function declaration is described by interface but I can't assign names-CodePudding

I have been given a function interface that looks like this:

typedef enum order (*cmp_fun)(const void *x, const void *y);
bool tree_member(cmp_fun, const void *, const struct tree *);
const struct tree *tree_insert(cmp_fun, const void *, const struct tree *);

When I try to give the function pointer a name and implement the function I get a compiler error and I'm not sure what I'm doing wrong:

bool tree_member(order (*funcptr), const void* test_value, const struct tree* my_tree){... ///?

const struct tree* tree_insert(int (*funcptr), const void* insert_value, const struct tree* my_tree){... //???

There is something about the function declaration for accepting the function pointer as a parameter that I am not understanding

 In file included from tree-examples.c:21:
tree.c:15:18: error: unknown type name ‘order’
   15 | bool tree_member(order (*funcptr), const void* test_value, const struct tree* my_tree){
      |                  ^~~~~
tree.c:22:20: error: conflicting types for ‘tree_insert’
   22 | const struct tree* tree_insert(int (*funcptr), const void* insert_value, const struct tree* my_tree){
      |                    ^~~~~~~~~~~

I have tried many many variations:

bool tree_member(cmp_fun (*funcptr), const void* test_value, const struct tree* my_tree){


const struct tree* tree_insert(cmp_fun (*funcptr), const void* insert_value, const struct tree* my_tree){

CodePudding user response：

The compiler is telling you that it doesn't recognize order as a type name. You need to write enum order instead of just order.

Looking at that part of the code, I noticed you used the wrong type for the first argument of the tree_member function. The interface is telling you that the first argument of tree_member must have type cmp_fun, but you accidentally made it have type order *.

The compiler is also telling you that the tree_insert implementation you wrote has the wrong type. Look carefully at the first argument of tree_insert. It is supposed to be a cmp_fun according to the interface, but you accidentally made your first argumet be an int * instead.

Hint: Instead of typing your function implementations in from scratch, you can simply copy the declaration you were given, replace ; with { }, and add a name for any arguments that are missing a name. Following this hint, you would get this code as a starting point:

bool tree_member(cmp_fun cmp, const void * ptr,
  const struct tree * my_tree)
{
}

const struct tree * tree_insert(cmp_fun cmp, const void * ptr,
  const struct tree * my_tree)
{
}