Below is our list example code.

list.h

#ifndef __LIST_H__
#define __LIST_H__

typedef struct {
    unsigned length;
    int *array;
} List;

// Construct, destruct
List *makeList();
void destroyList(List *);

// Add to end of list
void append(List *list, int val);
#endif 

list.c

#include <stdlib.h>
#include "list.h"

List *makeList() {
    // Space for a List struct
    List *ans = (List *) malloc(sizeof(List));

    // Initially an empty list
    ans->length = 0;
    ans->array = (int *) malloc(ans->length * sizeof(int));

    return ans;
}

void destroyList(List *list) {
    // Avoid use after free! Free array first.
    free(list->array);
    free(list);
}

// Example code (not shown in lecture):
void append(List *list, int val) {
    // Increase the size of the list by 1
    list->length += 1;

    // Reallocate the memory for our array to include more space.
    // realloc() will copy over the original bytes, but no guarantees
    // on the other bytes after that.
    list->array = (int *) realloc(list->array, list->length * sizeof(int));

    // Store the new value at the end of the array.
    list->array[list->length - 1] = val;
}

useList.c

This is some example code that uses the list above. Note that we #include "list.h" so that the typechecker knows what our list looks like and what the functions are. We will then compile this by compiling both C files together: clang list.c useList.c.

#include <stdio.h>
#include "list.h"

int main() {
    List *myList = makeList();

    printf("%p\n", myList);

    // Append some values
    append(myList, 42);
    append(myList, 175);
    
    // Print out the list
    for (int i = 0; i < myList->length; i+=1) {
        printf("%d\n", myList->array[i]);
    }

    puts(""); // To get a new line

    return 0;
}