Help for my code

Hello everyone,
I'm new entry here, my name is Jacopo, from Italy.
I'm trying study c language and I have write a code to make a list but now I need some help for this.
So, this is not exactly my code, this is only a test code that I did to check memory address of list elements

Code:

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#include <stdio.h>


struct Element {
    int info;
    struct Element *next;
    struct Element *prev;
};


struct Element New_Element(int info);


int main(int argc, char **argv)
{
    int a, c;
    printf("How many elements do you want put in? ");
    scanf("%d", &c);
    for (int h = 0; h < c; h++) {
        printf("Insert a: ");
        scanf("%d", &a);
        struct Element e = New_Element(a);
        printf("Elemento%d struct address: %p \n\n", h, &e);
    }
    return 0;
}

struct Element New_Element(int info) {
    struct Element e = {info, NULL, NULL};
    return e;
}

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My issue is that the compiler assign every time the same memory location to each elements (see image below). This isn't good to me because I need to have a pointers that point different elements and therefore different memory address.
How can I do this?
Ps. My english is not perfect, sorry :(

Attachment 15349

You need to call malloc if you want a dynamic number of elements to exist in your program.

Thanks for reply me.
I'm able to use malloc function to make dynamic array, but how can I use malloc to initialize struct?

Quote:

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Originally Posted by Jacopo

I'm able to use malloc function to make dynamic array, but how can I use malloc to initialize struct?

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You can't, but then once you have your dynamic array of struct objects thanks to malloc, you can loop over the array and assign initial values to the members of each struct object.

mh, can you show me an example?

Quote:

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but then once you have your dynamic array of struct objects thanks to malloc

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How? :confused:

Ok, I have tried to rewrite my code with the malloc function but the result not change..Where am I doing wrong?

Code:

---

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


struct Element {
    int info;
    struct Element *next;
    struct Element *prev;
};


struct Element *New_Element(int info);


int main(int argc, char **argv)
{
    int a, c;
    printf("How many elements do you want put in? ");
    scanf("%d", &c);
    for (int h = 0; h < c; h++) {
        printf("Insert a: ");
        scanf("%d", &a);
        struct Element e = *New_Element(a);
        printf("Elemento%d struct address: %p \n\n", h, &e);
    }
        return 0;
}


struct Element *New_Element(int info) {
    struct Element *e = malloc(sizeof(struct Element));
    (*e).info = info;
    (*e).next = NULL;
    (*e).prev = NULL;
    return e;
}

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You should print e, not &e.

struct Element *e = New_Element(a);
printf("Elemento%d struct address: %p \n\n", h, e

Quote:

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Originally Posted by Salem

You should print e, not &e.

struct Element *e = New_Element(a);
printf("Elemento%d struct address: %p \n\n", h, e

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Yeah I was writing this right now! :D
Thanks to all!

So, this code works but my last doubt...is this the best way to initialize an struct (or this type of struct)?

Code:

---

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


struct Element {
    int info;
    struct Element *next;
    struct Element *prev;
};


struct Element *New_Element(int info);


int main(int argc, char **argv)
{
    int a, c;
    printf("How many elements do you want put in? ");
    scanf("%d", &c);
    for (int h = 0; h < c; h++) {
        printf("Insert a: ");
        scanf("%d", &a);
        struct Element *e = New_Element(a);
        printf("Elemento%d struct address: %p \n\n", h, e);
    }
    return 0;
}


struct Element *New_Element(int info) {
    struct Element *e = malloc(sizeof(struct Element));
    (*e).info = info;
    (*e).next = NULL;
    (*e).prev = NULL;
    return e;
}

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Looks good, but a few things you can do to clean it up:

• malloc can return NULL if it fails (see man page), so you should check for that. If you don't and it returns NULL, you will end up trying to access memory you don't own, which causes undefined behavior.
• I generally use the variable itself (dereferenced) in the sizeof. That's one less thing to change if for any reason you rename the struct Element to something else.
• I prefer the -> notation to (*). for struct member access; it seems cleaner.

Taking those into account, your function might look something like:

Code:

---

struct Element *New_Element(int info) {
    struct Element *e = malloc(sizeof(*e));
    if (e != NULL) {
        e->info = info;
        e->next = NULL;
        e->prev = NULL;
    }
    return e;
}

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