, Please enter another name\n");
            fgets(name, 100, stdin);
            name[strcspn(name, "\n")] = 0;
            strcpy(p->name, name);
        }
        list = list->next;
    }
    free(p);
    return p;
}

FrameNode* insertAtEnd(FrameNode** list, Frame* fr)
{
    if (*list)
    {
        FrameNode* help = *list;
        FrameNode* tmp = (FrameNode*)malloc(sizeof(FrameNode));
        tmp->frame = addFrame(fr);
        while (help->next != NULL)
        {
            help = help->next;
        }
        help->next = tmp;
    }
    else
    {
        list = (FrameNode*)malloc(sizeof(FrameNode));
        FrameNode* tmp = (FrameNode*)malloc(sizeof(FrameNode));
        tmp->frame = addFrame(fr);
        list = tmp;
    }
}

I really need help, I have to submit it by Sunday. If you notice any more problems please tell me Thank you to everyone!!!!!

Answer 1

A separate struct for a linked list usually adds nothing but complexity. Why not just use:

struct my_frame {
    struct my_frame *next;
    char *name;
    int duration;
    char *path;
}

It reduces complexity and simplifies memory allocation.

A few personal preferences: I suggest using a prefix to prevent generic names like "frame". I also suggest dropping the typedef. It does nothing for you. It only adds obscurity. Drop the capitals in type names. If you want to program in C, learn C don't try to make it look like C++, C# or Java.

Answer 2

At the end of the addFrame function you free p , but then you return it.

So in the line tmp->frame = addFrame(fr); in the function insertAtEnd , you assign a pointer that has been freed already, whose contents are unknown.

The solution is to simply remove the line free(p) in addFrame , but make sure that you have a free'ing mechanism later in your program for this list.

Edit: also, I now see that in the line list = tmp;, you are actually assigning a value to the local variable list , and what you should be doing is *list = tmp .