Question

In the header file I have the following line:

typedef int comparator(int* left, int* right);

But when I tried to write a function definition for it like so:

int comparator (int* left, int* right){
    if(left<right) {
        return 1;
    } else if(right>left) {
        return -1;
    } else {
        return 0;
    }   
}

The error I get is:

file.c:10: error: ‘comparator’ redeclared as different kind of symbol

The function must be typedef’ed because later on in the header file it is used in a method prototype like so:

struct bst_node** search(struct bst_node** root, comparator compare, void* data);

So how is this method constructed?

Answer 1

in your header file you should just have

 int comparator(int* left, int* right);

your aren’t declaring a type, but just declaring a function.

you could declare a function pointer type called comparator…

typedef int (*comparator)(int* left, int* right);

but you wouldn’t then make a function called comparator. you just need to make a function with the same signature

int ascending_comparator(int* left, int* right)
{
    // comparison
} 

then call

search(root, ascending_comparator, data);

Also, I got a feeling you don’t want to be passing int* but actual int, or in your function you don’t want to be comparing the pointers, but comparing the values of what each int is pointing to, like

int comparator (int* left, int* right){
    if(*left < *right) {
        return 1;
    } else if(*right > *left) {
        return -1;
    } else {
        return 0;
    }   
}

but possibly you are wanting to compare the memory locations where the ints are stored.

also your comparisons are the same

if(left < right) 

is the same as

if( right > left)

so maybe you want

 int comparator (int* left, int* right){
        if(*left < *right) {
            return 1;
        } else if(*left > *right) {
            return -1;
        } else {
            return 0;
        }   
    }