Crystal Crystal - 1 month ago 26
C Question

Initialization discards qualifiers from pointer target type

I'm trying to print the list of a singly linked list that I referred to in link text. It works, but I do get the compiler warnings:


Initialization discards qualifiers from pointer target type



(on declaration of start = head) and


return discards qualifiers from pointer target type



(on return statement) in this code:

/* Prints singly linked list and returns head pointer */
LIST *PrintList(const LIST *head)
{
LIST *start = head;

for (; start != NULL; start = start->next)
printf("%15s %d ea\n", head->str, head->count);

return head;
}


I am using XCode. Any thoughts?

Answer

It's this part:

LIST *start = head;

The parameter for the function is a pointer to a constant, const LIST *head; this means you cannot change what it is pointing to. However, the pointer above is to non-const; you could dereference it and change it.

It needs to be const as well:

const LIST *start = head;

The same applies to your return type.


All the compiler is saying is: "Hey, you said to the caller 'I won't change anything', but you're opening up opportunities for that."