#include <stdio.h>  /* for error messages */
#include <stdlib.h> /* for exit() */

#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>


/*  Sample code for creating a file with holes.
 *  Author:  Mark A. Sheldon, (c) 15 March 2007
 * 
 *  Usage:  seeky filename string1 len1 offset string2 len2
 *  opens filename for writing.  The file must NOT exist, and will be
 *  created.
 *  len1 bytes are written starting with string1 at the start of the
 *  file. 
 *  Then seeks to position offset in file and writes len2 bytes
 *  starting with string2.
 */
char *usage_fmt = "Usage:  %s filename string1 len1 offset string2 len2\n";

int main (int argc, char **argv)
{
	int fd, rtn;
	int len1 = 0, offset = 0, len2 = 0;
	char *prog_name = argv[0], *string1, *string2;

	if ((argc != 4) && ((sscanf(argv[3], "%d", &len1) != 1)
			    || (sscanf(argv[4], "%d", &offset) != 1)
			    || (sscanf(argv[6], "%d", &len2) != 1))) {
		fprintf(stderr, usage_fmt, prog_name);
		exit(EINVAL);
	}
	string1 = argv[2];
	string2 = argv[5];

	fd = open(argv[1], (O_WRONLY | O_CREAT | O_EXCL), (S_IRUSR | S_IWUSR));
	if (fd == -1) {
		perror("Cannot open file");
		exit(errno);
	}

	/* Note:  not checking for short writes.  For lab it's ok. */
	if ((rtn = write(fd, string1, len1)) == -1) {
		perror("Cannot write file");
		exit(errno);
	}
	if ((rtn = lseek(fd, offset, SEEK_CUR)) == (off_t) -1) {
		perror("Cannot seek");
		exit(errno);
	}
	/* Note:  not checking for short writes.  For lab it's ok. */
	if ((rtn = write(fd, string2, len2)) == -1) {
		perror("Cannot write file");
		exit(errno);
	}

	if ((rtn = close(fd) == -1)) {  
		perror("Cannot close file");
		exit(errno);
	}
	return 0;
}