OS - Optimal Page Replacement

main.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define CHUNK_SIZE 10


char *read_pages(size_t *len) {
	size_t page_len = 0, pages_size = CHUNK_SIZE;
	char *pages = (char *) calloc(pages_size + 1, sizeof(char));

	FILE *page_file = fopen("page.txt", "r");
	while (fscanf(page_file, "%c ", pages + page_len) != EOF) {
		if (++page_len >= pages_size) {
			pages_size += CHUNK_SIZE;
			pages = realloc(pages, pages_size + 1);
			if (pages == NULL) {
				perror("realloc error");
				exit(-1);
			}
		}
	}
	fclose(page_file);
	pages[page_len] = 0;
	*len = page_len;
	return pages;
}

void print_frame(char *frames, int len) {
	for (int i = 0; i < len; ++i)
		printf("%c ", frames[i]);
	printf("\n");
}

void optimal(char *full_pages, char *frames, int frames_len) {
	int page_faults = 0;

	for (int i = 0; i < strlen(full_pages); ++i) {
		if (strchr(frames, full_pages[i]) == NULL) {
			++page_faults;

			char *empty_frame = strchr(frames, 0);
			if (empty_frame < frames + frames_len) {
				*empty_frame = full_pages[i];
			} else {
				int victim, max = -1, tmp;
				char *page_addr;
				for (int j = 0; j < frames_len; ++j) {
					page_addr = strchr(full_pages + i, frames[j]);
					if (page_addr == NULL) {
						victim = j;
						break;
					}
					if ((tmp = page_addr -  full_pages + i) > max) {
						max = tmp;
						victim = j;
					}
				}
				frames[victim] = full_pages[i];
			}
		}
		print_frame(frames, frames_len);
	}
	printf("\nPage Faults = %d\n", page_faults);
}

int main(void) {
	int frames_len;
	printf("Length of frames: ");
	scanf("%d", &frames_len);
	char *frames = (char *) calloc(frames_len + 1, sizeof(char));

	size_t page_len;
	char *pages = read_pages(&page_len);
	
	printf("Reference strings:");
	for (int i = 0; i < page_len; ++i) {
		printf(" %c", pages[i]);
	}
	printf("\n\n");

	optimal(pages, frames, frames_len);

	return 0;
}

page.txt

7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1