Thread: passing (...) as parameter

look for va_arg sample

Hello,

I've looked into the function passed, absolutely interesting. However I realized I don't know how I could you use it in my intended purpose, i.e declaration and definition of a linked list of integers.

The 'dirty' way is:

Code:

struct le{
	int key;
	struct le* next;
	struct le* prev;
} ; typedef struct le LE;

in main: 
LE* list = (LE*) malloc(sizeof(LE));
	list->key = 2;
	list->next = (LE*) malloc(sizeof(LE));
	list->next->key = 14;
	list->next->next = (LE*) malloc(sizeof(LE));
	list->next->next->key = 56;
	list->next->next->next = (LE*) malloc(sizeof(LE));
	list->next->next->next->key = 98;
	list->next->next->next->next = (LE*) malloc(sizeof(LE));
	list->next->next->next->next->key = 4;
	list->next->next->next->next->next = (LE*) malloc(sizeof(LE));
	list->next->next->next->next->next->key = 34;
	list->next->next->next->next->next->next = (LE*) malloc(sizeof(LE));
	list->next->next->next->next->next->next->key = 18;
	list->next->next->next->next->next->next->next = (LE*) malloc(sizeof(LE));
	list->next->next->next->next->next->next->next->key = 1;
	list->next->next->next->next->next->next->next->next = (LE*) malloc(sizeof(LE));
	list->next->next->next->next->next->next->next->next->key = 0;
	list->next->next->next->next->next->next->next->next->next = (LE*) malloc(sizeof(LE));
	list->next->next->next->next->next->next->next->next->next->key = 88;

But any loop/recursive solution? Besides above I didn't allocates and point the prev pointers, which would double the lines of code.

start by providing some API for working with your list

like

list_inseart(LE** pList, int newValue);
list_print(LE* List);

etc

when you'll have such functions for working with the list - writing a function that adds arbitrary number of integers will be a lot easier

Originally Posted by simpatico_qa

But if so, initializing the listnode shall always be the long way I did? I've functions that work on the list but they don't declare and define nodes.

why?

Originally Posted by simpatico_qa

because I asked for code that given a size and/or values will declare and define a list node accordingly. Yet u replied with something else (creating elements one at the time, when needed).

vart is just suggesting good code architecture. It doesn't bear directly on variable arguments but it's still good advice.

I would suggest a function skeleton like this:

Code:

#include <stdarg.h>

LE* listConstructor(int n2, ...)
{
    LE *list = NULL;
    va_list valist;

    va_start(valist, n2);
    while(n2 > 0)
    {
        list = listAppend(list, va_arg(valist, LE *));
        --n2;
    }
    va_end(valist);
    return list;
}

This assumes a listAppend() function which appends the given element to the list... In practice this function will be a bit more complicated, but it shows how to use the va_* functions

Originally Posted by simpatico_qa

Code:

void setPrevLinks(LE* lis){
	if (lis != NULL) return;

So, you return if the pointer is NOT null? And you continue if it is? Hmm...