freshmre / c-heap

Simple min-max heap/priority queue library written in C which can store any type

C Heap Library

A simple heap data-structure library for C. It can store any type provided that the used supplies the size of the elements. Elements may be added of removed using library calls.

To start:

1. #include heap.h
2. Define cmp_f that compares priorities between any two elements
3. Initialize a max-heap: heap *h = init_heap(cmp_f, Max_Heap, 1024);

h now may hold 1024 values before the need to be resized automatically.

cmp_f is required to:

• Have the signature int cmp_f(void *a, void *b)
• Return a positive integer if a ranks higher than b
• Return a negative integer if a ranks lower than b
• Return zero if a and b rank equally

To add an element:

// Push an int v
push_heap(h, &v, sizeof(int));

// Push a char c
push_heap(h, &c, sizeof(char));

// Push a string pointed to by s
push_heap(h, s, strlen(s) + 1); // Note that you need to add one to include the nul terminator

To get the element at the top (of the highest priority):

int *top = pop_heap(h) // Removes the element from the heap restructuring the heap

int *peek_top = peek_heap(h); // Doesn't modify the heap

Note that it is the responsibity of the user to free top, as it has been seperated from the heap and won't be free'd upon the call to free_heap which only takes care of what's left in the heap.

Reference sheet

Action	Code	Notes
Initialize min- or max-heap	heap *h = init_heap(cmp_f, Min_Heap, 1024);	use Min_Heap or Max_Heap as type for respective heap type
Check whether heap is empty	int empty = is_empty(h);	returns 1 if empty, 0 otherwise
Push float f into heap	push_heap(h, &f, sizeof(f));
Get pointer to float on top of the heap without removing it	float *top_fl = peek_heap(h);
Get pointer to float on top of the heap and removing it	float *popped_fl = pop_heap(h);	freeing popped_fl is up to you
Free heap and all elements it currently contains	heap_free(h)