My du implementation

du.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <sys/stat.h>

off_t* count_filesize_of_directory(char *path) {
	DIR *dir = opendir(path);
	if (dir == NULL) {
		perror("error while reading directory");
		return NULL;
	}
	struct dirent *dir_entry;

	off_t *size = malloc(sizeof(off_t));
	if (size == NULL) {
		perror("out of memory");
		return NULL;
	}

	while ((dir_entry = readdir(dir)) != NULL) {
		if (strcmp(dir_entry->d_name, ".") == 0 || strcmp(dir_entry->d_name, "..") == 0) {
			continue;
		}
		size_t complete_path_length = strlen(path) + strlen(dir_entry->d_name) + 2;
		char* complete_path = malloc(sizeof(char) * complete_path_length);
		if (complete_path == NULL) {
			perror("out of memory");
			return NULL;
		}
		snprintf(complete_path, complete_path_length, "%s/%s", path, dir_entry->d_name);

		if (dir_entry->d_type != DT_DIR) {
			struct stat stat_buf;
			if (stat(complete_path, &stat_buf) != 0) {
				perror("error while getting stat from file");
				return NULL;
			}
			*size += stat_buf.st_size;
		} else if (dir_entry->d_type == DT_DIR) {
			off_t *d_size = count_filesize_of_directory(complete_path);
			if (d_size == NULL) {
				return NULL;
			}
			printf("%lld\t%s\n", *d_size, complete_path);
			*size += *d_size;
			free(d_size);
		}
		free(complete_path);
	}
	closedir(dir);
	return size;
}

int main(int argc, char* argv[]) {
	char* directory = ".";
	if (argc > 1) {
		directory = argv[1];
	}

	off_t* filesize = count_filesize_of_directory(directory);
	if (filesize == NULL) {
		return 1;
	}

	printf("%lld\n", *filesize);

	free(filesize);
	return 0;
}