Adding an item to a single-linked list. Incomprehensible operations

Question

First create a structure

struct LIST { int field; struct LIST *pNext; }; struct LIST* pHead; инициализирую первый элемент struct LIST* init(int number) { struct LIST *lst; lst = (struct LIST*)malloc(sizeof(struct LIST)); lst->field = number; lst->pNext = NULL; return lst; }; struct LIST* add(struct LIST* lst, int number) { struct LIST * pNew; pNew = (struct LIST*)malloc(sizeof(struct LIST)); pNew->field = number; pNew->pNext = lst->pNext; //2 lst->pNext = pNew; //3 return pNew; } int main() { pHead = init(5); struct LIST* pTmp = add(pHead, 10); }

Question: how does the add function work, it is especially incomprehensible what is being done here, what happens with pointers and how to understand this lst-> pNext Why does the call have to happen via pNew and how does it differ from the call with lst?

 pNew->pNext = lst->pNext; //2 lst->pNext = pNew; //3

And can you please explain what the program does in general?

Accepted Answer · 2018-04-12T18:12:32

This is not an add, but an insert after the lst element. The function should be called insert .

The lst object has a pointer to the list item that follows it. The function inserts a new pNew element after lst . therefore

 lst->pNext = pNew;

but the element that used to follow lst will now go after pNew . therefore

 pNew->pNext = lst->pNext;

These two actions are performed in the reverse order in order not to overwrite the initial value lst->pNext .

treatment ... via pNew and how it differs from treatment using lst

These are pointers to two different objects. It's not entirely clear what you want to ask.

and what lst-> pNext generally does, how does this composite type pointer interact with pNext? Does each pNew or lst have its own pNext?
Can you imagine the meaning of the words "simply linked list"?
c work, but apparently it’s a chain, “carriages” of the same type, interconnected by pointers, and it seems to be all recursive

Adding an item to a single-linked list. Incomprehensible operations

1 answer 1

More articles: