Having issues implementing a linked list ADT with a function pointer.

**max force** · 01-16-2017

So I have been working on this without much cause for celebration.

I have implemented the creation of the list, the push and pop aspects of it and the iterator for which you traverse the list. However there is one aspect that aludes me which is this function pointer that I am having trouble "baking into" my list.

The function pointer in question is:

typedef int (*cmpfunc_t)(void *, void *); specifically I have never encountered one of these before and googling it yielded little to no answers for how to proceed.

My code in its entirety: common.h * GitHub

Any help would be appreciated!

**algorism** · 01-16-2017

I can't compile your program:
* common.h is missing some lines from the top
* list.c is missing at least one line from the bottom.
* list.h is missing entirely.
* there's no main.

You should also maximize your compiler's warning level to help catch unused variables and the like. For example, in list_popfirst, you set tmp but never use it.

In list_create, the given comparison function is supposed to be stored in the list structure. list_contains and list_sort are supposed to use this sort function.

It is strange and presumably wrong that you are creating a new node in list_contains and then comparing addresses. You need to compare the "elements" using the comparison function. BTW, "elements" is a weird name for what is essentially the "data" of the node.

**Salem** · 01-17-2017

Declaring compatible functions, and calling them via function pointers.

Code:

#include<stdio.h>

typedef int (*cmpfunc_t)(void *, void *); 

int foo ( void *a, void *b ) {
  int *pa = a;
  int *pb = b;
  return *pa - *pb;
}

int main()
{
  int a = 7, b = 4;
  cmpfunc_t fn = foo;
  int result = fn(&a,&b);
  printf("a=%d, b=%d, result=%d\n", a, b, result);
  return 0;
}

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