/*
 * This trivial program illustrates how to open files.  We present the
 * following use cases:
 *
 * - create a non-existent file
 * - "create" an existing file
 * - fail to create an existing file
 * - open an existing file
 * - fail to open a non-existing file
 * - truncate an existing file
 */

#include <sys/stat.h>

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

void
createFile() {
	int fd;

	if ((fd = open("./newfile", O_RDONLY | O_CREAT,
					S_IRUSR | S_IWUSR)) == -1) {
		fprintf(stderr, "Unable to create './newfile': %s\n",
				strerror(errno));
		exit(EXIT_FAILURE);
	}

	printf("'./newfile' created. File descriptor is: %d\n", fd);

	/* We are leaking a file descriptor here to illustrate that they
	 * are increasing as we open more files.  Normally, we would call
	 * close(2) whenever we're done using the decriptor. */
}

void
failExclFileCreation() {
	int fd;

	if ((fd = open("./newfile", O_RDONLY | O_CREAT | O_EXCL,
					S_IRUSR | S_IWUSR)) == -1) {
		fprintf(stderr, "Unable to create './newfile': %s\n",
				strerror(errno));
	}

	/* We expect this to fail! */
	if (close(fd) == -1) {
		fprintf(stderr, "Closing failed: %s\n", strerror(errno));
	}
}


void
failOpenNonexistingFile() {
	int fd;

	if ((fd = open("./nosuchfile", O_RDONLY)) == -1) {
		fprintf(stderr, "Unable to open './nosuchfile': %s\n",
				strerror(errno));
	}

	/* This will fail.  So be it. */
	(void)close(fd);
}

void
openFile() {
	int fd;

	if ((fd = open("./openex.c", O_RDONLY)) == -1) {
		fprintf(stderr, "Unable to open './openex.c': %s\n",
				strerror(errno));
		exit(EXIT_FAILURE);
	}

	printf("'./openex.c' opened. File descriptor is: %d\n", fd);

	(void)close(fd);
	printf("'./openex.c' closed again\n");
}

void
truncateFile() {
	int fd;

	if ((fd = open("./newfile", O_RDONLY | O_TRUNC)) == -1) {
		fprintf(stderr, "Unable to open './newfile': %s\n",
				strerror(errno));
		exit(EXIT_FAILURE);
	}

	printf("'./newfile' opened. File descriptor is: %d\n", fd);
	printf("'./newfile' truncated -- see 'ls -l openex'\n");

	(void)close(fd);
}



int
main(int argc, char **argv) {
	createFile();
	system("ls -l newfile");
	printf("\n");
	sleep(2);

	createFile();
	system("ls -l newfile");
	printf("\n");
	sleep(2);

	failExclFileCreation();
	printf("\n");
	sleep(2);

	openFile();
	printf("\n");
	sleep(2);

	failOpenNonexistingFile();
	printf("\n");
	sleep(2);

	printf("cp openex.c newfile\n");
	system("cp openex.c newfile");
	system("ls -l newfile");
	truncateFile();
	system("ls -l newfile");

	return 0;
}