1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 | #include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>
/* TIPS and BEST PRACTICES for linked lists
* ∙ Avoid duplication.
* - Avoid needless special cases.
* ∙ Draw box-arrow diagrams.
* - Write the step number on the diagram.
* ∙ Be careful about order.
* - To check yourself, try drawing box-arrow diagram if you flipped two key lines.
* ∙ Read error message. Ask for explanation of message if needed.
*
* You are encouraged to post error messages on Piazza.
*/
typedef struct _Node {
//int value;
void* a_value;
struct _Node* next;
} Node;
void print_list(Node* head, void(*print_one_element_fn)(void*)) {
// print_one_element_fn(…) is a function
for(Node* curr = head; curr != NULL; curr = curr -> next) {
printf("[");
print_one_element_fn(curr -> a_value); // print this element
printf("]");
if(curr -> next != NULL) { // If curr is not the tail...
printf("→");
}
}
printf("\n");
}
//void _append(int value, Node** a_head, Node** a_tail) {
void _append(void* a_value, Node** a_head, Node** a_tail) {
// Do not copy this code (or any other code). Default is always no copying.
// Allocate memory on heap for a new node.
Node* new_node = malloc(sizeof(*new_node));
// Initialize fields of the new node using a COMPOUND LITERAL.
*new_node = (Node) { .a_value = a_value, .next = NULL };
if(*a_head == NULL) { // If list is empty (size=0), initialize a list of size one.
assert(*a_tail == NULL);
*a_head = new_node;
}
else {
assert(*a_head != NULL && *a_tail != NULL); // List not empty «before» appending new node
(*a_tail) -> next = new_node; // Connect tail to new node.
} // ⚠ Do not switch the order of these two steps!!!
*a_tail = new_node; // Set tail to new node.
assert(*a_head != NULL && *a_tail != NULL); // List not «after» before appending new node
assert((*a_tail) -> a_value == a_value);
assert((*a_tail) -> next == NULL); // Tail's '.next' field must always be NULL.
}
void free_list(Node** a_head, Node** a_tail) {
// Convenience variables
Node* head = *a_head;
Node* tail = *a_tail;
while(head != NULL) { // While the list is not empty
Node* old_head = head; // Don't lose your head.
head = head -> next; // Second node becomes the new of the list.
free(old_head); // Free your mind.
}
// HW12: Free any heap memory that the node refers.
// Set the head and tail in the caller's stack frame to NULL.
*a_head = NULL;
*a_tail = NULL;
}
void _print_int(void* a_n) {
int n = *((int*)a_n);
printf("%d", n);
}
int main(int argc, char* argv[]) {
Node* head = NULL;
Node* tail = head;
int n1 = 5, n2 = 6, n3 = 7;
_append(&n1, &head, &tail);
_append(&n2, &head, &tail);
_append(&n3, &head, &tail);
print_list(head, _print_int);
free_list(&head, &tail);
assert(head == NULL && tail == NULL); // List should be empty now.
return EXIT_SUCCESS;
}
/* vim: set tabstop=4 shiftwidth=4 fileencoding=utf-8 noexpandtab: */
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