Initialization discards qualifiers from pointer target type

c linked-list
Crystal picture Crystal · Feb 23, 2010 · Viewed 84.1k times · Source

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

GManNickG picture GManNickG · Feb 23, 2010

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."

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