Dynamically allocate and add a structure inside a linked chain

Question

I am facing a problem concerning the dynamic allocation of structure, a linked chain containing a pointer to a structure to be more specific.

Code of the linked chain:

typedef struct Queue Queue;
struct Queue{
    Real* elmt;
    Queue* next;
    Queue* prev;
};

So, this struct is circular, with next pointing to the next

Code of struct Real(which represents):

typedef struct Real Real;
struct Real{
    int* nb; //int array containing the number
    size_t size;
    int neg; /*0=positive 1=negative*/
    int com; /*-1 = no comma, otherwise integer indicating the position*/
};

So, as explained, I wish to dynamically allocate a queue containing several elements, so I created this function:

Queue* mallocQueueElmt(const Real* arg){
    Queue* res=NULL;

    res=mallocQueue();

    res->elmt=NULL;
    res->elmt=mallocReal(arg->size);

    memmove(res->elmt->nb, arg->nb, sizeof(int)*arg->size);

    res->elmt->com=arg->com;
    res->elmt->neg=arg->neg;

    res->next=res;
    res->prev=res;

    return res;
}

mallocReal() just returns a pointer pointing at a Real structure containing a pointer(meaning the member nb of the structure Real) pointing at an array(dynamically allocated) of int with a size equal to arg->size

This works, I tested it with a function :

void printQueue(Queue* arg){
    Queue* cur=NULL;
    cur=arg->prev;

    if(cur == arg->prev){;
        printReal(cur->elmt);
        printf(" ");
    }
    else    
        while(cur != arg){
            cur=cur->next;
            if(cur->elmt){
                printReal(cur->elmt);
                printf(" ");
            }else{
                printf("no element ");
            }
        }


}

But when I try to add an element, thanks to this function:

Queue* addElement(Queue* arg, const Real* arg1){
    Queue* res=NULL;

    res=mallocQueue();

    res->elmt=NULL;
    res->elmt=mallocReal(arg1->size);

    memmove(res->elmt->nb, arg1->nb, sizeof(int)*arg1->size);

    res->elmt->neg=arg1->neg;
    res->elmt->com=arg1->com;

    res->prev=arg->prev;
    res->next=arg;
    res->prev->next=res;
    arg->prev=res;

    res=arg;

    return res; 
}

and recall printQueue(), then only the second element(so added with addElement()) is displayed, and nothing anormal happened, everything seemed to be running fine.

Thank you in advance for your help

Answer 1

Your if statement in printQueue will always only print the lastly added item in the queue.

Try something like this instead:

void printQueue(Queue* arg){
    Queue* cur=arg;

    do {
        printReal(cur->elmt);
        printf(" ");

        cur=cur->next;
    } while (cur != arg);
}