Question

Is there a way to write a single function ( addnode ) for different structures? I’ve this scenario:

typedef struct linkedlist_a *ptr_a;
typedef struct linkedlist_a
{
    /* content */
    ptr_a next;
} listA;

typedef struct linkedlist_b *ptr_b;
typedef struct linkedlist_b
{
    /* content */
    ptr_b next;
} listB;

listA *listA_addnode( listA *head, listA *node )
{
    listA *temp = head;
    if( temp == NULL )
    {
        temp = node;
    }
    else if( temp -> next == NULL )
    {
        temp -> next = node;
    }
    else
    {
        while( temp -> next ) temp = temp -> next;
        temp -> next = node;        
    }

    return head;
}


listB *listB_addnode( listB *head, listB *node )
{
    listB *temp = head;
    if( temp == NULL )
    {
        temp = node;
    }
    else if( temp -> next == NULL )
    {
        temp -> next = node;
    }
    else
    {
        while( temp -> next ) temp = temp -> next;
        temp -> next = node;        
    }

    return head;
}

If there’s two structuress is ok for me write two function but in case I’ve more than 2, how can I do?

Answer 1

Instead of having different structs that represent a linked list a possible solution would be to have single linked list struct that has void* member for data. This would allow a single add_node() function with a slightly different signature.

For example:

struct linked_node
{
    void* data;
    struct linked_node* next;
};

void add_node(struct linked_node** a_head, void* a_data)
{
    struct linked_node* new_node = malloc(sizeof(*new_node));
    new_node->data = a_data;
    new_node->next = 0;
    if (!*a_head)
    {
        *a_head = new_node;
    }
    else
    {
        /* ... */
    }
}

There is a danger with this approach, namely the correct interpretation the data member. However, with care this approach would meet your requirements.

Example use (error checking omitted):

struct data_x { int i; char c; };
struct data_y { char* s; };

struct linked_node* list_x = 0;
struct data_x* dx = malloc(sizeof(*dx));
dx->i = 4;
dx->c = 'a';

add_node(&list_x, dx);

if (list_x)
{
    struct data_x* x = list_x->data;
    printf("x.i=%d x.c=%c\n", x->i, x->c);
}

struct linked_node* list_y = 0;
struct data_y* dy = malloc(sizeof(*dy));
dy->s = "hello";

add_node(&list_y, dy);

if (list_y)
{
    struct data_y* y = list_y->data;
    printf("y.s=%s\n", y->s);
}

See online demo http://ideone.com/iZO8h.